Power Station Build not performing

[CamperMaverick]

Hi all,

I built my first power station for a camper platform for my Ford Maverick. I'm having performance issues. I'll explain the issue, share the specs, the things I know I need to fix anyway (but I don't think are causing the issue). Would love your feedback, and anything else you notice as well.

The issue: battery drains much faster than expected. I have a load that, when maxed out, pulls 1800 watts. But even well before maxing it out (pulling around 900 watts), it's crushing the battery. For example, the battery was at 13.0 volts, which is 30% according to LiTime manual. Running the load at 900 watts for about three minutes brought the battery to 11.5 volt, which according to the manual is approximately 4%. Given the battery's capacity (2560 watts), my understanding is that it should have around 768 watts left. And a load of 900 watts for three minutes should really only drain around 45 watts. Granted it's an inductive load, but should it really crush the battery that much? It'll recover a bit afterwards, but is still drained substantially. I'm mostly monitoring it using Renogy's DC Home app and the BT-2 module. "Beeps" from the system indicate the struggle is real.

Specs:
Two 12 volt 100ah LiTime batteries, wired in parallel with two 4 gauge wires (didn't have the room for 1/0 so tried doubling up as it's also what Renogy does with Inverter)
2000 watt Renogy Inverter
50 amp Renogy DC-DC On Board Battery Charger with MPPT
15 amp AC charger
12 volt, 100 ah fuse block
Everything was bought from OfferUp, which certainly could cause it. Batteries were new in-box though. Tested everything else, except AC charger, which has been working fine.

Known issues/planned improvements:

• Batteries are wired with two 4 gauge wires between positive posts, and negative posts, respectively. Only one four gauge wire from batteries to bus bar, and bus bar to inverter. Need to add wire from battery to bus bar, and bus bar to inverter
• Add fuses!
• Route out space below heat sink of DC-DC charger to allow more space
• Clean up wiring
• Plugs for fans when not in use
• Need to add fuse box cover

I've attached a picture of the inside of the box (it's siliconed and screwed shut now), and some shots in the wild for fun. And I know, an induction load is very demanding and not necessary for my build, but this build was/is also about learning for me for bigger projects in the future. As stated, this was my first build.

 

[chrisski]

If you doubled up 4 AWG, that is about equivalent to 2AWG, so 4 strands may help.

I disagree with doubling up on wire if it can be avoided.

Seems at some point there is not double 4AWG.

4 AWG wire has ampacity of around 100 amps, and the inverter is pulling close to 200 amps with DC losses. My guess is the 4AWG wire is getting close to melting which is additional amps lost. That is we’re I think your mystery power goes.

 

[CamperMaverick]

I agree, doubling up wire wasn't ideal, but working in pretty tight space.

The longest run is about 12 inches, so I was hoping that minimized voltage loss as well. It hasn't gotten much use though and I'm wondering why the power loss is so high even when I'm pulling only 900 watts/8.5 amps which is well within 4 gauge range

 

[chrisski]

I agree, doubling up wire wasn't ideal, but working in pretty tight space.

The longest run is about 12 inches, so I was hoping that minimized voltage loss as well. It hasn't gotten much use though and I'm wondering why the power loss is so high even when I'm pulling only 900 watts/8.5 amps which is well within 4 gauge range

I’m confused. 900 watts at 12 volts with inverter losses is close to 85 amps, which will exceed the ampacity of wire unless the insulation is 90 degrees

900/12/.85=85 amps

 

[CamperMaverick]

Sorry for the confusion. On AC the device is 900 watts. I'm measuring it after the inverter.

 

[chrisski]

Sorry for the confusion. On AC the device is 900 watts. I'm measuring it after the inverter.

What wires go into the inverter and leave the battery? If those are 4 AWG, that could be an issue.

 

[CamperMaverick]

Paralleling the batteries = 2x 4awg
Batteries to bus bar = 1x 4awg
Bus bar to Inverter = 1 x 4awg

If I was pulling the full load, say 1800 watts on AC, the under sizing of wire makes sense to me, though I’m surprised it’s so drastic. But at half that, it doesn’t seem like it should cause that much of an issue. Or am I wrong on this point?

 

[CamperMaverick]

PS thank you for your replies

 

[grizzzman]

Sorry for the confusion. On AC the device is 900 watts. I'm measuring it after the inverter.

Chrisski was showing you the math showing how many amps at 12 volt using 900 watts on the 120 volt side

 

[grizzzman]

We're you using a charger during the event?

 

[CamperMaverick]

No, was not using any charging when loss occurred.

And I understand what he was saying now, the draw on the battery side was 85 amps. This wire chart for 12 volts seems to indicate that that is well within the range of the wire gauge: http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/#google_vignette

 

[Rednecktek]

No, you're right, 85 or 90a across a short length of 4AWG should be fine. It sounds more like a bunk inverter. Since I'm assuming you don't have a spare inverter available, a test you can try is to either double up the wires to the inverter, or if physics allows pull the doubles off one of the batteries and connect those to the inverter temporarily then re-test the load. The battery should allow 100a easily through its BMS so if the inverter still throws a fit at 1000w then it's the inverter. If the voltages don't drop out and it runs fine then you'll need to get more copper between the batteries and inverter. Keep loading it up and worst case is that around 1200w the BMS trips. Not a worry as it'll reset when you connect it back to the rest of the system.

Your voltages also sound low, you may just be bottoming out on the battery. Make sure it's all fully topped up before you run the tests just to rule out the simple answer of "The batteries are dead".

 

[CamperMaverick]

Thank you, I appreciate the "testing" advice. Leaving today for a trip so I'll be keeping everything on low for this one, and then doing diagnostics on the way back.

And I was surprised the LiTime manual says its max voltage is 13.5, I thought typically they'd be higher than that. Anyway, I've had the thing plugged in to my AC charger so it's fully juiced for the trip. Let's hope it goes well!

 

[grizzzman]

Thank you, I appreciate the "testing" advice. Leaving today for a trip so I'll be keeping everything on low for this one, and then doing diagnostics on the way back.

And I was surprised the LiTime manual says its max voltage is 13.5, I thought typically they'd be higher than that. Anyway, I've had the thing plugged in to my AC charger so it's fully juiced for the trip. Let's hope it goes well!

The're site shows 14.4 at 13.5 it is not likely the battery will ever get full let alone get the passive balancer's time or proper voltage to do there thing.....