Can I use an old Lab Power Supply to charge LiPo directly

[ryan]

Update... looks like my connections to the AC weren't as good as I thought. One of the input terminals was malformed and wouldn't accept a screw. I soldered the wire on, but ignored the bended tab part. Turns out it was loose and didn't connect right. Anyway, the unit turns on now.

BUT... I'm not able to get variable power.

Here are two videos to help debug. I appreciate all your help. Thanks.

1) This video shows the multimeter attached to terminals 8&9 in the back. These are the "output" terminals. If I turn the current dial above 6A it switches off current mode and floods the voltage to 132v. Below 6A the voltage is at zero.

[youtube]WsVHTKSYmtg[/youtube]

2) This video shows the multimeter attached to terminals 6&7. These are the "VOLTPROG" terminals and yield 4.16v consistently when the PSU is turned on. Above 6A this jumps up to 16.32v.

[youtube]8qwTtRPfgg8[/youtube]

I expected to turn all dials to zero (current to almost zero), flip the breaker to "on", and dial up the voltage to desired amount, view the results in the dashboard meters, connect multimeter to confirm, and charge charge charge. What am I missing?

 

[ZOMGVTEK]

It looks like they were using the volt program option on this supply. You need to remove those wires coming off it, and jumper 6 to 7.

Also, it looks like this unit is probably badly in need of a rough calibration. If you download the manual for this supply, you can follow the guide on how to calibrate it, so that the current mode isn't kicking in when the dial isn't at 0.

 

[ZOMGVTEK]

Also, be aware you can NOT turn the power supply off while the battery is connected. The result will be bad. A big diode across the outputs wouldn't be a bad idea if you plan to use this as a charger alone.

Can you break this down for me? What happens if the power goes out while I'm charging? PSU is turned off, but battery is near 74.7v. What happens, and what do I do to prevent negative or disastrous results?

It's going to depend on how this supply reacts, its just generally a better idea to have the supply on when you connect a load to it. Also, sometimes these old Sorenson supplies have a touchy OVP that wants to drop an SCR across the output. This would mean shorting your battery through the power supply, and it would be a bad thing. The best way to have no issues at all, is to run a diode on the output, like Sorenson recommends for charging batteries. Unfortunately it will add a bit of complexity to the charger, but then you shouldn't be able to do anything bad. You're probably going to want a big stud mounted one, and it will need a little heat sink. Another option would be to simply use a fuse on the output, that should be OK as long as the supply isn't going to be acting up often.

 

[ryan]

Awesome! That was it! Thanks ZOM.



Here's the next problem... volts top out at 63v. The unit says 80v. Applying more or less current doesn't change anything, so long as it's set above 6A (otherwise voltage is at zero).

At first I thought it was my jumper (I was using a tiny aligator clip test wire), but even replacing with a super short 8awg wire jumper only brought it from 61 to 63v.

It looks like they were using the volt program option on this supply. You need to remove those wires coming off it, and jumper 6 to 7.

Also, it looks like this unit is probably badly in need of a rough calibration. If you download the manual for this supply, you can follow the guide on how to calibrate it, so that the current mode isn't kicking in when the dial isn't at 0.

 

[ZOMGVTEK]

My guess would be that they adjusted these units very oddly so they would never go above 63V, or 14A or so. Thats why below 6A does nothing, and why it won't go above 63V. It's probably been 'calibrated' to be way out of calibration.

It's not hard to fix that, you basically need a accurate volt meter for most every adjustment IIRC. Just find the manual for your series and find out how to make it like the factory sets it. For a full calibration, you might need a 7.5 Ohm precision resistor, and a dummy load. But you should be OK with just the rough voltmeter stuff. Just watch out for OVP kicking in. They might have set that fairly low. You'd know when you hear a thud and the voltage slams to 0. It should be fine if you just crank the OVP as high as it will go.

 

[amberwolf]

If it drops in voltage below a certain current (but above 0A) then that means there is already a load on the there pulling that amount of current. So when you limit it to below that current being drawn, it dips in voltage in response. It's kind of a nice way to see how much max current something draws, in some cases.


Is that 63V with a load on it or with nothing but your meter on the output terminals?

If it's with a battery load, then that would mean the battery is discharged to 63V.

If it's with no load, then something else is drawing it down.


If it's no load, then there is a calibration routine on that same page I noted above. You dont' need the precision resistor and stuff to do a basic calibration, just to see if it'll go all the way up in voltage. But if you want it's readouts and voltages to match what's expected perfectly, then you'll need to do it just like it says on it's pages.


FWIW, if the output voltage went too high during testing, it is possible that the current limit circuitry is damaged, and thus causing problems with voltage output. It refers to some of that in that same section of the manual. Hopefully nothing has happened, as these things are pretty tough, but if it did it's still fixable.

BTW, here's a reference pic modified from one of yours (even though you already got the problem fixed) that you can keep around for later, if you need it. Before I saw Zomgvtek's post a little further down from your pics, I made it to post for you. The red is the shorting bars already in place that need to be, and the green is the one you needed to add (whch you have already done now).

 

[ryan]

Yay! I got 80.0v! More later. The doc AW linked to had the calibration steps. Everything checked out except for the max voltage (obviously). A turn of a potentiometer and I was dialed in pretty quick!

Thanks AW and ZOM!

 

[ryan]

This is why I love ES. Where else could a EE neophyte be walked through something like this.

AW, your diagram was right on. Exactly what I ended up doing.

I'm preparing the charging output leads now. If I plan to charge at 74.7v 18A, do I need to use the giant 50A Andersons? Or can I use the smaller 45A Andersons? (the smaller housing, but 45A contacts). I have a tight space, so I'd rather not spend it on a big Anderson connection if I can help it.

Also, should I install a diode in the charge line in case the power goes out during charging? Recommendation?

 

[ZOMGVTEK]

It's more likely than not that the supply will be fine if you switch it off while charging. It's still recommended to have a diode on the output, but not absolutely required. If you have a 20-30A fuse laying around, you can use that until you get a diode on the output. At least the fuse will blow, in the event of the OVP triggering and shorting the output.

There is still a few instances where its a good idea to have a diode on the output when charging a big battery. A 20-50A fuse on the output should do the trick, but a diode is best.

45A PP's will be perfectly fine. They should be cool to the touch at <20A. 35-40A and they start to warm up.

 

[amberwolf]

I second Zomgvtek's answers.

If you need a big diode, for cheap or free, they are common in these large PSUs, and in server and networking PSUs. You may be able to find a dead one that is being tossed out that you can then salvage the diodes from (because they're probably still good).

I probably have some around here, too, but they are unlikely to be rated at 80V+. Or for the ones that are, not at 18A+. But I'll keep an eye out.

 

[ZOMGVTEK]

Big diodes are fairly cheap, and you can often pick them up for next to nothing if you look around.

I would swing for a 50A+ stud mount, and it will need to be mounted to some sort of small heat sink. Nothing very hard, just buy or find a random smallish chunk of metal, drill a hole in it, and bolt the diode in. If you're crafty, you can probably find a way to mount it right to the supply. You should be able to put the sense lead past the diode so it adjusts for the diodes fluctuating drop as the current changes.

Something like this will do.

http://www.ebay.com/itm/Wind-Hydro-Solar-Blocking-Diode-600-Volt-40-Amp-Stud-Mounted-Diode-Anode-S-/280817024246?pt=LH_DefaultDomain_0&hash=item4161ffbcf6#ht_952wt_1180

This ones all shiny and new. They're not worth a lot, so its going to be hard to find someone selling ancient dusty ones cheap. Anything that looks substantial should do. Just don't go for a billion of those little black ones.

 

[amberwolf]

Just remember that teh diode body on those stud diodes is usually electrically connected to one terminal of it. So you have to make sure whatever you bolt it to is electrically isolated from teh case, or the case will be live with the voltage you set (or battery voltage).