Switch mode supply mod

[Hyena]

So you've been charging packs happily with it buzzing like that ? Or did you turn it off when you heard it ?
My packs were around 3.8-3.9v/cell when I tested and heard it too. Maybe it's to do with the voltage difference between the supply output and the battery that's causing it ?
Actually, now that I think of if I've got one of those universal laptop chargers that I was playing around with initially as lipo chargers and when I increased the voltage to more than the the pack rating (eg if I had a pack at 14v that should have charged to 16.8v but I set the voltage to 18v temporarily) it'd make that arcing/buzzing noise then shut down. Luckily power cycling fixed it, but maybe its the same deal in our meanwells ?

[mwkeefer]

Hyena,

I charge right through the buzzing..

I must admit turning it down a bit (current) so it stays under 350 seems to cut the noise in half but again - I did a top off on a pack which I haven't tested using the meanwell yet and it was silent!

I suspect as we shift the voltage regulation circuitry upwards... we also change the duty cycle which is already way too high but more importantly I believe we are changing the operating frequency (drift and shift baby)... Fechter can scope this if he has time to see what's happening (or I can take it to my local electronics repair guy... who has recently developed a new respect for me, he loves this homebrew kit stuff!).

If it turns out to be as I suspect.... we are changing the Ct/Rt network timing through the voltage bump... we just need to recalculate the proper Ct/Rt for proper oscillator speed... the current limiting will handle PWM and DTC for us (Pulse width modulation and Dead time control) which will handle the total power output and curve point.

The next pack I charged was the BUZZER pack... When I was charging 5S3P using these at 20.7v they buzzed then too but hadn't been adjusted for proper current output of 350w.

Im going to split this buzzing pack apart after the next discharge cycle (5AM coffee run to wawa) but I should add that I blew a bit off the non-buzzer pack earlier (just a miles ride) and didn't get a bit of buzz out of that pack when I topped it off + I felt more performance out of it (I swear it was performance not the cold).

Who knows? I'll continue testing... I have even gone as far as running a 40' 20A extension cord from a dedicated breaker with nothing else attached to the mains just in case my 6+ pcs and other equipment in my home lab were causing feedback. The fan was causing some noise for sure when in the same breaker bar... I think the CFLs may have played a part also.

Do you have the cases grounded to earth? I never bothered (never do) but that could also be part of the issue I suppose... but yes I've done > 10 charges while monitoring current and temperatures (pack and charger) and so I just left it buzz... the source seems to be the largest yellow covered "transformer" or whatever it is, closest to the front of the supply.

I keep hearing my ion generator going buzzz... thinking I left the lipo in and charging = )_

-Mike

[Hyena]

My buzzing ONLY came from the R37 resistor mod. The second I touched another resistor across in in parallel the current dropped and it started the arcing/buzzing sound. Remove it and the current shoots back up and the arcing stopped. The packs I was charging are also brand new, but as I said they happily charged silently at the full current output from the power supply so in my case atleast its not the packs causing the buzzing (and probably less likely in your case too, unless one cell is madly sucking current or something ? )

Oh and yeah I have the earth connected - well, the earth connector to the AC power lead earth. I haven't physically run a lead from that earth terminal to the side of the case. to the I have a CFL light over my work bench that buzzes quite loud sometimes, but a sharp whack fixes it. Hmmm, maybe I should try that with the PSU next time...

[mwkeefer]

My buzzing ONLY came from the R37 resistor mod. The second I touched another resistor across in in parallel the current dropped and it started the arcing/buzzing sound. Remove it and the current shoots back up and the arcing stopped. The packs I was charging are also brand new, but as I said they happily charged silently at the full current output from the power supply so in my case atleast its not the packs causing the buzzing (and probably less likely in your case too, unless one cell is madly sucking current or something ? )

Oh and yeah I have the earth connected - well, the earth connector to the AC power lead earth. I haven't physically run a lead from that earth terminal to the side of the case. to the I have a CFL light over my work bench that buzzes quite loud sometimes, but a sharp whack fixes it. Hmmm, maybe I should try that with the PSU next time...

Don't bother whacking, I tried it and used a hammer even ! (mostly kidding).

I had worse buzzing from the 48v unit before the current resistor mods, again I think it's the OSC rate being changed with the central voltage changing... im workin on it but I think fechter will beat me to a real diagnosis / fix.

-Mike

[Hyena]

Well my new power supply arrived today and to my suprise when I opened the case I found that it's actually slightly different to the previous one I blew up. It sounds like it's exactly the same as the one Vanquizor has, with C36 populated this time and the shunt in J3. I didnt check the R37 value but I wouldn't mind betting its lower. Out of the box the current was only 9.6 amps this time, still more than the rated but not as excessive as before. I nibbled at the shunt a bit and got it down to 9.1a and I'm going to leave it at that. That's fine for charging a 10ah turnigy pack and although they can have bulk current belted into them I'd rather keep the charge current under 1C in the interest of longevity.

Annoyingly I found SVR1 only went to 900 ohms so I couldn't go below 43v. It was marked the same value as my previous supply so I guess it's poor QC / crappy component tolerance. I replaced it with the pot from the other power supply and managed to get the voltage down to 41.6v and it's now charges happily and quietly.

On the previous topic of the buzzing, I recorded a short video incase its of any interest. The quality is pretty crap off my phone but you can make out the noise. It starts and stops because I'm just bumping another resister across R37.

[heathyoung]

Sounds like a cicada

Seriously though - that sounds like instability in the feedback loop - have you scoped the output? The frequency should be around 40Khz or so, you should never hear it, but when the frequency drops (or when you get weird harmonics) the ferrite cores 'sing' especially if they are gapped. This is a good tell-tale that the PSU is NOT happy with the load. When I was building my own, that was usually the point where my high-side switches perished, or got REALLY hot.

Have you post-mortum'ed the old PSU's? I wouldn't mind a look at some of your dead-'uns to see what happened... Adjustable SMPS'es are interesting beasts, they are adjustable upwards less so than downwards - reason being that you still have a step-down transformer with fixed winding ratios - if you have (say) a ratio of 340:15 (340 comes from the 340V DC of rectified 240V AC mains * 1.414 due to sinusoidal waveform). This gives 12V DC out easily. If you try to get 20V out - not a chance. You may see 20V at a low current capacity, due to rectified spikes/higher mains voltage locally, it will sag on load and will try to cook itself trying to get there on load.

There is some leeway (obviously) in the winding ratios to cope with output/input sag/surge etc. but there comes a point where a higher duty cycle just wont produce any more voltage.

Better to adjust down a higher voltage PSU thats close than adjust up a lower voltage thats close - you are running so much closer to the limits of design. Higher voltage down means lower duty cycle (+lower current) than it would normally run at, so more headroom when its called on 'to produce the goods'.

Best is to buy a PSU that is the correct voltage for the application in the first place

[Hyena]

Have you post-mortum'ed the old PSU's? I wouldn't mind a look at some of your dead-'uns to see what happened...

The pics I posted earlier were of the one that blew - thats about as far as I got, I didn't bother trying to test individual components. For $40 delivered it's not really worth trying to troubleshoot. If there's anything in particular you want me to test or look at though let me know. I dont have a scope or any other cool toys, just a multimetre and a few other basic bits and pieces.

I've played with the replacement some more and found that it does actually make the buzzing / cicada noise at higher current. I've got it set at 9.2a which it happily charges at silently, but when the fan kicks in the current spikes up to 10.5a and it starts chirping. When the fan goes off the current drops back it and it's silent again. As the current starts to drop off at the end of the charge it doesn't make any noise any more when the fan kicks in, so it seems to be when the current exceeds 10a it does it.

Here's a vid demonstrating the above




(real cicadas can be heard at the end )

[Tiberius]

Hi,

I had buzzing from one of mine when running it in current limiting mode. It appears to be an instability in the control loop.

I have a variable electronic load and I used that to simulate a range of load resistances. With that it was always stable, but when charging batteries there was often a stage where it went unstable, usually near the beginning of the charge. So clearly, a discharged battery isn't a linear resistive load; well we knew that, but in some cases the effect is enough to upset the PSU control loop.

In my case the buzzing was with my external current control loop, so there was the potential problem of two interacting control loops and the solution was simple. Make sure the natural frequency of the two loops are well apart. It is of course possible for a single loop to go unstable with particular loads. The fix is often dead simple, but it really requires knowing the circuit to find out which are the dominant filter components.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=6749&p=209094#p209081

Nick

Edited to add: A battery has some of the characteristics of a capacitor, and designing circuits to drive capacitive loads is a well known problem. From the point of view of stability, a capacitive load is the worst thing to hang onto a circuit with a feedback loop.

[Hyena]

Cool, I missed that part of the other thread, I'll have to try adding a cap and see if that works.

In the mean time, it just isn't my week, I just had another SWPS go up in smoke in a fashion that could only be described as truely epic!
At first I thought it was my lipos going up and was about to exit stage left at a rate of knots but then I realised the smoke was pouring out of my charger.

This one was a 24v 'JAE' brand and has been performing well for months as my every day charger. I have it set to 20.7v and charge up my 15S pack in 3 parallel banks of 5S. I have a 6 pin anderson plug on the battery and one lead for charging in parallel and another for discharging in series which is connected to the bike so it's almost impossible to get it wrong. However... to cap off a bad week, my bike frame snapped a few days ago so I stripped the bike and have it in pieces in my workshop. I'm used to the series discharge plug always being fixed to the bike so didn't even think when I plugged it in and sent 60v odd backwards in the charger. It wasn't turned on or plugged in but that didn't stop it. I've never seen so much smoke come out of an electronic device that wasn't actually on fire! When I opened it up I found the 2 caps at the front had blown, covering the most of the board in 'capacitor juice'. They are only rated at 36v so not suprising they blew with 60v.

Does anyone think they alone would have been taken out ? Nothing else looks phyically damaged. If it's likely just them that have popped I'll replace them otherwise I'll scrap it.

Also for the sake of documenting different board layouts - this is the 350w 24v JAE.
The board is quite different to the meanwell and the other clone I have. The obvious differences at a glance are only 2 caps up front with only an unpopulated 3rd (vs the others that have 4 or 3 with the 4th unpopulated), there's 2 big transistors heatsinked to the case up front, vs the others that only have 1 and other components are in different locations or absent.

[heathyoung]

$40 delivered? Who is your source - computronics want more than that...

[Hyena]

Yeah computronics charge like wounded buffalo's. I'm all for supporting a local business/importer but when they're triple the cost it's a bit hard. Although if you really want a giggle try pricing them at jaycar!

I've had a few now, but my latest ones I've been getting and posted about earlier are from here:

http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWNX:IT

The seller is very reasonable too, I had one arrive with a dead fan and although it's an easy fix I thought I'd email them to see what they said. I expected them to say they'd replace it if I sent it back (at which point I'd go down the street and buy a fan for $5) but instead they replied 10 minutes later with "we'll send you another one" and a week later it was on my doorstep. I didn't feel so bad when I blew it up a day later (although maybe it blew because the fan wasn't the only problem with it ?)

If you want a genuine meanwell they're $58 delivered from sure electronics (which is still cheap)
http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWNX:IT

[mwkeefer]

Hey all,

Sure-electronics is a good spot to get the meanwells and if you order enough (5+) the price comes down a bit and S&H is reasonable.

Just in case anyone cares.. I toasted an alligator clip tonight... my parallel adapter on the positive side I had to use black shrink wrap on and I knew the moment I built the pack that it was a potential disaster waiting to happen... the good news, the supply and packs are fine and though I had blackened my fingers I suffered no burns. My son was on the other side of the room and it even served as a good teaching example of why he isn't allowed to touch daddy's stuff when I'm asleep. All in all it was a single Female 4mm gold connector and the tip of the aligator clip that vapoorized in my hands - I love indoor fireworks.

About the buzzing... I don't have a scope worthwhile enough to measure the OSC of the various portions of the PCB but I know a few guys out here who do.. I have managed to nearly eliminate buzzing in my 48v to 63v covert model... the trick was not "EXPANDING" the range but moving the range up. Once I re-populated the voltage regulation resistor network with values to give me roughly 55-65v of output (zener limited and tested to 63v) so I keep the same basic "range" just move it up the voltage spectrum. I think nick is right though, that it is because of the two limiting functions of the supply working at too close a frequency... I just don't have any viable way to test.

The current jumping (or peaks) when the fan comes on is exactly what I explained previously - when the fan kicks on, it draws power from the same isolated and scaled voltage power source that the TL494 uses... this additional current draw causes the voltage being supplied to the DTC (Dead time control) to drop. This pin works in INVERSE mode so 0v input = MAXIMUM CURRENT, 3.3v on the pin = 0 CURRENT. Since the additional load of the fan causes a voltage drop, that is the reason the current spikes up when the fan switches on.

I've solved this problem in my own units by building a small internal supply (which uses the output voltage as a source) which is wired up much the same as the Infineon ANY VOLTAGE modification to an LM317 and outputting 12v (very little current). Since this is pulled from the main outputs instead of the logic VCC bus... there is no drop on the DTC pin with the fan running... this means a flat curve without the peaks.

I will share the schematic once I have any issues worked out.

Hope this helps!

-Mike

[Tiberius]

The current jumping (or peaks) when the fan comes on is exactly what I explained previously - when the fan kicks on, it draws power from the same isolated and scaled voltage power source that the TL494 uses... this additional current draw causes the voltage being supplied to the DTC (Dead time control) to drop. This pin works in INVERSE mode so 0v input = MAXIMUM CURRENT, 3.3v on the pin = 0 CURRENT. Since the additional load of the fan causes a voltage drop, that is the reason the current spikes up when the fan switches on.

I've seen a similar effect on my ones. The parameters change slightly when the fan goes on or off.

But....I decided to live with it. We're trying to make battery chargers here. If I were building a supply to power some sensitive electronics then I'd be doing things very differently. What led me to these PSUs was not their performance in terms of accuracy or noise, but simply the W/$, W/Kg and W/cuft.

Nick

[mwkeefer]

Nick,

For my own personal use... I am in 100% agreement with you, just use them with proper nominal current output and the voltage needed. I thought it a good idea for others if I test and push this on all fronts, trying to make it perfect.

Personally... I've been linking a pair of voltage modified 24v units for a 650w nominal charge into a 10A pack of 15s, this works out to a bit over 1C. My only concern here (and why I got into the fans in the first place) is that running close to maximum ratings is bad enough but add an amp overage (it's roughly what type of jump I was seeing) and things could get really bad, really quick - imho.

These things are great for the w/$ - even with the ones I've sent out to various people (gratis) and blown up, I've still paid less for these all together than for 2 iChargers (without DC supplies or S&H). What I have ended up with is one portable (semi?) 5 - 7.5A charger (10-15S) and a set of "base station" chargers one for 10A @ 15S charging (1C) and the other for 2C or 20A charge of 15S (yep, 4 supplies in series / parallel and trimmed to 300w each nominal).

I can't tell you how freaking cool it is to be able to load up my 15S2P to 90% within 20-30 minutes!

Again thanks to you, Fechter, Jermey and Methods (I'd not have gone this way without you guys!)!

-Mike

[Vanquizor]

With the concerns about instability with the fan cycling wouldn't the quick and dirty be to just force the fan to run 100% of the time? Would still give predictable output and it can't hurt life cycle to keep things a little cooler.

Suggestions on the best way to accomplish this?

[Hyena]

This was mentioned earlier, either find 12v on the board on use a small phone charger or similar, powered off the same AC input but running the fan seperately.

I agree with Nick too, as battery chargers they don't need to be uber precise to the 10th decimal place and they're pretty good as is. I doubt a few spikes as the current tapers off is going to be the end of the world and drastically reduce pack life.

Also, I managed to repair my other supply I blew up the other day. The blown caps were 2 35v 2200uf units and I replaced them with 2 63v 1000uf units from my dead 48v supply (nearest match I had around) I was tempted to fit an additional cap to the spot along side that was previously unpopulated (given the original units were 2x 2200uf and I only replaced them with 2x 1000uf) but after a 10 minute test it seems to be ok so I'll leave it alone.
So I guess that's handy to know - if you happen to be a dumb ass like me and have a lapse in concentration that sees you connecting too high a pack voltage, it's only those caps at the front that will blow.

[mwkeefer]

Hyena,

12v on the board is the logic supply rail... that's what is being tapped now and would cause the same issue.

The 5v-12v supply (wall pack style) is fine... but I want to continue researching and testing, refining which includes a very simple 12v regulated supply drawn from the output stage... it's a few resistors a diode and a LM317 and can source up to 1A if needed. Also very efficient and tiny enough to be installed inside each unit.

While I agree with you both, peaks to the packs won't matter but... peaks for the supply when already configured for 350w continuous output power push up over 480 and without initial current reduction were approaching 10A (that's 580w output)... that was without a peak caused by increased load on the 12v internal rail...

Im sorry but until someone here corrects me with regards to my estimation that these supplies should last quite a while with proper power limiting and fan not driven by the internal logic 12v bus, but if just run silly nilly (it takes an hour of continuous operation to charge in many cases) they will surely give up the white puff in short time.

Please do correct me if I am wrong or someone has experience with this... I am basing this on my own experiences and also the specs of the most probably points of failure (transformer, FETs, Diode, Caps).

*With that aside, I'm curious and would like to ask the experts a question...

As everyone knows some models (more recent) of the 350 have an unpopulated section of the PCB just aft of U1 (TL494CN)... In reviewing this circuit, I understand how 1/2 of it works but I am at a total loss for the purpose of the second half. A bit more specific:

If R33 is removed from the PCB and R37 is populated in addition to SVR2 it forms a variable current or adjustable current feedback loop.

The part I just for the life of me don't understand (read that as I'm not sure what value components to install here) is involving D18 and Q7. In my conversations (limited as they were, the tech guys at meanwell are awesome - sales at Meanwell USA isn't even worth bothing with and I was inquiring with regards to 1000 unit purchase, the sales biat** referred me to mouser who had 2 in stock?) with Meanwell tech, he was very hesitant (I think he could get in trouble) but at least informed me the transistor is of type NPN.

I have the main parts were interested in (opamp, shunts, voltage reference and current reference) in schematic form and I'm just in the process of double/triple checking I didn't miss anything important (Like as if I know what important is) - once I've verified them I'm happy to post but I just thought maybe one of the EE or just all round geniuses could figure out the purpose (if they have a model with missing parts on the PCB).

Thanks in advance!

-Mike

[fechter]

The part I just for the life of me don't understand (read that as I'm not sure what value components to install here) is involving D18 and Q7. In my conversations (limited as they were, the tech guys at meanwell are awesome - sales at Meanwell USA isn't even worth bothing with and I was inquiring with regards to 1000 unit purchase, the sales biat** referred me to mouser who had 2 in stock?) with Meanwell tech, he was very hesitant (I think he could get in trouble) but at least informed me the transistor is of type NPN.

-Mike

As far as I could tell, that was some kind of backup overvoltage protection. If D18 is a zener and it turns on Q7 above a certain voltage, it can pull on the same op amp that the current limiter does and turn down the duty cycle.

[mwkeefer]

With the concerns about instability with the fan cycling wouldn't the quick and dirty be to just force the fan to run 100% of the time? Would still give predictable output and it can't hurt life cycle to keep things a little cooler.

Suggestions on the best way to accomplish this?

Not sure how I missed this post... but your right, if we enable the fan by default... the load to the circuit will be constant then we just adjust for the new offset in the R33/R37.

I'll try this in the morning...

Right now I have replaced R33 with a piece of perf board holding 2 100 ohm resistors (about 196 ohms) in series followed by a 100 ohm 10 turn pot. The factory value was 360 ohm on this 48v unit. This gives me a wide range of currents but I detect noise in transformer next to the case mnted diode... Funny part is, in most cases... adjusting the current up a turn removes the noise. The only issue here is that I didn't even run the fan (had the case open and a huge house fan going full clip on it) and was maintaining 450+ watts but the noise would dissappear for a while then creep up again (not nearly as bad) as the pack voltage climbed (and I suppose the resistance of the load, since the Ri should increase as they become full right?).

Additionally I replaced R25 with a 15k and SVR1 with a 1K 10 turn, in addition to the 1K... i tagged another POT on top of SVR1, a 100 ohm 10 turn for fine adjustments (now I can keep steady voltage between 62.25/62.27).

Maybe I should just replace my R33 variable circuit with a single 260 ohm precision (1%) and a higher precision 10 turn 100 ohm pot in series. If I leave that calibrated for 360 ohms (where R33 was) I can adjust from 260 ohms up to 360 ohms to give myself a taper (as I have now)... then remove the thermistor style fan control and replace with just simple voltage divider calculated to provide 2x the current required to run the fan. My bumps in current amount to approx 1A when the fan goes active - my existing adjustment circuit (200 ohm + 100 ohm pot) would manage just fine tapering to account for the draw from the fan load. I think the existing fan is 22ma or somthing (been a while), can't exactly drive a CPU or Case fan from that (22ma @ 12v) but... I suppose if that little fan they come with were on all the time and the components are properly sinked to the case (ie: artic silver on both sides of silicone spacer pads) then the temperatures would stay pretty darn low.

I have yet to try to move any of the caps around... I'm still trying to wrap my mind around it.

-Mike

PS: anyone tried any SICK voltage mods yet, ie: 72 or 83 or 88 or higher with these?

[fechter]

Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far. A sidestep approach is to simply use two or more supplies in series to get the desired voltage. With two in series, I suspect you could get away with just keeping one stock and mod the current limit on the other one. The one with the lowest limit will do all the limiting anyway. You may actually need to turn down the voltage on one in this case to get what you want.

[Hyena]

Mike, I picked up some 1k, 2k and 200 ohm 10 turn pots + a handful of 100 and 200 ohm resistors yesterday afternoon to do pretty much the exact thing you just described! I was just going to put the 2k in svr1 to allow the voltage to go a bit lower. What was R25 before you changed it ? Mine is 22k I think. If yours was the same and you've dropped 7k that sounds like a fair bit (assuming your R25 is in series with SVR1) Or is this big drop what's enabling you to go to 63v ? (plus upping the zener under the transformer of course).

As for higher voltage mods, if the transformer is even up to it you'd have to swap out the front caps atleast. Mine are only 63v units so you're running right at the upper limit of what the 48v models can do.

Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far

I don't think so Fechter, at least not completely. Mine has all the same symptoms Mike is describing and unmodified it's running at the lower end of its range (42v on a 48v unit)

[mwkeefer]

Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far. A sidestep approach is to simply use two or more supplies in series to get the desired voltage. With two in series, I suspect you could get away with just keeping one stock and mod the current limit on the other one. The one with the lowest limit will do all the limiting anyway. You may actually need to turn down the voltage on one in this case to get what you want.

Wouldn't the "correct" way to do this be, connect 2 in series (each of higher than 1/2 required voltage nominal so for 62.25 - 96v use 48v units) and then configure so each is identical in voltage first? Then adjust one of the 2 units to limit the PWM or current output?

I've tried that too... honestly the noise I'm getting now is different than the cicada noise everyone (including me) have been pointing to, it is much more subtle humming or buzzing and really i need to quiet all else in the room to hear it. The same humming occours when I put 2 48v units adjusted for 31.125 each... regardless of power levels I run them at (R33 mod limits).

So I think by moving the voltage range instead of just increasing the range helps and gets me/us closer to a well working charger...

Here is an graph of the 6.7mi WOT (40mph max) discharge trip:


Here is the charge plot:


Balance was nice at C/20 the pack was within 5mv (4.155 - 4.150).

The maximum temperature of the charger FETS durring operation was 89 F (not bad given an ambient of 72) - Probe attached to outside of heatsink portion of case... arcticsilver compound for better readings.

The buzzing or humming was adjustable out (a little tweak to the resistance of the current limit - silent after first adjustment to 7.02A) until the CV phase cross over point then I could hear the hum (nothing like before) until the current dropped below 6.8A (when I configured for flat 6.8 A, the hum is still present but lower down the voltage range and actually dissappears before CC/CV cross over).

Back to the refinements for tommorow... I will have a nice 6 or 7A portable charger if it kills me (it may).

-Mike

[mwkeefer]

Mike, I picked up some 1k, 2k and 200 ohm 10 turn pots + a handful of 100 and 200 ohm resistors yesterday afternoon to do pretty much the exact thing you just described! I was just going to put the 2k in svr1 to allow the voltage to go a bit lower. What was R25 before you changed it ? Mine is 22k I think. If yours was the same and you've dropped 7k that sounds like a fair bit (assuming your R25 is in series with SVR1) Or is this big drop what's enabling you to go to 63v ? (plus upping the zener under the transformer of course).

As for higher voltage mods, if the transformer is even up to it you'd have to swap out the front caps atleast. Mine are only 63v units so you're running right at the upper limit of what the 48v models can do.

Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far

I don't think so Fechter, at least not completely. Mine has all the same symptoms Mike is describing and unmodified it's running at the lower end of its range (42v on a 48v unit)

Actually... my 48v units come with 100v caps on the output already (sure-electronics) so they can handle it... the PCB is stamped with a 94-0V which in chinese means 0-94V output. This just means the design can handle it... I haven't measured the voltage output at the transformer taps on these units yet (I need to though) and I am going to stick a temp probe on there tommorow too (SNOW DAY, LOTS OF CURRENT DUMP).

One thing I did note... if you look at Meanwells specs (Like they are useful for anything) the higher the voltage, the more efficient the unit... I wonder if they don't source with transformer at high end range and tone it down? Tommorow.

My unit was different, R25 was 2k I think... I don't remember anymore = )_

But you have the relationship correct, lower impedance on my R25 (in series with SVR1). With the stock 1K pot... the extremes of range were:

Testing minimum output: 39.1v @ 2.82k
Testing maximum output: 58.1v @ 1.92k

And the voltage wasn't very steady..

(I did add a 5v zener to the stock 62v unit that came with my chargers...)
By using 1.5K + 1K pot + 100ohm pot... new maximum impedance is = 2.6k (so only 400 ohms or so lower than the default)... by default I could tune up to 58v so I needed just a little lower impedance in the range...

Rough low range is now 1.6k but the 1K and the 100 ohm were started dead center of 10 turns... so the outcome was tuned (before power up) to the midrange value of 2.050 K

I lost a bit of low end (more than I had planned)... I expected to have dial in between 41v and 63v but overshot the low end a tiny bit (not enough resistance to get the range low enough) but with the main SVR1 + the 100ohm trimmer... I'm getting much more stable voltage output (+- 3mv)

One last bit.. tommorow I'm replacing all my resistors in the voltage and current reference and adjustment circuits for 1 and 2% types... I think this may solve the remaining fluctuation with the output... if not, I will add more 100v caps.. lower ESR... that should flatten the output.

When I have all this "figured out" I am thinking that I will just setup a switch to select what voltage range I want (ie: 40-42, 49v-50.4, 61-63v)... once I see how stable I can get the voltage using better resistors in the network... I will look into configuring these as "chargers".

I'm thinking a 3 power level switch might be good also (400w, 350w and 100w)... this would be useful for bringing stubborn packs into balance over a longer charge curve.

Oh well... I'm rambling, I'll look at your PCB pics in the AM and figure out what points to check for impedance... then we can bump the unit either way or just expand the range.

-Mike

[mwkeefer]

One last bit...

Hyena - if your stock R25 is 22K then assume approx 23K max range with SVR1 existing... Just lift SVR1 pin #3 and wire up one of your 200 ohm pots in series (off pin #3, the independent unjoined pin).. that should increase the low end by about a volt or so.

Hot glue is your friend. These tiny 10 turn pots aren't stable just soldered into position with the legs bent, I find that mine are much more stable and user friendly once you add gobs of hot glue around them (not where the wires are or under, but around). You can always seperate the glue and it does a good job of holding things steady.

If you want to add a "fine tuning" adjustment... adding a smaller value (100, 200, etc) in series with SVR1 will give you minute adjustment (100 ohms / 10 turns = 10 ohms per turn) and you can just stack it ontop of another 10 turn but with the adjuster screw opposite. I will post pics tommorow when I can get to my camera.

-Mike

[Hyena]

Actually... my 48v units come with 100v caps on the output already (sure-electronics)

Ah ok, that's another difference in the cheaper knock offs then.

My unit was different, R25 was 2k I think... I don't remember anymore = )_

That's exactly why I take pictures of everything before I pull it apart
Mind you, taking lots of photos didn't stop me having 2 left over bolts and a broken tensioner the first time I swapped the camshaft in my car...

I'll look at your PCB pics in the AM and figure out what points to check for impedance... then we can bump the unit either way or just expand the range.

Don't spend too much time on it, I have a meanwell on the way from sure electronics that should be here in a few days - that's the one I'll do all the modding to so it should be exactly the same components and values as what you're using.