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40 Amp Shore Power Charging, With A $12 Server Rack Power Supply

A.Justice

Swears he didn't start that fire.
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I'm going trailer camping in a few days, and I wanted a shore power connection for my trailer (180 ah, 12 volt, LiFePO4) without spending much, because I won't use it very much. I already had a 40 amp Renogy DC-DC charger, so I figured I would use that as a starting point.

I found a pair of 750 watt, 12 volt, Dell redundant server rack power supplies on e-bay for just under $24. That's 1.5 kw of 12 volt DC action. There was a YouTube video about which pins to bridge with solder to get it to power on, and to slow the fan to half speed (full speed fan on it is very loud). It was incredibly easy to do.

I hooked one with soldered wires into the DC-DC charger, added a switch (really just some blade connectors) to the starter sense wire because if you power the server supply on and the DC-DC on at the same time, the PSU can't deliver power instantly and the converter gets an error, so it needs a few second delay to let the PSU start, then switch on the converter.

Just thought I would share my incredibly cheap (if you already have a DC-DC converter) shore power method.

I'm waiting on 50 amp fuses before I actually install it in the trailer, I know it's not exactly safe in the photos.
 

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It's certainly an option if you're fully DIY.

You can get some pretty substantial power output from old power supplies. Especially if you can get them cheap or free.

Definitely the route I would take on a limited budget.
 
I'm going trailer camping in a few days, and I wanted a shore power connection for my trailer (180 ah, 12 volt, LiFePO4) without spending much, because I won't use it very much. I already had a 40 amp Renogy DC-DC charger, so I figured I would use that as a starting point.

I found a pair of 750 watt, 12 volt, Dell redundant server rack power supplies on e-bay for just under $24. That's 1.5 kw of 12 volt DC action. There was a YouTube video about which pins to bridge with solder to get it to power on, and to slow the fan to half speed (full speed fan on it is very loud). It was incredibly easy to do.

I hooked one with soldered wires into the DC-DC charger, added a switch (really just some blade connectors) to the starter sense wire because if you power the server supply on and the DC-DC on at the same time, the PSU can't deliver power instantly and the converter gets an error, so it needs a few second delay to let the PSU start, then switch on the converter.

Just thought I would share my incredibly cheap (if you already have a DC-DC converter) shore power method.

I'm waiting on 50 amp fuses before I actually install it in the trailer, I know it's not exactly safe in the photos.
i have the same setup 1000 watt hp power supply works well 60 amp Renogy DC-DC charger only thing is the output gets hot. does your also gets that hot. i use 25mm2 cable and good terminals
 
Which powersupply?

I've seen some powersupplies which depend on the chassis they are installed in for (additional) cooling. Not all have internal fans, and while some have, I've noticed the outer case is sometimes also used as heatsink, assuming there is sufficient airflow in the chassis to cool the casing as well.

And also note, a 1000W powersupply for a 60A DC-DC is running at pretty high loads. Depending on the SOC the voltage at the secundairy side of the DC-DC is 13-14V.

60A @ 13.5V = 810 watt. Add 90% efficiency of the DC-DC, the primary draw would be 950 watt..
and at the primairy side thats at 12V thus almost 80A. Requires decent connections and cable lugs. For a server powersupply I would solder multiple wires in parallel to handle that current

Generally, server power supplies can provide their rated output, but do get very hot. In reality, it's normally running at lower loads, and the 1000W is only the peak load (eg running GPU/disks at full load)
 
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Which powersupply?

I've seen some powersupplies which depend on the chassis they are installed in for (additional) cooling. Not all have internal fans, and while some have, I've noticed the outer case is sometimes also used as heatsink, assuming there is sufficient airflow in the chassis to cool the casing as well.

And also note, a 1000W powersupply for a 60A DC-DC is running at pretty high loads. Depending on the SOC the voltage at the secundairy side of the DC-DC is 13-14V.

60A @ 13.5V = 810 watt. Add 90% efficiency of the DC-DC, the primary draw would be 950 watt..

Generally, server power supplies can provide their rated output, but do get very hot. In reality, it's normally running at lower loads, and the 1000W is only the peak load (eg running GPU/disks at full load)
power supply is cool input cables stays cool only thing is the output of the renogy gets hot after 1 min of pressing your finger on the terminal you WILL remove it.
yes it needs to boost convert it will go to 14 v
read some where on this forum that a victron dc-dc also gets very hot
 
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power supply is cool input cables stays cool only thing is the output of the renogy gets hot after 1 min of pressing your finger on the terminal you WILL remove it.

is it the Renogy itself which gets hot, or the terminals? If its the terminals I would suspect the cable lug or crimp. As with any other high-current path, sand it slightly with high grit paper (2000 or so), and a decent clean, and torque according specs.

Also make sure the cable lugs are properly crimped.
 
i have the same setup 1000 watt hp power supply works well 60 amp Renogy DC-DC charger only thing is the output gets hot. does your also gets that hot. i use 25mm2 cable and good terminals
Mine gets hot on the input wiring, ironically, it's the two double strands from the power supply to the DC-DC that heat up, and not the longer single strand to the battery. I think it's because of the 3 very large fans blowing hot air directly on them.

The step up from 12v to 14.1 (I have mine set there) generates a higher amperage, I did some testing and math and got 39 amps at 14.1v to the battery, and more than 50a from the PSU to the DC-DC, but that's because of the step up, and some losses. My PSU is almost maxed out. I have a second one I can parallel.

I use 10 awg 200°c silicone wire for both runs, and 40a at that length preforms great, it's a little bit warm after 3 hours of sustained 40a charging from the DC-DC to battery. Check a wire size chart and size up 30-40% to keep it cool, or double up with identical wires.
 
One thing to consider is these supplies output EXACTLY 12V… so, boost converting may be needed.
For anyone else reading this thread:

That's why the DC to DC charger is necessary.

You could use an adjustable boost converter but that wont provide any kind of charge control.
 
166 euro incl shipping

Same one is sold on the Ective brand:

I have the Renogy 40A, bought at their German store, they do ship to NL.

I didn't opt for the 60A, since I don't want to put too much load on my alternator. Alternators don't like running at high loads for longer times, and since mine is only 120A, I wanted to keep its load low, even with all car-related equipment drawing from the alternator as well. Especially in a traffic jam on a hot day (with less wind due to driving speeds) I want the alternator not to overheat.


I have a Meanwell 24A Charger (source: Conrad), and a Meanwell RSP-1000.
The RSP-1000 isn't a charger, but a powersupply with CC limiting, so it can be used as a charger, but it does lack the charging profiles. I use it to initially charge cells before balancing, it provides 60A. Can't be run unattended due to lack of charging profiles, but it's a cheap solution. And it's relatively easily to boost the 12V output to approx 14.1 (Can't get it higher - overvoltage kicks in).
Bought it used for 25 eur at Marktplaats
 
but the Renogy you can set to half amps so a 60 amp becomes 30 amp
but i still need to connect it to my alternator.
 
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but the Renogy you can set to half amps so a 60 ah becomes 30 ah.
but i still need to connect it to my alternator.
Please explain this feature.
And I’m sure you meant Amps, not Ah… since Ah is a quantity of energy storage, not production.
 
Please explain this feature.
And I’m sure you meant Amps, not Ah… since Ah is a quantity of energy storage, not production.
That series of Renogy DC-DC converters has a sense wire, and if it's connected to starter battery positive, will cut the rated charging amperage in half.
 
Yeah but that's not what he meant lol
yes this is what i meant. sorry for my English.

but on the other hand why not use your scc and your lab power supply 10 amp at 30v gives you 21 amp at 14v also done that. set your float to 14v else your voltage and your current will drop to soon.
also make sure that you have a 30 amp mppt scc and your solar disconnected.

connect every thing together 60 amp dc-dc and 21 amp scc gives you 81 amp.
and suddenly i realise i want to charge with even more amp to charge these things.
 

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but on the other hand why not use your scc and your lab power supply 10 amp at 30v gives you 21 amp at 14v also done that.
For some reason the Victron 100/30 doesn't like my bench power supply. It makes it hiss as it tries to find it's power point.
 
For some reason the Victron 100/30 doesn't like my bench power supply. It makes it hiss as it tries to find it's power point.

That means your powersupply isn't providing enough juice.

A 30A MPPT, with a battery which is at approx 13.3V, requires 400W of power. Take 95% as efficiency for the MPPT means it requires at least 420W at the primairy side.

Since a MPPT wil 'hunt' for the maximum available power, it potentially will try to pull that 420W. Using a 30V power supply makes you need it capable of providing 14A.

If it's only providing 10A, it needs to have current limiting, and not just shutting down on overload. However, due to the nature of a MPPT, it might be the MPPT algoritm interferes (/is faster) than the current limiting of the PSU, causing it to flap and never find a proper point to actually start working.

To be on the safe side, make sure the powersupply is capable of at least 30A x 14.6V (maximum on paper with all cells at 3.65V) = 440W, add 10% for the MPPT, so go for 500W.
Also, make sure the powersupply provides at least 20V, since the MPPT requires battery voltage +5V to start working.

Maybe you can limit the MPPT to a lower than 30A setting, that might work with a smaller powersupply.
 
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