Sun Trekker

[Campin]

Wiring coming together....

 

[Campin]

Making different length battery/inverter 2/0 cables.

 

[Campin]

More wiring...getting there.
Positive battery 2/0 cable run: battery-battery fuse-cutoff switch-shunt (monitor system performance)-relay (safety shutdown)-inverter-positive busbar.

Negative battery 2/0 cable run: battery-inverter-negative busbar-chassis ground.

 

[Campin]

Drilling positive, negative busbars.

 

[Campin]

Progress...

 

[Campin]

Solar system is (chassis) grounded. Luckily there’s an existing conduit (removed factory sealant) for 2/0 cable.

 

[Donlumber]

As I wire a question pops up...the ac neutral busbar in my RV is isolated (no ground bond) so this is a sub panel, correct? That means shore power is the main service.

I might be mistaken but I thought RVs were grounded to chassis?

 

[Campin]

I might be mistaken but I thought RVs were grounded to chassis?

Thnx Donlumber for the info! ...yes chassis grounded. I didn’t understand why AC neutral wasn’t grounded at the RV. Then I learned my RV panel is a sub panel, meaning neutral is bonded either at the inverter or shore power source.

 

[Campin]

Prep living in the wilderness, solar ready.

 

[Campin]

Yay! Off grid wiring complete, next prep and install lithium battery bank.

 

[Campin]

Next build a discharger to bottom balance the LiFePO4 cells. Discharger consists of four 50W/0.5 ohm power resistors mounted on a heat sink. I’ll reduce each cell voltage to 2.5V.

 

[Campin]

Bottom balancing a lithium cell, it works!

 

[Campin]

The latest, bottom balance my 24V battery. I built a discharger (power resistors and heat sink) to manage a non-BMS system.

 

[Campin]

Bottom balance cells for a 24V battery bank takes time (8 x 6 hrs). But the rewards are worth it! Reminds me of an old snickers commercial lol

 

[Campin]

Solar battery update: Things are looking sunny ; )
By discharging (kitty-corner) and passive balancing two (4 cell) banks, the difference between the banks is 1 mV, 2.570-2.571 (after numerous passes and discharge estimates). Next passive balance 8 cells overnight then discharge near 2.5V - bottom balance complete for my application...what a trip ?

 

[Campin]

After testing this battery bank (24V 280AH), it should meet impulse drive.

 

[Campin]

Bottom balance update: Passive balanced for 4 days, it seems 8 cells will settle around 2.632 volts (began at 2.585V). My hope is all cells will be near equal voltage at 90% SOC...in other words no rogue cells. The idea may be faulty but worth testing.

If tests are successful, the battery can pretty much manage itself and little monitoring.

 

[Campin]

Now that the 8 cells are (passive) balanced, they’re connected in series and charging. The target voltage is 26.60V (90% SOC). So far so good, cells look tight (no bulging).

 

[Campin]

Battery charge has stabilized around 90% SoC and cells aren’t bloated, that’s good.

 

[Ampster]

The target voltage is 26.60V

That is only 3.32 V per cell which is before the steep part of the curve. That is more like the resting voltage. But as you say they are bottom balanced so if you charge to that voltage you should have no issues. Are you going to use a BMS?