Auxiliary Battery Plan - Please Review

[Rubiland]

I'm adding a 50AH LiFePO4 auxiliary battery to my vehicle to power my Dometic CFX 50, LED camp lights at night, charge mobile devices, and such.

I'm going to use the Renogy RBC50D1S to charge the battery from my alternator and solar panel(s).

This is the diagram I've put together so far, do any "experts" see any problems or am I good to go? (Thanks in Advance!)

Also, any problems with just cutting off the 12v lighter plug and putting cables directly to the Blue Sea ST Blade? I'm guessing not, there will be a 10Amp fuse and the distance is not longer than the OEM cable.

 

[Rando]

I don't think you need or want a 50A DC-DC with a 50Ah battery - it would live a shorter than expected life. Use a smaller 20A DC-DC, then you can also save money and weight on the cables and go with 10 or even 12AWG.

 

[Rubiland]

I don't think you need or want a 50A DC-DC with a 50Ah battery - it would live a shorter than expected life. Use a smaller 20A DC-DC, then you can also save money and weight on the cables and go with 10 or even 12AWG.

I didn't take into account the charge rate, forgot that. I'm interested in having a DC to DC charger with on-board MPPT controller to cut down on devices and wiring. I'm going to update the drawing to reflect using the 30Amp charger. After some research I found that the mfr suggested a C/2 charge rate as optimal, but also suggested with a C1 discharge and C/1 charge rate, you still get 3000 cycles, but will be at around 75% capacity. My plan is to not discharge the battery more than 80% when alternator charging isn't possible, but I suspect the solar should assist with never getting that far down in charge anyhow.

Thanks for catching that and pointing it out. I'm going to update the drawing and re-post.

 

[jonathon]

No issues cutting the fridge cord and hard wiring it to a fused circuit. I did that with my ARB, except I used Anderson Power Poles so I could keep it flexible. The factor fridge cable is only 16 gauge.

 

[Rbertalotto]

I don't think you need or want a 50A DC-DC with a 50Ah battery - it would live a shorter than expected life.

Are you sure about this....My understanding is Amp Hours has nothing to do with charge capacity. The DC to DC charger is "Smart" and will limit charge current based on voltage of the charging battery. I'd call Renogy before you downsize.

 

[dreadlocks]

LiFePo4 Cells should not be charged more than 0.4C rate if you want em to last, this is standard industry knowledge.. They will however take far, far more than that charge rate if you do not limit it.. if you hook up a 50A DC-DC charger to a LFP battery it will charge at 50A regardless if thats within the batteries specs.

Should use a 20A charger with a 50A LFP.

 

[jonathon]

LiFePo4 Cells should not be charged more than 0.4C rate if you want em to last, this is standard industry knowledge.. They will however take far, far more than that charge rate if you do not limit it.. if you hook up a 50A DC-DC charger to a LFP battery it will charge at 50A regardless if thats within the batteries specs.

Should use a 20A charger with a 50A LFP.

I was just going to ask about that and now I think I get it. Thank you!

 

[Rando]

Are you sure about this....My understanding is Amp Hours has nothing to do with charge capacity. The DC to DC charger is "Smart" and will limit charge current based on voltage of the charging battery. I'd call Renogy before you downsize.

I am sure about this. The charger will charge at whatever it's current limit. As far as I know this is not adjustable on the Renogy units. Charging at 1C is not going to do major harm to the battery, but might shorten it's life a little, and ups the requirements for wire gauge and everything else. If you are designing this to be 'optimal' then you want either a programmable DC-DC where you can specify the current (Victron), or a 20-30A one that won't stress the battery so much.

 

[Rubiland]

So, after some thought, I actually think I may go a different direction and see if I can save some money, weight, and work...

I'm going to start off with a 160w solar panel with a MPPT controller. I'm not running any heavy loads and I think the panel can keep up with my energy needs. If necessary, I can add a second panel.

I do have a few questions though:

• I don't think my loads are going to be any where near 20 amps (not amp hours), is it ok to pull the load through the Victron so I can make use of the built in reporting and usage monitoring?
• Is it ok to ground the battery to the chassis or should I connect the negative to the starter battery?
• From the solar panel to the charge controller should be less than 10', can I use 12AWG wire?
• From the Battery to the charger will be less than 2', can I use 12AWG?
• Is the fuse in the victron sufficient or do I need a fuse down at the battery?

Thanks again for all of your help!

 

[dreadlocks]

If properly cycled Lithium cells will last for 15 years on Mars (>5k cycles), imagine how long you could get em to last here with a more friendly environment.. follow the suggested guidelines, at 0.4C charge rate you can get em from totally flat to full in 2.5h, which is already absurdly fast compared to other chemistries.. charging it in an hour flat is rather overkill for most needs and given cost I would think most would like the longer service life.

 

[dreadlocks]

• I don't think my loads are going to be any where near 20 amps (not amp hours), is it ok to pull the load through the Victron so I can make use of the built in reporting and usage monitoring?
• Is it ok to ground the battery to the chassis or should I connect the negative to the starter battery?
• From the solar panel to the charge controller should be less than 10', can I use 12AWG wire?
• From the Battery to the charger will be less than 2', can I use 12AWG?
• Is the fuse in the victron sufficient or do I need a fuse down at the battery?

• Sure
• Chassis is fine, the charge source (alternator) is block/chassis grounded.. Adding some redundancy may be wise.
• Sure
• Sure
• No, always fuse at the battery.

 

[vomhorizon]

I'm building a portable power pack using a 50 Ah lithium battery that will be self contained in a box. All the connections will go via a fuse block (also in the box) and the battery will itself be fused at the terminal and the power connection to the fuse block mounted via a 50 Amp breaker switch. The battery will charge via a vehicle mounted, switched, DC-DC charger (0.4C) connected to it via an anderson plug . Would I need to consider an option to ground the portable battery (If so any ideas on how best to do it while still keeping it portable) or should I just treat is as an isolated system like an Arkpak or Goal Zero?

 

[dreadlocks]

just treat it as an isolated system, should be getting ground from its charge source.. and everything running off it should be getting ground off the battery directly.