Minimal system to charge 48v battery from 48v battery?

[jameshowison]

RV site completely shaded.

Considering a small mobile system, maybe on the truck tow vehicle, maybe on a dolly. An MPPT and a battery, wheel to sunny spot, lay out panels, harvest sun.

Now you have a full 48v battery and return to the RV. How to charge the RV battery?

Can this be done with the MPPT “in reverse”? But seems it would need +5V above the battery level?

A 48/48 DC to DC (Orion)? Those seem limited to ~400w which is slow.

If you just hook the battery into the RV system in parallel that’s fine but I’d rather dump the power into the RV battery more quickly.

 

[wme]

https://www.amazon.com/Converter-DR...c+adjustable+converter+step+up,aps,229&sr=8-3
Maybe something like tihs?
Maybe parallel a couple?

 

[pollenface]

Boost converter set to bulk/absorption voltage + watt meter to monitor current/wh dumped.

I have one of these keeping my 48v bank @ 52.2v overnight, it charges from a 12v bank.

1200W 20A DC-DC Converter Boost Car Step-up Power Supply Module 8-60V to 12.ac g | eBay

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[AntronX]

You need a buck-boost dc-dc converter to do it efficiently. I am not aware of a commercial device to do this. You may have to build one using buck-boost controller IC and design your own circuit for it or take a reference design in the datasheet. Another simple but inefficient solution is to use an dc-ac inverter and ac-dc charger.

 

[crossy]

How about one (or more in parallel) of these chaps https://www.aliexpress.com/item/1005005713589961.html

 

[crossy]

@pollenface looks like great minds think alike

 

[HarryN]

One possible approach would be to attach a 2 kW inverter to the mobile 48 volt pack.

Then plug the RV into this inverter to charge the RVs battery pack.

This concept is used quite a bit in conversion vans to pull power from the 12 volt alternator and charge for instance a 24 or 48 volt pack. Of course people also used DC - DC converters but this method is also popular.

_________________

If the sunny location is within a few 100 ft, then another path is to run a long 10 awg solar wire from the panels to the RV directly.

Yes there will be voltage drop / losses from the long wire run, but this can be dealt with.

For example - suppose you have a 150 / 35 victron solar charger or similar.

Wire the panels so that the array has ~ 100 - 120 volts Vmp. Essentially the voltage of one panel is being used to make up for the losses of the long wire run and the rest goes into charging.

(80 volts actually reaching the RV ) x ( 20 amps ) through a PV wire is still a fair amount of power.

 

[jameshowison]

One possible approach would be to attach a 2 kW inverter to the mobile 48 volt pack.

Then plug the RV into this inverter to charge the RVs battery pack.

This concept is used quite a bit in conversion vans to pull power from the 12 volt alternator and charge for instance a 24 or 48 volt pack. Of course people also used DC - DC converters but this method is also popular.

_________________

If the sunny location is within a few 100 ft, then another path is to run a long 10 awg solar wire from the panels to the RV directly.

Yes there will be voltage drop / losses from the long wire run, but this can be dealt with.

For example - suppose you have a 150 / 35 victron solar charger or similar.

Wire the panels so that the array has ~ 100 - 120 volts Vmp. Essentially the voltage of one panel is being used to make up for the losses of the long wire run and the rest goes into charging.

(80 volts actually reaching the RV ) x ( 20 amps ) through a PV wire is still a fair amount of power.

Thanks all!

We do have a good extension cable, but often need to go further or across a road. Even a little traffic seems too much. But yeah, longer cable will help.

 

[jameshowison]

@pollenface looks like great minds think alike

Thanks!

I’m not entirely following why a booster is needed? This is 48v to 48v (ie not boosting from 12 or 24).

But is it to boost the voltage high enough (eg +5v or so) to drive the MPPT to charge the RV battery? Maybe that was obvious to others

 

[billvon]

Thanks!

I’m not entirely following why a booster is needed?

Because if you just connect them, then they will equalize, but will not move energy from the mobile battery to the RV battery after that.

 

[jameshowison]

Because if you just connect them, then they will equalize, but will not move energy from the mobile battery to the RV battery after that.

Ah, so the booster would always keep the voltage coming from the donor battery higher and therefore power would keep flowing.

Got it, thanks!

 

[ejfluhr]

>If you just hook the battery into the RV
>system in parallel that’s fine but I’d
>rather dump the power into the RV
>battery more quickly.

If you are building a new mobile system, and the RV battery is readily accessible, then one action could be to physically swap the RV battery for the newly recharged battery. That is the fastest "transfer" with least loss in power.

Buck/boost is still valuable in that situation for topping off from one battery to the other...

 

[Crowz]

A user on here asked about this charger earlier :

https://www.amazon.com/dkplnt-Converter-Commercial-Vehicles-Ignition/dp/B0B1MVW5WW/ref=pd_ybh_a_sccl_26/144-5657782-3600639?pd_rd_w=nTiXQ&content-id=amzn1.sym.67f8cf21-ade4-4299-b433-69e404eeecf1&pf_rd_p=67f8cf21-ade4-4299-b433-69e404eeecf1&pf_rd_r=ZERPN8TXW7NBE9KJWSZD&pd_rd_wg=aVyCe&pd_rd_r=b4671dc3-f782-4385-b8c4-e876a0dbe0ba&pd_rd_i=B0B1MVW5WW&th=1

No one was able to find any info about it but if it does what it "claims" to do it sounds like its worth looking into.

 

[Crowz]

You mentioned 400 watts being to slow and the thing I linked isn't but 580 watts so thats probably to slow too.

 

[timselectric]

Quick and simple.
Inverter and chargeverter.

 

[timselectric]

PS $1k

 

[jameshowison]

PS $1k

True story. But also one would loose like 10-20%, on the trip from DC to AC to DC, no?

 

[timselectric]

True story. But also one would loose like 10-20%, on the trip from DC to AC to DC, no?

Maybe
But it definitely wouldn't be charging too slow.

 

[jameshowison]

Maybe
But it definitely wouldn't be charging too slow.

Yeah, I’m thinking this is a good application for an all in one solar generator as the truck/remote system. Plug the 30amp in, charge the RV batteries, all done. And then useful mobile system rest of the time.

 

[pollenface]

Ah, so the booster would always keep the voltage coming from the donor battery higher and therefore power would keep flowing.

Got it, thanks!

Like water flowing from a high bucket to a low bucket.