Switch mode supply mod

[Jeremy Harris]

I took a gamble and purchased one of these: http://cgi.ebay.com/350W-48V-7-2A-Switching-Power-Supply-CCTV-Radio_W0QQitemZ310040654028QQihZ021QQcategoryZ48632QQssPageNameZWDVWQQrdZ1QQcmdZViewItem to see if I could mod it to run at about 60V. The idea is to use it as an on-board charger for my motorcycle build, which is using a 48V, 40Ah Headway LiFePO4 pack.

Today I took the PSU apart and spent a couple of hours reverse engineering it. I believe that these supplies are available from several different suppliers, all with essentially the same design, usually with a number like "S-350-48". The supply is based around the TL494 PWM chip (see here http://focus.ti.com/lit/ds/symlink/tl494.pdf for details). It's easy enough to up the voltage range, by simply adding a 15k resistor across the 3k9 resistor adjacent to the voltage trim pot. The snag is that the over-voltage protection circuit kicks in at about 53 volts, so seriously limiting the ability to trim the output up.

The fix for this is easy. Underneath the main ferrite transformer there is a 53V zener diode, labelled ZD1. Simply unsolder one end of this and add a 10V zener in series. This ups the over-voltage protection to 63V, which is the same as the rating of the main output filter caps.

The supply is good for over 6 amps (as high as I've tested it) at 60V, with no problems. I reckon it will make a neat on-board charger. All I need to get on and build is a shunt regulator type charge management system, like the excellent one from Gary/Bob. I've already got one of Gary's LVC cut-off boards, to switch off the controller in the event of a cell going low.

I love it when a plan comes together...................

Jeremy

[PJD]

Agreed - they will make a good compact-sized companion to a Bob Mcree BMS - if he can ever get the thing out. I assume with a change to 100V output filter capacitors it can be turned up higher? What are the output rectifiers good for?

[Doctorbass]

Welcome in thee DC or dc-dc power supply world of mods!

That's great to see that you've been able to mod this common model found on ebay!

I wonder if you border with the input switching transistor that may have been calculated for the rated power of 360W... maybe the output diodes can handle the same current and a bit higher voltage but i would be not sure about the input transistors that will need to handle more current by rising the output power by the voltage increase...

I would suggest to add some fan and additional heat sink... and for the cap that have the same rating than the output.. that give you no safety margin... change those for 80V or 100V

let us know in long term if it still work !

Doc

[Jeremy Harris]

Hi Doc,

These supplies already have a temperature controlled fan, and use the alloy case as the main heatsink for the input power transistors and the dual fast-recovery output diodes.

The one I have is rated at 350W, which is about 7.3A at 48V. I'm including current limiting in the charger circuit that will initially charge at 6A maximum, dropping to 1A for the balancing phase. I reckon this should be OK, as it's only slightly over the original 350W rating.

The input stage power transistors are a pair of 2SC3320's. These are rated at 400V Vceo, 15A Ic, 80W. I would guess that switching losses at the front end might be the major limiting factor, so assuming these are around 20% maximum (probably pessimistic) then at the rated 350W the front end power transistors will be dissipating about 35W each. I reckon they will take a bit more without too much trouble.

The output diodes are a D92-02 pair, rated at 20A, 200V, so this should be OK. Looking around the board I think that by changing the three 1000uF, 63V output caps the supply should be good for a higher voltage, if anyone needed it. I'd be inclined to connect a couple of 48V supplies in series if I wanted 100V though, as they can be adjusted up to 52V as standard. Looking at the design, I can't see any obvious problem in running them in series, plus these supplies are very small and light for the power (and cheap).

Jeremy

[manfred59]

I have bought a 48V 10.4A 500W Switching Power Supply from HK for charging my 15s6p battery. It seems to be different to the 350W one of Jeremy!
1. It should have an+ / - 10% adjustable output. But I can only adjust between 46,5V and 48,4V?
There are on both front sides trim pots - see the foto. What does the right one do? - should it increase the voltage to 50,8V?
2. Has anybody moded this Power Supply to a higher voltage like 55V. Would it be the same way like Jeremy did? But near the left trim pot there is no resistor with 3k9 or so!
The Z1 looks like two zeners in serie?

[Jozzer]

Hi there, I have some of these too, there is another pot to be found somewhere in the middle of the supply taht trims coarsde voltage, the pot at the end only does fine adjustments...

[manfred59]

Indeed, the pot in the middle can adjust the voltage to max. 50,6V.
But how can I get 55V, has this anybody tried?
manfred59

[Jeremy Harris]

I can't offer a fix for the 500W supply you have, but can confirm that it looks quite different internally to the 350W supply I modified.

I've looked at three of the 350W supplies now, all from different suppliers, and all have been the same internally and all have had similar markings on the circuit board. My guess is that the 500W ones are radically different for some reason.

Jeremy

[disadvantage]

Today I bought one of these 48V 500W power supplies from eBay.

I don't know how long it'll take to get here (Iowa USA) from Hong Kong, but when it does I'll have a go at figuring out how to raise the output voltage.

Thanks for making us aware of this bargain, Jeremy.

[disadvantage]

I got my power supply today; airmail from Hong Kong.

I'll hook it up and start testing when I get home from work.

[disadvantage]

I got the power supply hooked up and running. It appears to work correctly.

The model number is GM500-1L, 48V 500W. There is a web site on the label: http://www.guolilai.com

I tried searching the web site for PDF documentation on the power supply, but I couldn't find any. Google also turned up nothing.

I'd like to read about what the VR1, VR2, and VR3 potentiometers do, and what rating are the FS1 and FS2 fuses.

I emailed the eBay seller for some PDF documentation. Hopefully, dangling some positive feedback as a carrot will get the seller to help me.

In any case, tonight I experiment more, and try tracing the output circuitry.

[monster]

did anyone get anywhere with these PSU mods? give us an update.

[disadvantage]

did anyone get anywhere with these PSU mods? give us an update.

I got my power supply pulled out of its case, and put heatsinks on the output transistors and diodes.

I still haven't figured out what VR2 does, but VR1 is definitely a fine voltage adjustment, and VR3 is a coarse.

Z1 is two series connected zener diodes on my power supply also.

I identified 3 surface-mount resistors on the bottom of the board that probably affect the voltage adjustment. R1 is labeled 5102 = 51K, R2 is 1001 = 1K, and R4 is 2701 = 2K7 (2700 ohms). These must be 1% precision resistors, as there are 3 significant digits for their values.

I'm taking some vacation time off next week, so I'll have more time to fuss with this project.

[fechter]

VR2 might be a current limit adjustment.

[AndyH]

I got the power supply hooked up and running. It appears to work correctly.
The model number is GM500-1L, 48V 500W. There is a web site on the label: http://www.guolilai.com
I tried searching the web site for PDF documentation on the power supply, but I couldn't find any. Google also turned up nothing.

No docs but did find basic specs. http://www.guolilai.com/English/001/guo74.htm

Andy

[bquick]

Jeremy,

How are you planning on controlling the current? Can you hook one of these directly to a battery pack?

I'm wondering if I would be better off with a CCCV charger instead. I can get a 24V, 5A model from the Hong Kong ebay company. If I put 3 of these in series, I can do 72V at 5A, for an 8 hour charge on my 40aH pack.

- Brad

[disadvantage]

Tonight I temporarily modified my GuaLiLai switching power supply, and got it to output over 67 volts. I was afraid to go higher during my tests, for several reasons.

The output capacitors C3, C4, & C5 are only 50V, so at 67V I was well above their maximum. I quickly made my tests and took my pictures. I don't have any high voltage, high capacitance replacements on hand.

DigiKey has 63V, 80V, and 100V electrolytic capacitors. I need nearly 64V to charge 15S eMoli cells, so I will need at least 80V capacitors. Electrolytic capacitor voltages are often chosen 50% over the expected voltage. 100V parts would be better, but I am unsure if they would fit inside the aluminum box. Maybe I can lower the capacitance to get capacitors that will fit; the originals are 2200uF but 1800uF and 1500uF are available at 100V. I don't need lots of output filtering for charging batteries, though the switcher's feedback circuit might complain if I go too low.

Also, I could smell something burning; carefully touching a wet cotton swab on various parts indicated R3 was hot enough to evaporate water. R3 loads the power supply when there is no output connected. This metal-oxide resistor is larger than the 1W size from Radio Shack; the body is about 15mm long which matches a 2W resistor. 48V^2 /1K5 = 1.5W is within range; 64V^2 / 1K5 = 2.7W is not.

ZD1 is a pair of series connected zener diodes. If you look at the board from the traces side, ZD1 straddles surface-mount R6. With the diodes pulled from the circuit board, I connected a 18K resistor in series with each, one at a time, with a 36V power supply, anode to negative and cathode to positive. The resistor was to limit the current to the milliamp range, so the zeners wouldn't blow up. I measured 27V across each one, so in series they provide a 54V zener voltage.

This would explain why people had trouble adjusting the voltage above 55V. 55V^2 / 1K5 = 2W, equal to R3's power rating.

DigiKey has 51, 56, 58, 60, 62, 68V, and 75V zener diodes. I will probably chose a single 68V since I don't want to connect several diodes in series. To get the odd-ball 54V, the designers had to use 2 series zener diodes. For my brief tests, I added a 12V zener diode to the string, for a total of 27 + 27 + 12 = 66V.

I noticed that above 67V, the burning-resistor voltage, that the fan would come on even though the power diodes and transistors were cold. I can't explain this, but it might not affect me since I don't need that much voltage.

Finally, I replaced R4, the 2701 surface mount resistor on the bottom of the board. I tack-soldered a 1K8 resistor in place of the 2K7. This change, along with adding a zener to the ZD1 string, is the one that allowed the power supply to output more volts -- but only for moments because it was unsafe!

VR3, the coarse voltage adjustment, is connected as a rheostat; the wiper and one end are shorted on the board. The other end is in series with R4, the 2701 fixed resistor.

Before making changes, I turned the brass screw on VR3 until the output voltage was as high as it would go. Then I desoldered and measured VR3, its overall resistance was 500 ohms. I also measured the resistance across the non-shorted terminals; it was a short circuit. This meant I needed to lower the series combination of R4 and VR3 to raise the output. This matches my experience with another switcher I've modified.

I chose 1K8 because I wanted to raise the voltage by at least 1.33 or 33%. 2K7 x 48V/64V ~ 2K ohms; but 1K8 would allow me to go a bit higher; about 50% = 48V x 2K7/1K8 = 72V. This extra range allows me to trim above and below the 64V spot that I want.

So -- to make this change correctly so it is safe, I need to:

1. Replace C3, C4, and C5 with higher voltage electrolytic capacitors. 80V is minimum, 100V would be better. I could lower the capacitance from 2200 uF to help fit the replacements in the case. 1800uF and 1500uF are available.

2. Replace R3 with both a higher value and higher wattage resistor. Resistance will be 2K = 1K5 x 64V/48V. Wattage will be 3W; 72V^2 / 2K = 2.6W which is within range.

3. Replace the ZD1 zener diode pair. I will choose a 68V zener to avoid multiple diodes and keep the supply neat looking. I will use a 1W size, even though it is larger than the original two, because they are cheaper and a larger diode won't hurt anything.

4. Replace R4; 2K7 (2700 ohms) becomes 1K8 (1800 ohms). For my tests I used a 1/4W resistor because that's what I happened to have. A 1/10W resistor radial-lead resistor would fit better; or I could scavenge a surface-mount resistor from some discarded electronics I have in my junk box. Power rating isn't critical here since the resistor is in the feedback circuitry which is low-power.

Have I missed anything? Helpful comments would be appreciated.

GuoLiLai002.jpg

GuaLiLai PS modded for 15S eMoli cells ~63.75V

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The temporary changes I made, please read my post for details.

GuoLiLai005.jpg (49.52 KiB) Viewed 3268 times

[disadvantage]

I checked my Hotmail, and I have parts from Mouser.com arriving Tuesday to complete this mod correctly.

In the mean time, I can work on another important project of mine.

[disadvantage]

Mouser.com order arrived today, so I started making power supply changes.

The zener went in easily, and so did the power resistor. But I ran into trouble replacing the electrolytic capacitors. The new ones are just too big!

Originals are 18mm dia x 26mm hgt. My replacements are 26x30.

At mouser.com I found some 1000uF 100V capacitors that are 22x30 and 18x40. The 22x30 ones are bigger diameter but their height is good. The 18x40 ones are the same diameter but they may be too tall to fit in the case.

I'l order a set of three of each size, but not too soon. I'm working on another project that might need new parts as well, and I'd like to combine orders to save on shipping.

GuoLiLai009f.jpg

Capacitor Woes

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[flip_normal]

Nice work disadvantage!
That's the 500W 48V GuaLiLai you've got there isn't it?
'Cos the one's I've got look slightly different on the PCB traces around where you did the temporary mod. R4 on your's 'aint there on mine??

500W 48V GuaLiLai PSU traces

500W 48V GuaLiLai top.jpg

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Is there any way to tell from these pics if this will work on this board?

Cheers.

[disadvantage]

Yes, I have the 500W 48V model of the power supply. The pictures you posted look identical to mine.

R3 is a big fat power resistor on the top of the board, right next to the power out screw terminals.

R4 is a tiny surface mount resistor, on the *bottom* side of the board. I tack-soldered a 1/4W replacement, right next to my zener string replacement, on the bottom side.

You mention you don't have R4; did you check the bottom side? Or maybe you have a jumper wire? Is there a spot marked R4 on the bottom side of the circuit board? There's no R4 marking on the top side.

[flip_normal]

disadvantage, thanks for the reply, I think I've got it. There are some small differences in the boards.
Here's what I got.

GuaLiLai 500W48V detail.jpg

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R3 (1K5) on yours is R4 (2K) on mine.

R4 (2K7) on yours is R5 (2K7) on mine, I think.

I'll give it a go when I get the components.

One other thing. I've got one of these PSUs which trips the RCD in the fuse box when I plug it in, anyone got any ideas how I could work out what's wrong with it and how to fix?

Cheers.

[disadvantage]

I owe you an apology, flip_normal. I assumed all GuoLiLai 500W 48V power supplies have the same circuit board layout. My last post was based on this.

I was at work, away from my PS, when I last replied. I went home and took a closer look, and your PS definitely looks different, even though the topside components appear to be laid out similarly.

This morning before leaving for work, when I had good daylight, I took some closeup pictures. Today I played Hookey a bit, and labeled them like you did yours.

Topside with components; mine is labeled M1B-003, yours is M1A-002. I wonder if there is a difference beside the layout of the copper traces?

GuoLiLai026f.jpg

Topside with Components, Annotated

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Bottomside with wires carrying mains power from one corner of the board to the other. You mentioned one of your PSs blows a circuit breaker when powered up; I would first carefully check these wires and their solder joints -- or better yet, just replace them outright like I did. If those are okay, then it might be other solder joints, or the input PFC (power factor correction) inductor (looks like a transformer), or input capacitors or MOVs might be shorted. The short would have to be big & obvious to blow circuit breakers.

GuoLiLai029f.jpg

Bottomside with Mains Lines, Annotated

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I think you figured out how to boost the output voltage on your particular model of switcher PS. Looking at your pics and following your description of changes, they look & sound correct. Be sure to check for a zener diode which limits the maximum voltage, the voltage rating on the output capacitors, and the power rating of the output bleeder resistor. Make your changes safely, so you don't burn down your house.

Here's what the sticker on the side of my PS looks like; Is yours the same?

Sticker on Side of Power Supply

GuoLiLai033.jpg (24.87 KiB) Viewed 3024 times

When my PS is back together again, I can play with VR2, which Fechter thinks limits the maximum output current. I think he is correct, but I am unable to verify right now.

[flip_normal]

Disadvantage: no apology needed, your the one sharing all the know-how. Many thanks BTW.
I haven't made any changes to mine yet, it was somewhat misleading when I said “I think I've got it ”. R4 on mine is 2K stock.

There aren't any wires going across the underside of my PSUs, and yes the mfr sticker is the same.

Thanks for the trouble-shooting tips, I can't see any signs of burnt components or scotching on the faulty board but I'll check it some more as per your advice.

Cheers.

[manfred59]

So , I have done the mod of the 500W M1A-002 PSU like the one which flip_normal has.
Due to my A123 pack 15s6p I replaced the zener with a 56V/1W one and changed the capacitors like Disadvantage did. I also changed R5 (2k7) with 2k2 resistor.
R4 (2K) I did not change.
I have got it to output to 50,2 - 61,3 volts, but after plugging into 230V no battery connected the voltage shows about 5 seconds the max. voltage (56V) and then the voltage decreases quickly to 0V
Perhaps has Disadvantage an idea why this happens.
ciao, manfred59