Charging SP140 battery pack from camping car's 12V system

Power System
1

Hi Guys,
I am often on the move with my camping car, and I would like to know the best way to leverage the power system on-board my camping car. I have a 1500W inverter connected to 400Ah of lithium 12V batteries. In theory I could plug the 1000W charger I bought with the unit on this, but that would be highly inefficient…
Therefore, I was wondering if it is possible to connect the battery pack directly to a DC-DC step-up converter like this:

Anyone has an opinion on this?

2

Start with the math.
400ah X12V is 4800Watt hours
I thiink the SP140 battery is just aroud 4Kwh or 40000 watt hours. Your 1500watt inverter can move 1500 watt hours each hour. Is that voltage step-up rated for 15amps at 12v or 15amps at 96v?

Its like draining one bucket into a slightly smaller bucket though a small hose. To charge the sp140 battery, you’ll probably need something bigger.

3

I did start with the math. My reasoning is as follows:

  • I go out with a fully charged set of batteries.
  • After 1 or 2 flights, I have used ~50% of SP140 battery.
  • I only need to use ~40% of camping car’s 4.8KW to charge the SP140 2KW.
  • The DC-DC convertor is rated at ~1.5KW (96V @ 15A) with 96% efficiency, so it should take under 1.5 hours to recharge the 2KW.

Now that the math is cleared up, my simpler question is: is it safe to plug the SP140 battery pack into this DC-DC convertor? Will the BMS be able to intelligently manage the current draw from this DC-DC system?

1 Like
4

Sounds like your specifications are good. Is that DC step up rated for that power continuously or does it have a much more limiting duty cycle?

If your flying only 50% of the sp140’s battery capacity it’ll last a very long time. Charge it to 90% and take it down to 40%.

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5

It seems to be rated for that power continuously, with a huge heatsink to boot.
So basically, if I feed that DC 96V to the battery pack (with the booster’s 15A limitation being applied), the BMS will know that it is safe to get charging, right? (there is no need for some digital handshake signal being passed through).

6

No digital handshake, although you won’t fully charge it at 96v.
The pack can handle 15A input.

If you have the newer pack with the Bluetooth BMS you should see all the important stats on the app.

7

I have been using one of these for two years now to charge my SP140 pack off solar.

I run the 36V solar input directly to the boost converter, and I have the setpoint for 100.8V.
I charge at about 3-4amps which is the most the Boost converter can handle even though its “rated” at 40A.

The module says 90V, and I’ve noticed the newer ones in fact only go to about 90-65V. But I have a box full of older ones which had no restriction and max out right at 100-102v. The end range of the pot is very sensitive.

8

reminder: you’ll be drawing a 125 amps @12v to hit 1500watts. lithium should take that but just make sure.
chances are it’s not rated for 96% efficiency, You’ll most likely deplete more than you think.

For my camper setup:
I’m running 10KWh battery @24V into MPP Hybrid solar inverter. It has 120v output. I’ve also used my battery to connect to solar input to drain the battery back into the camper battery. Growatt is another one. not sure if they have 12v options though.

you could just go with a 12v-120vac inverter and run the stock charger? you could run a bunch of other 120v off it too. Solar inverter with battery | Battery power inverter. this way you have a safety built in for low voltage cutoff if your lithium doesn’t have a BMS?

9

Thank you all for the useful information. I confirm that my RV is running on Lithium Batteries, and that they have a built-in BMS. So it all should be good to go!