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I'm not all that knowledgeable when it comes to advanced electrical engineering, so I'm asking for some advice here.

Here's my problem:

We have several mobile refrigeration units that are powered by batteries (eight 12V AGM batteries wired in series to 48V). The problem is that the built in inverter on this unit won't initiate charging when battery voltage falls to a certain level. It's a design flaw that's not likely to be rectified anytime soon. What I've been doing to temporarily rectify the situation is take two 24V vehicle jump-starters, connect them in series to 48V and connect them to the unit's batteries via jumper cables to effectively "jump start" the system. Once the inverter sees the battery voltage high enough, it will start the charging circuit, I can disconnect the jump starter and go about my day.

What I want to do is design a type of jump starter that doesn't rely on batteries.

I'm looking at using this power-supply for this purpose: MeanWell SE-1500-48

However my concern is the inrush current when first connecting to the discharged batteries. I measured it with an amp-clamp, and with batteries that aren't even fully discharged, I'm seeing a 30amp draw for about 5 or so seconds at which point it begins to ramp down to a nominal 7 amps after about 15 seconds. That's obviously going to exceed the limits of the above power supply. Rather than selecting one that's a lot bigger (and will then require 240VAC input) can I use some sort of inrush current limiter? It seems simple in theory but there's so many to choose from, I have no idea which one to buy.

This one looks like it might work but the rating is 120VAC and up. Would this not work for a lower voltage DC application?

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  • \$\begingroup\$ Is it possible to disconnect the battery bank, connect some sort of low cost power source to the inverter so that it sees high voltage, then connect it back to the batteries? I'm not sure this might work, and the refrigeration unit should be off while you do that, that's just an idea. \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 13:00
  • \$\begingroup\$ Also I don't quite understand why you say the termistor won't work for voltages below 120V \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 13:05
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    \$\begingroup\$ Eight 12V batteries in series for 48V? Do you mean two sets of four 12V batteries wired in parallel? 12*8 = 96V if they were all in series. \$\endgroup\$ – sherrellbc Jul 18 '14 at 13:25
  • \$\begingroup\$ Try it and see unless your are sure there'll be some damage done. \$\endgroup\$ – Andy aka Jul 18 '14 at 16:48
  • \$\begingroup\$ Sorry. I meant that there's 8 batteries in total. Each bank is 4 batteries wired in series, then both banks are wired together in parallel. @VladimirCravero, the reason I say I'm not sure if it will work, is simply because I don't know any better. I'm looking for confirmation. \$\endgroup\$ – Joseph Toronto Jul 18 '14 at 17:30
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It looks like the Meanwell supply might work as is. Have you tried it?

I don't know how they behave if the load is too small (too much current.) If you got a bench supply, (some cheap Mastech maybe), then when it starts it will just go into CC mode (constant current) and maybe work just fine.

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  • \$\begingroup\$ That's what I thought but as per the spec if max current is exceeded the PSU shuts off and need to be manually restarded. In the specs there's also written that max current is 31A and that all their PSU can withstand an overload between 105% and 125%. There's too little tolerance IMHO, OP should better use the thermistor. \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 14:31

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