Switch mode supply mod

[SpeedEBikes]

I bought a Meanwell S-350-48 power supply through Sure Electronics off EBay.

After waiting about a month for the slow boat from China, it arrived yesterday and I wired it up. I'm using it to charge 12 s (by 15 AH) lipo packs. On first try it was running hot pushing 9.5+ amps and 450+ watts. After reading online I opened it up to adjust the shunt. The shunt had 3 loops. I expected that just clipping one loop would result in roughly a 1/3 reduction and put me at about 300 watts. I wanted to be a little closer to the 350 rating, so after clipping one loop in the center I bridged one of the clipped legs part way down to an adjacent loop wit a blob of solder.

On my second test, I was delighted to see it pushing 348 watts. After about 10 minutes the fan kicked on. And when it did the current shot up by almost an amp and the unit was pushing about 400 watts. Also, in addition to the fan whir, simultaneously a fairly loud high frequency (a couple hundred hz?) popping sound starting coming out of the unit. I disconnected the charging battery and the popping sound stopped though the fan continued running on for a while so I know the sound isn't the fan. When I unplug the power supply it sits quietly for a few seconds and then as the green led starts to fade the supply also emits a similar popping/ticking sound. However, in this case the sound slows and diminishes away over a couple seconds, while when the sound happens while charging with the fan on it is loud and fairly steady.

Any thoughts about this sound? Or about the surge in output current when the fan kicks on?

 

[dozentrio]

The ominous buzzing has been mentioned a few times in this topic. Consensus seems to be that it's ok, and you can safely ignore it. On mine, the buzzing happens whenever its the power supply is working at full load. When you reduce the max limit by modifying shunts or other methods, the buzzing will happen at this new limit you've set. As soon as your pack is nearly full and it starts charging at slightly less than max power, buzzing stops. I'd like to make it not do that, as I plan on charging my pack in coffee shops as I sip coffee and read. And of course, the other customers won't be impressed with the noise. So far, no solution has come to mind though.

 

[mwkeefer]

First - mod your fan by replacing the thermistor with a resistor... I don't recall the value however I can tell you the higher the voltage output of your supply (if you did modify the range) the faster that fan would spin... What you want is a resistor which will cause the fan to come on upon startup... I think I used 4 100ohm resistors in series but I can't recall.

Once the fan mod is done, then modify the current... I have decided the shunt method is useless in many cases (especially with the fan mod)... in your existing setup - when the fan kicks in, the input voltage rail of the TL494CN PWM IC regulator and more specifically the current limiting PWM is effected by this drop in "bus voltage".. doing the fan mod first ensures when you next calibrate the output current... it will remain stable.

Now for the output current... I have had good results with the resistor mod (R37 or R33 - can't recall but search this thread) .. by reducing it a tad (I think stock resistor is 330 ohms) you will lower the current and yes that buzzing / frying sound is somewhat normal... with the fan on all the time, not only does the unit stay much much cooler but you can't hear the annoying buzz...

For the real deal: I remodified my S-350-48 and removed the resistor based current limiting and restored the stock resistor, I thought cutting a shunt would do the trick however... My results were not as expected, now my Meanwell puts out approx 7.2 - 7.4A constant current mode up to 62.25 - 62.70v (depending on my mood) and maxxes out between 460 and 480w (it actually holds between 7.4 - 7.2A right up until about .75 - .50v from cutout voltage I have set then it does begin to taper naturally... I think there is some maximium limiting which is overriding in these which keeps them at no more than 460-480w.

The BEST PART - I have measured my newly remodified charger over about 90 cycles and guess what, even at this extreme output overdrive... the darn thing stays relatively cool (with the fan on all the time)... the only other mod I made was to replace the silicon sleeves with a better thermal conduction and added arctic white grease to the case sides...

If I mount one of these on my bike (it will be on the full size and mounted beneath the rack) - I will full enclose it and ensure multiple points of metal to metal contact to assist in heat dissipation! I am concerned with vibration causing ill effects but I could waste 1 and anyway I carry mine around with me now in my bike trunk.

I am not advising you do this but... it is working for me, now I just need good balancing (3 of the GGoodrum HK Balance Extenders would work but I find the margin of error in calibration on these units - atleast the display voltages leave somthing to be desired)

Hope this helps!

-Mike

 

[Hyena]

First - mod your fan by replacing the thermistor with a resistor... I don't recall the value

500 ohms and this will make the fan come on at start up. If you go too low the unit won't power up at all (it thinks it's overheated from the resistance it's seeing from what should be the thermistor) I can't remember the resistance of the thermistor off the top of my head but it was around 1 - 1.5k at room temp and the fan kicked in when the thermistor resistance dropped to around 800k. I have another idea but it isn't really necessary for me as I have an ammeter on mine to keep an eye on the charge. In the absence of an ammeter or some other method of monitoring current flow though you could add a resistor in parallel across the existing thermistor - this would make the fan kick in earlier but still turn off when the the temperature got close to ambient. When the fan switches off you know the charge is done (or nearly done) Off the top of my head you'd probably want something along the likes of a 2 or 3k resistor, but throw in a 5k pot and you could set it to kick in at what ever temperature you wanted.

 

[mwkeefer]

Hyena.. when my pack reaches the CC/CV delta and then the current tapers to nothing... the fan does shut down and the output goes off - no current flowing at the end and fan indicator.

I have a Watts Up meter attached to my Meanwell which allows me to "tweak the output voltage" which sometimes I must do based on ambient temperature but it's rather simple to double check before plugging in the bulk pack.

I'll rip my meanwell down again tommorow to get the value for the fan resistor mod I did (and the stock R33/R38).

-Mike

 

[SpeedEBikes]

Thanks for the suggestions!

I ran the power supply with the lid off to see if I could tell what was buzzing. I wasn't able to cleanly isolate it, but if I had to bet I would say it is the big coil/transformer in the square frame. I think it is getting duty cycled at an audible frequency. By pressing down on each of the corners I was able to vary the buzz sound. I then found that the 5 screws mounting the PCB to the chassis were all a little loose and tightening them seemed to reduce the buzzing slightly.

Since the buzz is typical I'm not going to worry about it too much more but I was bothered by the output jumping up about 10% when the buzzing occurs. Since the supply is rated for 350 watts I don't want it exceeding that. So I unsoldered my shunt bridge on the cut shunt. Running with just two of the 3 shunts I get about 315-320 watts from the supply.

At that power level after about 15 minutes of use it still hadn't heated up enough to kick on the fan and resume buzzing. So I put a hair dryer on it until it kicked in. The power again surged but this time only up to about 350 watts. I'm hoping now that I've read the replies about the always on fan mod that doing the thermistor/resistor mod will have the supply running at a steady 350 watts.

I also want to be able to sometimes toss this in my bag when I go for longer trips. I've been doing that with a much more expensive iCharger and 15 volt supply, but I don't need balance charging on the road. I don't need to have a charger permanently mounted on my bikes as I typically take my batteries off my bike and bring them into my basement while I leave my bikes parked in a garage. The insides of the charger seemed reasonably vibration proof. There are generous globs of goop stabilizing the big caps. Are there any other parts that would benefit from a similar treatment and if so, what kind of goop/glue is best?

 

[cell_man]

From what I understand these PSUs can cause some issues due to the fact that they do not reduce the current as the voltage approaches the set voltage like a normal charger would do. The typical BMS is just not suited to this and it doesn't stand a chance trying to shunt the 5, 10 or whatever amps the PSU is set to. I was thinking that a suitable series resistor in line could accomplish this current tapering as the PSU reached it's set voltage. You would of course loose some efficiency heating the resistor but it's not the end of the world IMO. By adjusting the resistance you could taper the current off as required and it would still charge the pack fully.

What do you guys reckon

 

[SpeedEBikes]

Cellman,

There is no issue with the charge profile of these supplies.

People should know what the ratings of their packs are with respect to both charging and discharging and select a charger/supply that falls within those specs. These supplies are somewhat adjustable for both voltage and current so they can be tailored for use with many packs.

I'm not using a BMS. I use Junsi celllogs as monitors, set conservatively, and connected to very loud alarms. Thus long before anything goes significantly wrong I know about it and can manually intervene. Balancing is rarely needed and when it is I use a balancing charger.

A CC/CV charging profile is all that is needed for lithium rechargeables. No tapering is needed at least so long as one is charging within specified rate and voltage. In my case I'm using the charger on a 15 ah pack of cells that are spec'd for up to 2C charging (ie 30 amps). I'll be running this psu at roughly 7 amps so no futher current reduction is needed. Finally, because it isn't a balancing charger and because I typically prefer to under charge my cells for pack longevity I'll be using termination voltages of between 4.05 and 4.15 volts per cell and normally toward the lower end of that.

BTW, I suspect that most folks who report tapering with chargers actually have cells with fairly high IR. Thus the charger hits CV earlier then they are expecting and current tapers off. If one wants to guarantee current tapering earlier, instead of adding additional resistance one can simply lower the termination voltage.

 

[cell_man]

Yeah but you're using LiPo going by your cell voltage and that does stay very well balanced. LiFePO4 doesn't stay so well balanced and I'm thinking more about the typical off the shelf BMS that has less than 100mA shunt current. I've checked the chargers I have and they throttle the current back as the voltage reaches it's max voltage and these aren't high IR cells. Tapering the current gives the BMS a chance to balance the pack, otherwise it will just go HVC.

 

[SpeedEBikes]

Yeah but you're using LiPo going by your cell voltage and that does stay very well balanced. LiFePO4 doesn't stay so well balanced and I'm thinking more about the typical off the shelf BMS that has less than 100mA shunt current. I've checked the chargers I have and they throttle the current back as the voltage reaches it's max voltage and these aren't high IR cells. Tapering the current gives the BMS a chance to balance the pack, otherwise it will just go HVC.

Current is simply voltage divided by resistance. A charger maintains constant current by adjusting the voltage to the load. Once it has reached max voltage it is no longer controlling the current. Then it is the load that is 'controlling' the current.

If someone pairs a low current BMS with a high capacity pack, LiFePO4 or any other chemistry, then they are asking for trouble, either slow or incomplete recharges. The problem isn't with the charger but with a poorly chosen BMS.

 

[number1cruncher]

My S-350-48 tapers very nicely near the end of the charge cycle, once the set voltage(50.04 total, 4.17 per cell for a 12S3P) is reached. It will charge at <1A for a while, allowing my balancers to smooth the cells out. I am also charging LiPo, but I wouldn't think battery chemistry would affect the charger's(SMPS) charging profile.

 

[SpeedEBikes]

My S-350-48 tapers very nicely near the end of the charge cycle, once the set voltage(50.04 total, 4.17 per cell for a 12S3P) is reached. It will charge at <1A for a while, allowing my balancers to smooth the cells out. I am also charging LiPo, but I wouldn't think battery chemistry would affect the charger's(SMPS) charging profile.

It's not your charger doing the tapering. The charger is merely holding a fixed voltage. The tapering is a function of your batteries (and BMS if you have one). Quality cells in good shape will have low internal resistance and will taper off quickly. With older cells or low quality cells the current will taper off much more gradually. Also, LiFePO4 cells have a very non-linear voltage response to state of charge. As they approach full charge their voltage rises very rapidly. This characteristic can make LiFePO4 packs appear more unbalanced then they really are at end of charge. With a higher termination voltage, say 3.60+ volts per cell it can also make for a fast taper cut off, especially if the pack is in good shape and well balanced as all of the cells hit that fast ramping voltage together.

 

[cell_man]

Yeah but you're using LiPo going by your cell voltage and that does stay very well balanced. LiFePO4 doesn't stay so well balanced and I'm thinking more about the typical off the shelf BMS that has less than 100mA shunt current. I've checked the chargers I have and they throttle the current back as the voltage reaches it's max voltage and these aren't high IR cells. Tapering the current gives the BMS a chance to balance the pack, otherwise it will just go HVC.

Current is simply voltage divided by resistance. A charger maintains constant current by adjusting the voltage to the load. Once it has reached max voltage it is no longer controlling the current. Then it is the load that is 'controlling' the current.

If someone pairs a low current BMS with a high capacity pack, LiFePO4 or any other chemistry, then they are asking for trouble, either slow or incomplete recharges. The problem isn't with the charger but with a poorly chosen BMS.

We'll just have to agree to disagree and thanks I know Ohms Law

From what I have seen many chargers will reduce the current as it approached the max charge voltage which will give the BMS a chance to balance the cells and prevent any hitting the HVC. The only BMS that I know of that throttles the charge voltage back to allow the cells to balance is the Ggoodrum BMS which does this as the first cell reaches the Balance voltage to prevent the charge current from overloading the shunt current capacity. This function was included to allow the BMS to be successfully used with a simple PSU rather than a more expensive charger. Most BMSs that are in use have lots of assumptions made when they are designed such as a charger that tapers the current and perfectly balanced cells with equal capacity/IR. That's why they have settings such as 75mA shunt current, 3.7V shunt voltage and 3.9VHVC on a 15A max charge rate BMS. Using a PSU with 1 of these will not damage the cells if they become unbalanced but it will likely cause the BMS to disconnect the charge voltage repeatedly whilst the cells hit HVC of 3.9V and then connect it again when they drop to 3.8V.

All I'm suggesting by putting a series resistance in line is that when the charge voltage gets within say 1 or 2V of the required max charging voltage, it will cause the charge current to slowly taper off until it reaches the max charge voltage. Not saying it's absolutely necessary just thought it could work in some situations. The more series cells that are charged the more important it is to pay attention to the charge current as it approaches the max charge voltage IMO.

 

[chroot]

How many lipo 6s pack can charged by meanwell's 350 watts. I cant find the formula math that calculate per watt on each 6s pack. I am planning charge 16 of the 6S pack in parallel (88v nominal 20Ah). I am not sure if 350 watt is enough for whole 16 at once charge.

Any cheap meanwell switching power supply. Mostly I see over 50 dollars on ebay. Which one is original meanwell due too many
clones chinese meanwell. I am looking for 24V DC 14.6A 350W Meanwell Switching Power Supply. Let me know

 

[GGoodrum]

Actually, the only difference between a multi-profile charger and a typical "switched"supply, when used as a charger, is that the charger has more than one constant current (CC) limit. The CV mode works exactly the same. All both do is limit the current to whatever it has to, using a PWM circuit, in order to keep the total pack voltage at the set limit. It doesn't know or care what the individual cells are at, as it only "sees" the total voltage. With unbalanced cells, you can have some very low, even zero, and some very high, and still have the total pack voltage at, or under, the CV set point. What some "BMS" designs do is simply cut off the charge current completely once any cell hits the HVC point. The problem is with really unbalanced cells (or cells with significant capacity differences...), the high one will hit this HVC point way too early, if the supply/charger is sill in the full CC mode, supplying the max current. Two things were done to try and get around this problem. First, the set point for the HVC was raised, so the high cell would be allowed to go quite a bit higher before it would trip the HVC signal, and shutoff the charge current. The second thing that was done was a second, lower CC limit was added to the "charger", so that when the total pack voltage reached a certain voltage, the CC limit was dropped. This would allow more time until the high cell would hit the HVC point.

Our design is a lot different. The HVC set point is kept low (3.62V for LiFePO4 and 4.16v for LiPo...). Instead of simply using the HVC signal to shut off the charging, we use it to control the duty cycle on our own PWM circuit, which is pretty much just like the CV mode logic in the supply/charger. The difference is that instead of using the total pack voltage to control the PWM limiter, each individual cell's voltage is used. The net effect is individual cell CV modes. In operation, the charge controller and supply/charger's CV mode logic work seamlessly together. If the cells are reasonably well balanced, the supply/charger's CV mode kicks in first, and the current starts dropping. When it gets down to around 2A, the charge controller logic kicks in, and the current continues to drop at the same slow rate. If the cells are farther out-of-balance, the charge controller CV controls will kick in earlier, maybe even before the supply/charger one does, but the drop in current goes on at the same slow rate. The point is you don't need a fancy charger, with multiple current limit profiles. As long as the supply has a CC mode, in addition to the always present CV mode logic, there is absolutely no difference between such a supply and a dedicated charger.

The whole reason for this thread in the first place is that we found many really inexpensive supplies, that could be used as chargers, but they don't have the right sort of current limiting required. Many of these inexpensive supplies do have CC modes, but are used in applications such as audio amplifiers, where they might see high peak currents, but overall the average current stays under the power level the supply is rated for, so the current limit is set to 125-130% of the rated value. This is not good for our charger application, because the unit needs to supply the current continuously at its rated output, so the current limit needs to be set to 100%, not 130%. Several clever folks here figured out relatively simple hacks to these inexpensive Meanwell supplies, to "adjust" the current limit, but it turns out there are many different "flavors" of the PCB layouts for this design, so the hack for one, wouldn't be the same for another. Compounding this issue it was discovered there are several Meanwell models that don't have any sort of secondary current limiting at all. Instead they have what is called a "hiccup" mode on the front-end that cuts power for an overload condition, and then after some period of recovery, restores power. This makes these type of supplies not "hackable".

The latest version of our charge controller now includes an adjustable current limiter, so now any of these supplies, even the ones with just the hiccup mode overload protection, can be used as chargers. The CC mode and individual cell CV modes are totally contained in the charge controller.

View attachment Simplified Charge Controller-v.4.0.6-02.jpg
View attachment LVC-HVC Charge Controller Connections-01.png

The Wattmeter is not required, but I like to use one to monitor how much goes into the pack, etc. You can actually tell where the charge process is at, simply by watching the single LED on the charge controller. It starts out red, during the CC mode. When the individual cell CV mode "throttling" starts, the LED will be orangish. As the current tapers off, as the cells get full, the LED color will smoothly transition to green. When the current drops down to about 180-200mA, the LED will be fully green, and when the current drops below 180mA, everything shuts down.

The illustrated configuration above is really more applicable for LiPo-based setups, made using the Turnigy and Zippy RC-type packs, from HobbyCity, mainly because they stay extremely well-balanced and maintain closely-matched capacities. With these types of setups, balancing is just not required anywhere near as often, so the shunt-based balancing circuits are omitted. For setups that require more frequent balancing, the full BMS, with the balancing circuits included, makes more sense. The latest 4.0 version of our BMS includes the same charge controller circuits, but adds a timer logic section that allows extra time for balancing, before shutting down. This timer can be set from 30 seconds to about 4 hours.

Anyway, the point of all this is to show that there is nothing "magic" about a charger. It is simply a power supply with CC/CV regulation.

-- Gary

 

[regmeister]

deleted

 

[GGoodrum]

Hello Gary,

What is the maximum current for the charge controller?

Thanks,
Richard

Just as in the "regular" BMS, there are two IR4110 FETs in parallel, so theoretically the current limit could be well over 100A, but the PCB traces, would limit that to say 30-50A. I've tested up to 20A, but I think 30A would be fine as well. Over that and we'd also have to change out the .005 ohm shunt used in the current measuring logic. So as is, I'd say the current limit is 0-30A.

-- Gary

 

[regmeister]

deleted

 

[SpeedEBikes]

chroot, not to be mean, but if you are asking such a basic question you probably shouldn't be using LiPo batteries. A basic mistake can easily damage or ruin the expensive batteries. A bad mistake can lead to a dangerous fire.

Anyway, there is practically no limit to how large a pack can be charged from a given wattage supply. It's mostly a question of your patience. However, charging too fast can degrade a pack or set it on fire.

Multiply your pack voltage by it's capacity in amp hours to get the watt hours of energy in a full charge. Divide that by the wattage of the charger to get a ball park figure in hours for a recharge.

How many lipo 6s pack can charged by meanwell's 350 watts. I cant find the formula math that calculate per watt on each 6s pack. I am planning charge 16 of the 6S pack in parallel (88v nominal 20Ah). I am not sure if 350 watt is enough for whole 16 at once charge.

Any cheap meanwell switching power supply. Mostly I see over 50 dollars on ebay. Which one is original meanwell due too many
clones chinese meanwell. I am looking for 24V DC 14.6A 350W Meanwell Switching Power Supply. Let me know

 

[GGoodrum]

Thanks Gary,

I was wondering if the battery medic Booster & the charge controller could be used at the same time? I mean, could the Booster, drive the charge controller from it's LED outputs?

Regards,
Richard

Yes, and no. Yes, the BM/Booster combo can be used at the same time as when you charge, but then you would need enough BM/Boosters for the whole pack. Doing it offline, you only need one.

The BM, and/or, the booster, can't replace the LVC/HVC boards, however, because they operate differently. The BM cycles the shunts, so there's a large hysteresias. the Charge Controller needs the HVC signal response to be instantaneous.

-- Gary

 

[mwkeefer]

Cellman... To replicate what your higher end / multiple profiles chargers are doing... Just setup a meanwell with 2 set voltages using 1% tolerance resistors instead of svr1... Use a dpdt center off to select between them and set position #1 for 90% of the max charge you want... Let this taper to /20 or better to nothing (on a properly modded meanwell the fan will cut out when current drawn falls to 0. Flip the switch and have It configured for your 100% charge state per cell and again let it taper and see what your final balance is like : )

-mike

 

[SpeedEBikes]

I like Mike's solution. Clean and simple. And easier to tune with accuracy for desired performance. Putting resistance inline with the output would require a low resistance high power resistor, I'd guess something less than 0.5 ohms capable of handling 5 to 10 watts dissipation. That will be a more expensive resistor and it will be awkward if you find a need to adjust to get a faster or slower taper.

Frequent balancing shouldn't be needed unless you have a problematic pack. In which case the burden of manually having to intervene for a two stage balance charge is not very onerous. I imagine it also wouldn't be too hard to modify Mike's approach with an automatic option that leverages off the existing shunt/current limiting arrangement to only select the higher voltage output when current is below a critical threshold.

Cellman... To replicate what your higher end / multiple profiles chargers are doing... Just setup a meanwell with 2 set voltages using 1% tolerance resistors instead of svr1... Use a dpdt center off to select between them and set position #1 for 90% of the max charge you want... Let this taper to /20 or better to nothing (on a properly modded meanwell the fan will cut out when current drawn falls to 0. Flip the switch and have It configured for your 100% charge state per cell and again let it taper and see what your final balance is like : )

-mike

 

[cell_man]

I'm not trying to say that using a PSU as a charger is bad and that a dedicated charger is so much superior and if my comments came across that way it wasn't my intention.

Anyway it was just a suggestion as to how you could get a unbalanced pack balanced with a high current charger and a low shunt current BMS. This would be equally applicable to a dedicated charger as even though they might reduce the current as it reaches the max charge voltage, it's not so significant.

 

[SpeedEBikes]

Another easy way to get a slow complete balance charge for a low balancing current BMS in a single shot with no intervention would be to do the R37 (or is it R33) mod to set a lower charge current. Ought to be able to set it up with an external switch to select between two charge rates. Or use a trim pot.

 

[mwkeefer]

Forget the trim pot except for gathering impedance references for the circuit part in the design / prototype phase, for long term and reasonably accurate current limiting across voltages with little or no noise, go with the dedicated resistors for various current levels and switch them in and out as needed...

One reason for a dedicated type MCU controlled charger (like an iCharger) to taper besides the CC/CV curve is the CP model, where max voltage (42v) and max current at CC/CV delta point if charging at 10A rate would be 420w which that iCharger can't do... it's rated as maximum output at 300w which would see your CV beginning current for a 10S 10A rate charge to 4.2v per cell or 42v for the pack as 300 / 42 = 7.14 A and then it would taper from there... Sometimes people are a bit misled by stats or specs... 10S10A should do 420w at end of CC phase and beginning of CV taper off? See what I mean?

Personally I do this with the meanwells now, I just run em with fan mods and in most cases (15S single unit chargers) I just clip a single shunt and 420w seems to be my CP factor so when I charge a 15S pack (assume nominal 55v at start of charge) I begin as high as 9.3 A (actually the shunt limits this a tad downwards of 8.5A) continuously tapering durring charge until hit the CC/CV transition at 62.42v I am pushing 6.73 A.

Cell_Man - If I had cells with your capacity, I would be looking for a way to charge at 10KW rates...

-Mike