The volts peaking at 12.7v no matter what resistor I’ve tried is what makes me think it’s a different chip and possibly different functions for the legs. This is probably a good time to point out I know nothing about electronics and I’m just following the video
AC based charging using server power supplies
- Thread starter DThames
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Getting >12.7-12.8 is harder since you have to bypass overprotection circuits. For some this can be found online, but not all supplies use the same electronics for this.
But it's not always needed to get >13V.
Many powersupplies don't have CC mode, but shutdown on overload. So for using it as a charger isn't advised anyway.
If you want to feed a MPPT (instead of PV) the MPPT will take care of the CC mode and charging parameters. But in those cases, there is always an addtional drop, so the PV input generally must be a few V above the battery voltage. Using a single supply would require to bump it to 16+V or more, but not all have eg output capacitors which can handle that.
Way easier to wire 2 in series to a 24V input, and let the MPPT handle the charge of the 12V battery. In that case, you don't have to mess with adjusting. Only rewire it to get it running, and make it floating from GND since you have to serie-wire 2 of them.
But it's not always needed to get >13V.
Many powersupplies don't have CC mode, but shutdown on overload. So for using it as a charger isn't advised anyway.
If you want to feed a MPPT (instead of PV) the MPPT will take care of the CC mode and charging parameters. But in those cases, there is always an addtional drop, so the PV input generally must be a few V above the battery voltage. Using a single supply would require to bump it to 16+V or more, but not all have eg output capacitors which can handle that.
Way easier to wire 2 in series to a 24V input, and let the MPPT handle the charge of the 12V battery. In that case, you don't have to mess with adjusting. Only rewire it to get it running, and make it floating from GND since you have to serie-wire 2 of them.
My plan was to use it as a charger running from a generator, I was trying to get it up to 14.0/14.1v output. It would never be used when I’m not sitting next to it and would be well below the bms settings.
this is the video showing it going up to around 16v and saying it can handle it but that’s about it’s limit.
this is the video showing it going up to around 16v and saying it can handle it but that’s about it’s limit.
Sverige
A Brit in Sweden
The suggestion of a neon indicator wired between the metal cases of the two PSUs is to cover the eventuality of one of the cases becoming live through an internal fault, mitigating the danger which arises from the fact that the earth connection to the case of the second PSU must be broken to avoid short circuiting the output of the first PSU (since case is joined to 0V output line, and 0V of PSU2 is connected to 12V of PSU1).
If both PSU cases simultaneously become live, then the earth connection to the case of PSU1 has failed at the same time that both PSUs somehow developed a fault causing their metal case to become live. With luck this bad, the only thing to do is to throw it in a skip and go down the pub for the rest of the day....
DerpsyDoodler
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And if both become live, what happens? A bit of explosive neon light? This is what I was getting at. I would rather not introduce another hazard under the guise of safety. If the light can handle this state, then great. Otherwise...nope nope nope...
Sverige
A Brit in Sweden
If both PSUs are plugged into the same AC phase then with both cases live there’s zero voltage difference between them and the indicator remains unlit. You’re not introducing any hazard by adding a neon indicator, but you are protecting against a hazard which lifting the ground connection on PSU2 introduces.
DerpsyDoodler
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Thank you. That’s the itch (concern) I was looking to scratch.
I just want to mention that server power supplys are not current limited and will go into hiccup overload protection if the connected load draws too many amps, meaning the psu shuts down and only restarts if the "fault" (in our case the load) gets disconnected.
That is true. Some sort of current limit like resistor or light bulb is needed. I put some 10 turn pots on mine so I can adjust the voltage output precisely. I can crank up the output voltage (while connected to the battery) and with an amp meter, adjust the volts to get the amps to a reasonable range. Then come back later and adjust as needed. It is not an ideal solution but is good for the emergency supply box.
I am building an agm charging system using a 480W 48V meanwell power supply (that has constant current so no resistor etc needed) but I will add a simple arduino or esp driven pwm mosfet to limit the power going into the batterys (higher pwm signal, more on time, more current, in my test setup I was able to controll down to a couple millivolts and nanoamps per step) (My system will be designed so all available energy thats not used in the house from an inverter will be pumped into the batteries)
PrivatePIlot
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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.
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.
Hi, I've done a lot of DIY UPS etc in the meantime, what battery voltage do you have? I found a couple very good MeanWell power supplies that feature constant current limiting (very good for charging ups batterys). But for a 280Ah LiFePo4 bank I would really really recommend getting a suitable LiFePo4 charger to keep the battery healthy.
PrivatePIlot
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Sorry, should have mentioned, it has a high end BMS, so I just need a supply.
It's a 4s pack.
It's a 4s pack.
Meanwell PB-1200-12? That is a 60A charger.
you do need a charger, since that does go into float once the batteries are full. A power supply doesn't. You can use a PSU to charge, but need to manually stop charging.
What do you call a high end BMS? I haven't seen BMSses which are actually chargers and thus lowering voltage. A BMS is the last line of defense, and does cutoff if the thresholds are reached, but it's not intended to act as a charger or whatever.
Also, keep in mind most powersupplies are 12V, and can't be adjusted to 14V. You want like 14V in order for the balancer to work as well. Charging with 12V isn't going to do much
Server PSU's generally can be modified to output higher voltages, but 14V+ is requiring to disable/modifiy the OVP as well.
Also, I'm not fully sure if they have CC so actually CAN be used as a charger.
Better get a 15V powersupply and dail it down, it's more easy to get 14-14.2V than 'upgrading' from a 12V.
you do need a charger, since that does go into float once the batteries are full. A power supply doesn't. You can use a PSU to charge, but need to manually stop charging.
What do you call a high end BMS? I haven't seen BMSses which are actually chargers and thus lowering voltage. A BMS is the last line of defense, and does cutoff if the thresholds are reached, but it's not intended to act as a charger or whatever.
Also, keep in mind most powersupplies are 12V, and can't be adjusted to 14V. You want like 14V in order for the balancer to work as well. Charging with 12V isn't going to do much
Server PSU's generally can be modified to output higher voltages, but 14V+ is requiring to disable/modifiy the OVP as well.
Also, I'm not fully sure if they have CC so actually CAN be used as a charger.
Better get a 15V powersupply and dail it down, it's more easy to get 14-14.2V than 'upgrading' from a 12V.
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PrivatePIlot
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So, my understanding (and based on how many others who use PSU's for charging, including lots here) is that you set the BMS accordingly to disconnect once the SOC you desire is reached. So in my case, being a bit conservative, I'd set the BMS to disconnect charging at 3.35v (90% SOC) and not reconnect again until 3.25V, 80% SOC, or a bit higher if I wanted the PSU to maintain a tighter window. I ultimately don't care if the PSU stays on constantly inside the 90% to 80% SOC window but isn't in active use.
Am I incorrect in my understanding that this will work just fine? Because it seems to be exactly what most people are doing.
Lots can, which is the discussion in this thread. From a response I received on another forum it looks like the DPS800-GB (HP) is a popular unit that can be cranked well past what is needed for LifePo4 charging.
The PB series only has a 1000W model,b the NPB has the 1200W. But yea those look like something you want to use.
The good thing about even normal PSU's from meanwell (like the MeanWell HRP series) is that htey have the possible to adjuast the output voltage (The HRPG-1000-12 can be adjust to a maximum of 14V i.e. and features constant current limiting -> requiement for charging batteries)
Yes, the NPB is the newer model. However, it doesn't have the small pot to adjust the voltage. You can use some presets, but for all other settings you need the optional SBP-001 programmer.
I bought DPS800GB and make hack found on YT (
) to disable over charge protection and voltage change. I've tried to charge my LifePo4 with it and here's the result
With 14.1V set on charger and battery around 13.4V - there was some constant clicking inside and current was low - around 30A
With 13.8V charger and 13.4V battery - 85A charging but charger was getting really hot, and after 10-15minutes current dropped to 35-60A, and it was floating (probably some protection)
Is there a way to limit current from the charger? Running it at 100% is really bad idea.
With 14.1V set on charger and battery around 13.4V - there was some constant clicking inside and current was low - around 30A
With 13.8V charger and 13.4V battery - 85A charging but charger was getting really hot, and after 10-15minutes current dropped to 35-60A, and it was floating (probably some protection)
Is there a way to limit current from the charger? Running it at 100% is really bad idea.
MarcoWasRight
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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.
