Hey all...just bumping this thread as it seemed to be inline with what I'm looking for. Just finished assembling a 280ah Lifepo4 pack for our RV but a 120v charging solution is the next hump. I've seen a lot of discussion about server power supplies but there's so many rabbit holes when it comes to picking the best one (including the multiple threads linked here) that it gets overwhelming fast. Couple that with fuzz-brain right now from a concussion and I'm spinning my tires.
Can anyone share their outcomes with this path? Is there a "this is the one" PSU that ends up being the best choice at the end of the day?
I'm looking for something around 40-70 amps - I want to remain under 1000w AC draw so that I'm not maxing out a 15A circuit and leaving some overhead for other draws while the RV is plugged in.
Thanks for any insight.
Bit of a necro revive but here's the answer: So the whole purpose of looking at the server power supply route is $$$. You can get the 900W/1200W HP DPS units for $20 all day on eBay and I have been buying the 460W PD28 models for $8 each. For supplying one of the bigger lipo balance chargers (iCharger/Powerlab 6/Powerlab 8/etc) you can series two of the 1200W models and pretty much have all the power you'll need so long as the input amperage on your lipo balance charger is sufficient. There are some cases where 36V or 48V is necessary or beneficial to squeeze the full wattage of the charger out if you were maxing it out at its maximum number of cells in series. It is the case for nearly every "big boy" lipo balance charger that just supplying it ~12V is not sufficient due to input amperage restrictions that often leave you with the ability to only get 400-600W. Even if you are using an HP DPS 1200FB A on 240V it doesn't matter that the server power supply can output 100A...the charger will have its input restrictions.
You can buy a refurbished iCharger S6 off Progressive RC for $95. Add two of the 460W PD28's for a 24.5V input supply (38A max off the server PSU's) and you're in business for about $125 and you have a maximum of 40A of charging along with regenerative discharging and all the other cool features on the iChargers. *
Cons: due to the small size of the S6 running it beyond 30A is not something I'd advise. Even with an external fan trying to blow more air across the heatsink temps still get scary. But having the regenerative discharge feature, good balance current, plus much more makes this a no brainer if you are trying to charge medium sized (1kwh to 5kwh) NMC or LiFePO4 batteries...
Passive Balancing: due to the widespread use of active balance boards passive balancing has become a dinosaur. Not only is it terribly inefficient in so much as it has to drop all the high cells down to the lowest cell (which is a bitch when you have ONE cell much lower than the rest) but the amount of heat generated inside the chargers is compounds the issue I have with the S6. I would HIGHLY suggest NOT using the iCharger for actual balancing and instead use a $10 or $40 (3S/4S and 16S respectively to cover your standard 12V and 48V batteries). The only downside to using these for LiFePO4 is that balancing should not be started until cells hit 3.45V. For $50 you can get the NEEEY 4A Bluetooth Active Balancer and I believe this allows you to set a "balance start voltage" whereas with the simple PCB boards you can only add a switch that allows you to flip it on manually once you hit a certain point in the charging process. I'm sure someone out there could easily use that switch pad with a relay and an Arduino to monitor the cell voltages and switch the active balancer on at a set voltage. Obviously spending $50 on the Bluetooth model is going to be a simpler solution and since the actual balance current is derived from voltage delta you are rarely seeing more than an amp or two of balancing current so don't sweat the fact that it is "only" 4A.
NEEY 4A Active Balancer-Bluetooth with Balance Start Voltage
*Only works with 8S-24S. If using a 12V battery then just buy a regular $10 active balance board and add a switch to it and manually switch it on and off.
Refurbished iCharger S6-$94.99
I would also recommend the ToolKitRC 600W 20A M8P as a great iCharger Jr option. Only have had it for a week or two but at $37 plus tax shipped to your door on Aliexpress its quite the powerful charger and has the same balance start voltage (-100mV, -200mV, etc from terminal charge voltage) feature the iCharger has. My M8S was a decent charger that had some quirks but the M8P does not have the fluctuating current problem and the voltage calibration out of the box is quite good. Current calibration needs some adjustment but not terrible.
ToolKitRC M8P 600W 20A $37
Don't need a lipo balance charger? Ok there's no easy way to add an adjustable constant current feature to server power supplies that I've seen. The maker of the kWeld does make a PCB for a specific model of HP power supply that gives you voltage and current adjustment...but its like $90 or something similar...a bit expensive and of course you're then stuck with the lower voltage of ~12V. Not sure if you could series those PCB's on two PSU's.
So the answer is Aliexpress again. Quite a few modified HP DPS and Emerson PSU's that have a mysterious gray box on top with a voltmeter/ammeter. The most common models are:
2-15V 2-50A -can be found for $50 shipped
2-15V 2-60A -can be found for $80'ish shipped
2-15V 2-100A -can be found for $110 shipped
And then there are series connected versions of these for charging 24V batteries that only go down to 15V or something that prevents you from charging a 12V with that charger.
I have experience with the 50A Emerson model and as expected its fairly loud but it does work. Obviously NEVER run these for more than a couple minutes beyond 80% of their rating unless you want the magic smoke.
Modified Server PSU's For Single Cell and 12V Charging
There's also a new model out with a different screen that offers a bunch of features that could be very useful
3-15V 3-100A with Upgraded Screen for $100! Great Deal
Beyond this I would look at the modified ZXD2400 V4.3 telecom rectifiers. The simpler screen models are cheaper and can be $150 while the nice OLED one is usually $200.