diy solar

diy solar

AC based charging using server power supplies

DThames

Solar Wizard
Joined
Nov 22, 2019
Messages
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I have been tinkering with an emergency battery/inverter system and part of the plan is to be able to charge from a generator if there is not much sunshine. If I could get enough charge in the battery to carry critical loads overnight, that would be great. I have a 24v battery and found you can connect 12v computer server power supplies in series. I purchased two HP supplies, each rated for 850watts at 120v or 1000watts at 240v. There is a modification that can be done so the 12 max limit is removed and with resistors or a pot, you can adjust the output. They will still regulate to the set voltage, but it is now not locked down to 12.3v or whatever. With a 1k pot the range is about 14v-19v. The internal boards are connected to chassis ground and the ground wire from the power cord is also connected to chassis ground. While others had worked to insulate the board from the chassis, metal standoffs and through hole plating on the board made this look like a less than ideal solution for me. So I decided to float the entire mess and put it in an insulted enclosure.

I got some sticky pad standoffs and mounted the boards to some resin impregnated material (sample material junk from work). XT60 connectors were soldered to the connection blades. I 3D printed an end cap that would hold the fans. I then printed some pieces that can be used as extensions like the leaf in the dining room table. The voltage adjustment pots are mounted in the first leaf. Only the end cap was glued in place at the time of the photos but I wanted to do a test run before gluing the cover together and to the board.....so the rubber bands :) I set the output to 30v, connected to my X8 Icharger, and set the charge current at 25amps.

I also connected my laptop power supply based charger to add another 8 amps.

500watts of solar is doing about 0.5 amps today, so a good day to test AC based charging.
 

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VERY NICE!

The only concern I have about those is when you have parallel supplies like that, one of them always has a substantially larger portion of the load due to slight voltage disparities between them. Even if set to the exact same voltage, there's always a difference.

Regardless, you can push 2X than you can with 1X, so it's still a win-win.

What supply is that? I could use something like that.

Is the 1K POT restricted to 14-19V, or can you adjust down in the 12.3-14V range?
 
They are in series to get the voltage up over 24v. My plan is to be able to bulk charge with them and a power resistor. You can get over 60 amps @12v out of them on 120v AC, way more than that X8 charger can manage. I have considered connecting them to my 40amp Tracer and let it go into current limit mode but I don't want to risk its little life.

The model is HP DPS800GB. I think maybe 2 or 3 Kohms might let you get it down to 12v. After I put the pot on there and saw it was 14v, I added a 220 ohm in series to the pot but it didn't bring it down much. Again, you have to do a little surgery to open it up for adjustment.....cutting a pin off of a chip.
 
Oh... duh. I can see that now from the output. Sorry about that.

Nice 3D print work. I love having that ability to just make a shape that quickly gets something done. My wife is always having me whip something out that does something she needs for work.

Thanks!
 
Oh... duh. I can see that now from the output. Sorry about that.

Nice 3D print work. I love having that ability to just make a shape that quickly gets something done. My wife is always having me whip something out that does something she needs for work.

Thanks!
About a year ago I told my wife that one of my co-workers that she knows got a 3D printer. "That would be cool", she said. We had one right away :)
 
Oh yes. My wife has not realized that she was giving consent for purchase with a statement like that many times... :)

We have TWO 3D printers now from a similar exchange...
 
One more image, I got the AC end closed up.
 

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I have been tinkering with an emergency battery/inverter system and part of the plan is to be able to charge from a generator if there is not much sunshine. If I could get enough charge in the battery to carry critical loads overnight, that would be great. I have a 24v battery and found you can connect 12v computer server power supplies in series. I purchased two HP supplies, each rated for 850watts at 120v or 1000watts at 240v. There is a modification that can be done so the 12 max limit is removed and with resistors or a pot, you can adjust the output. They will still regulate to the set voltage, but it is now not locked down to 12.3v or whatever. With a 1k pot the range is about 14v-19v. The internal boards are connected to chassis ground and the ground wire from the power cord is also connected to chassis ground. While others had worked to insulate the board from the chassis, metal standoffs and through hole plating on the board made this look like a less than ideal solution for me. So I decided to float the entire mess and put it in an insulted enclosure.

I got some sticky pad standoffs and mounted the boards to some resin impregnated material (sample material junk from work). XT60 connectors were soldered to the connection blades. I 3D printed an end cap that would hold the fans. I then printed some pieces that can be used as extensions like the leaf in the dining room table. The voltage adjustment pots are mounted in the first leaf. Only the end cap was glued in place at the time of the photos but I wanted to do a test run before gluing the cover together and to the board.....so the rubber bands :) I set the output to 30v, connected to my X8 Icharger, and set the charge current at 25amps.

I also connected my laptop power supply based charger to add another 8 amps.

500watts of solar is doing about 0.5 amps today, so a good day to test AC based charging.
This is exactly what I have been looking for! Where did you find the mod, or did you invent it?

I really want to try this, and I need as much direct data as you are willing to give. The HP supplies are easy enough to get. Is there a Schematic on the mods you made? (praying fervently)

If you know of it, has anyone else here on the list done something like this? I love to gather as much data as possible before proceeding.

Thanks in advance for your time in replying.
 
DOH....:confused:

Just now watching the you tube you pinned. Great stuff and thanks for posting it!
 
This is exactly what I have been looking for! Where did you find the mod, or did you invent it?

I really want to try this, and I need as much direct data as you are willing to give. The HP supplies are easy enough to get. Is there a Schematic on the mods you made? (praying fervently)

If you know of it, has anyone else here on the list done something like this? I love to gather as much data as possible before proceeding.

Thanks in advance for your time in replying.

There’s a long and very helpful forum thread on this subject here. There are details in that thread of the pinout for a number of different server PSUs, so if you find a pair on eBay you can use the search thread function to see if someone has posted details of it. See also this thread and also this one for more details of suitable PSUs.... Reading that little lot will keep you busy, but there’s a lot of good reference info!

I did this many years ago and still use the 24V 1.3kW PSU which resulted from it. The OP in this thread is right to highlight that you should make sure the whole thing is enclosed in a well insulated case (I used polycarbonate plastic sheet cut to size and fixed with 3M VHB tape) to cover the whole outside.

For an extra layer of protection, consider adding a neon 120/240V AC rated indicator lamp wired between the two metal PSU cases. If either has a fault which causes the metal case to be live, the neon indicator will light.
 
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There’s a long and very helpful forum thread on this subject here. There are details in that thread of the pinout for a number of different server PSUs, so if you find a pair on eBay you can use the search thread function to see if someone has posted details of it. See also this thread and also this one for more details of suitable PSUs.... Reading that little lot will keep you busy, but there’s a lot of good reference info!

I did this many years ago and still use the 24V 1.3kW PSU which resulted from it. The OP in this thread is right to highlight that you should make sure the whole thing is enclosed in a well insulated case (I used polycarbonate plastic sheet cut to size and fixed with 3M VHB tape) to cover the whole outside.

For an extra layer of protection, consider adding a neon 120/240V AC rated indicator lamp wired between the two metal PSU cases. If either has a fault which causes the metal case to be live, the neon indicator will light.
Fantastic Info, Thank You! I will devour that information with glee!
 
OK next question is a voltage or amperage cut off. How is this done?

Can you just leave the charger on say 14.1 without worrying about it?

I am wracking my brain to figure out if I use a PSU without a charger circuit in it, can I just rely on a an AMP/Watt meter to tell me when to stop the charging?

HELP:unsure:
 
@george65,

Thank you! I have been looking for a simple answer like this for weeks.

My plan now, is to hack a server PSU to precisely deliver 14.1 V

making that part of my system, seems to be the last design element I was missing!

More once the cells arrive and I start the build. the PSUs are on order! Thank you once again.
 
@george65,

Thank you! I have been looking for a simple answer like this for weeks.

My plan now, is to hack a server PSU to precisely deliver 14.1 V

making that part of my system, seems to be the last design element I was missing!

More once the cells arrive and I start the build. the PSUs are on order! Thank you once again.
I think the unit will behave like a power source, not like a charger. In other words, it will bust a gut trying to supply the set output voltage. There needs to be a current limit of some sort. A 50 watt, 0.1 ohm resistor would give you a current limit of about 21 amps if the battery was 12.0v and the power supply was 14.1v.

I had the supply sitting by me one morning last week and I looked at anew and thought, "Where are the exit air holes?" I had been so interested in closing it in and mount the AC sockets that I just forgot air exit holes. So I pulled the end off (had used super glue on the sockets and made a new end for it.
 

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OK so why a current limit? It will be limited by it's output capability, about 63 Amps. Since my Battery will be 280 AH, why is it necessary to limit it?

So I take it you ripped off the tape? :unsure:

Surprised it didn't overheat!
 
This is something I’ve an interest in but know little about although I’m fairly capable of building it Even if I have little knowledge. The video explained it fairly well and off the back of it I’ve bought the psu. What’s the worst that can happen? That probably doesn’t need answered!!!
By my maths at 240v(uk)I will get about 70.1a output max.
since it’s auto ranging it should happily run from my inverter generator without cutout issue, if the revs/voltage drops it may just return lower power. According to my understanding anyways.
how do I attach the output terminals? Just solder to the board or can I drill and a fix terminals? Thinking that may cause damage?
I will be building a plastic box for it to sit in similar to the 3D printed one above but I’m thinking cut and glued acrylic.
 
OK so why a current limit? It will be limited by it's output capability, about 63 Amps. Since my Battery will be 280 AH, why is it necessary to limit it?

So I take it you ripped off the tape? :unsure:

Surprised it didn't overheat!
I’m also confused by this. As far as I’m aware when the battery cells reach 14.1v the power draw should taper off.
 
I have seen them drilled and terminaled. I have also seen them soldered.

I think your correct on all counts, but like you I am a newb to the finer aspects.

With a load on it, I don't see how there could be runaway amperage. Since the voltage will be fixed, and my load can take all the unit will push, I think this works.

Anyone out there say this is wrong? If so please correct me and tell me how to get the most from the power supply. ?
 
If charging at 14.1v thru a psu, on a 280ah cell in my case a 560ah bank @12v. As long as I keep an eye on the capacity meter thingy and check the bms app, I can’t see how it can go wrong. Failing that if there is a runaway the bms should kick in and shut it down.
I won’t be leaving mine unattended and running it from a genny. At the 70a max I can get out of a psu &14.1v it’s only 0.25C. The cells are rated at 0.5C charging rate.
@Mark44, what’s a retired traveller in the USA? I’m guessing your not a New Age traveller like we have in the uk? Kinda like what I am. Or do you mean traveller as in gypsy? That’s my heritage, in descend from Scottish travellers(gypsys) from that I can not retire and have no wish to.
min not having a dig in anyway, just really curious of the meaning of traveller across the world
 
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