External Li Battery Upgrade Install Concept

[K7MDL]

I finally made some decisions and started working on my Li conversion. I diverge from most installs here by mounting the DC-DC charger under the back of the cab. It is IP67 rated with BT control and configurable up to 50A with MPPT solar built in. It replaced the ACR I had mounted there. The existing output wiring goes to 2 locations:
1. Back of the cab interior where my radio gear is (6AWG)
2. Normal camper Attwood connector mounted in my truck bed which is 6AWG down stepped down to the 10AWG of the connector and the stock 10AWG camper wiring.

My radio gear draws high current and does not tolerate much voltage drop. Nothing in the camper draws much current or cares too much about a little voltage drop except for battery charging current. On Li the furnace should be happy at all times.

My existing AGM batteries are near my rear bumper and will be removed saving a lot of rear axle weight. The Li battery will be tested in 2 locations, both up forward cutting the total wire length to 2/3rds reducing voltage drop

Location 1: The Li battery will reside under my back seat about 4 wire feet to the DC-DC charger and 1-2ft to my fused distribution panel. All the high charge and discharge currents are within the 4 feet of wire in my cab and the total charging wire length is shorter and larger gauge than if located in the camper. I should be able to see 40-50A charge rates. The appliance and lighting loads of the camper are relatively low so the 10AWG stock camper wiring is suitable, there is no battery charge current. I would want to run the solar panel (PV) wiring to the under-cab DC-DC charger MPPT input (deferring for now pending the location testing below). That will also trickle charge the starting battery. Other than the solar wire routing outside, the camper stays all stock.

Location 2: Place the Li battery in the front corner of my front dinette camper under the driver side seat and test the voltage drop to the radio gear into the cab. Given the higher voltage of Li and the now shorter total wire length compared to the rear located AGMs, it may overcome the V-drop of the mixed 10/6AWG cable run and keep my radio gear happy. The charge rate will be reduced relative to the cab location (configured to 20 to 30A max) but I can keep the solar charging wire completely within the camper. The existing Overland Solar MTTP 100|15 charger, which appears to be a rebranded Victron, is supposed to have a Li preset as noted in the Victron version manual (and User defined also). Upsizing the camper wiring would be a last step on this if needed, not sure it is needed so far.

Waiting for the right size crimp ring terminals to arrive to begin testing Location 1. Camper will come out of the garage and onto the truck in a month and can then test location 2 then.

- Mike K7MDL

 

[K7MDL]

Got it wired up today and tested with a 50Ah LiFePO4 battery in the cab.

6AWG from the starter battery (via 60A breaker) to the IP67 rated DC-DC charger under the right rear of the truck.

Output is 4ft 6AWG to a 75A Anderson splitter then 18" 8AWG to the fused battery. The splitter also feeds though 6" 10AWG SuperPowerGate battery isolator/charger for a 7Ah AGM (decided to leave it in place) and its output feeds a PowerPole distribution fuse panel and my radio gear with peak loads up to 32A total. That wiring is 12AWG and varies from inches to 2.5ft.

I set the charger output for 50A max charge limit and started the truck up to measure voltage drop and see what charge rate I could get. The battery is partially discharged for storage.

Answer is 32A charge rate with 0.9V drop between the starter battery and the charger. 13.7V input to the charger, 14.6 output from the charger. I suspect the alternator was the limiting factor but not sure yet since the voltage did not drop. Was hoping to see a higher charge rate. Battery can accept up to 50A. I decided to set the charge rate limit to 30A anyway.

I did not measure the voltage at the radio gear but there was only 2A load so would not be much drop. When I install the high-power VHF amps then I will get a measurement. They do not like low voltage but are happy on the Li battery alone.

In a month I will put the camper on the truck and 2 things.

1. Set the charger for AGM and see what the charge rate and voltage is at the existing pair AGMs now in the back of the camper. Lots of 10AWG wire. I have seen 19A max with previous standard setup.

2. Disconnect the AGMs and relocated the Li battery from the cab into the camper front driver side under dinette seat box and tap into the existing ACR and see what the total voltage drop and charge rate the stock 10AWG camper wiring can yield. Additionally measure the voltage at the radio gear.

Based on the above can leave it as is, upgrade the camper side wiring size, or put the battery back in the cab and call it done. Probably put a 100Ah battery in as I use the 50Ah for my microwave radio field work.

If the battery stays in the camper I can use the existing solar charger set to LI profile. If it goes in the cab then I will run the solar panel output wiring outside the camper and down under the truck to the charger MPPT input. That has the advantage of trickle charging my starter battery. I have a high parasitic starter battery drain, 2 weeks and I have a dead battery, so this solution is most desirable from that perspective.

 

[K7MDL]

I have identified a problem with keeping the battery in the cab. Condensation.

It is on the floor under my rear seat. I checked the battery in the morning and it was very wet. When the daylight hits the battery does not worm up as fast as the rest of the truck, it has also been humid here. Could wrap it in foam.

I think I will wait until I put the camper back on and install the battery in the front corner near the cable entrance and see how it does with the stock camper wiring. Can also upgrade the wiring. Putting it outside in front of the wheel well also remains an option but is more work accommodating the connectors needed.