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Help/Critique of RV System, Wire/Connectors

When looking at a single solar charge controller versus three, you also have to take into account the cost of additional wiring, additional fusing (for 2s3p) and time to install. In my case, I simply didn't have room for a third solar charge controller.

3s2p is the least expensive and easiest way to install. It still has some coverage for shade.

Given the cost difference, if I had the room I would probably go with the three 100/30 and not carry a spare. Like you said, if one craps out you've lost only 1/3rd of your production. A quick install of a Y connector could remedy that. But I haven't run the numbers to see if 2s2p will fit a 100/30.
 
Voc 40.46V x 2s is just ok for 100v rating. There are rare atmosphere lense effects.
3s would give you 42A peak at 14v. So a 150v / 35A controller would be OK, you lose some power when it is easy to produce.
Two 3s strings shouldn't cost much more in wiring and you have redundancy with 2 controllers.
ss 150-35 and 150-45
I have the SS 100/50 and wish I bought 150v at least. 2 ea 48voc 250W panels, in parallel, on the ground often facing different directions.
I use the batteries OverKill solar BMS Bluetooth. It's quick and always ready. (download app from OverKill Solar web site)
In fact I almost never use the Smart Solar Bluetooth, or the Smart Shunt Bluetooth. The Smart stuff is constantly demanding updates that won't load from my Android phone, and blocks setting features. So I now use my old Android tablet and make sure its not WiFi to the internet.
 
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My OverKill Solar showed lower SOC vs. Victron Smart Shunt. So I change the OverKill Solar SOC settings to better match the charts here.

LiFePO4 Voltage Chart? thread​

 
Given the cost difference, if I had the room I would probably go with the three 100/30 and not carry a spare. Like you said, if one craps out you've lost only 1/3rd of your production. A quick install of a Y connector could remedy that. But I haven't run the numbers to see if 2s2p will fit a 100/30.
I think either three 2s strings or Pappion's dual 3s strings would be the way to go.
Voc 40.46V x 2s is just ok for 100v rating. There are rare atmosphere lense effects.
3s would give you 42A peak at 14v. So a 150v / 35A controller would be OK, you lose some power when it is easy to produce.
Two 3s strings shouldn't cost much more in wiring and you have redundancy with 2 controllers.
ss 150-35 and 150-45
I have the SS 100/50 and wish I bought 150v at least. 2 ea 48voc 250W panels, in parallel, on the ground often facing different directions.
I use the batteries OverKill solar BMS Bluetooth. It's quick and always ready. (download app from OverKill Solar web site)
In fact I almost never use the Smart Solar Bluetooth, or the Smart Shunt Bluetooth. The Smart stuff is constantly demanding updates that won't load from my Android phone, and blocks setting features. So I now use my old Android tablet and make sure its not WiFi to the internet.
I like this approach, and the 150-35 are still fairly affordable, could add a third 3s string if I use risers to mount above A/C (low profile unit).
 
Add'l questions re: alternator, chassis & house battery, and battery mode switch/solenoid:

We don't like camping in freezing temps, so I bought a LiFePO4 chassis battery; I will still add a battery warmer to make the system more robust. I found out LiFePO4 batteries can draw too much from the alternator, so I just ordered a Renogy DC-DC charger.

1. Renogy shows the DC-DC charger going from the chassis battery to the house battery, but I need this between the alternator and the chassis battery to avoid the chassis battery overloading the alternator, correct? I will never use the 100 Ah chassis battery to charge the 840 Ah house battery bank.

2. Our Winnebago has a battery bridging solenoid that bridges house and chassis batteries for boosting the starter, but it also bridges the chassis and house batteries when the engine is on, to charge both batteries. I don't want to use the alternator if there's good solar charging, so I was thinking of disconnecting the ignition wire to the solenoid so it does not automatically bridge the batteries when the engine is on. Then I could replace the battery boost momentary switch with a toggle switch for charging the house battery with the alternator?

3. I know the SmartShunt monitors the voltage for an accessory battery (such as a chassis battery), but voltage is not very useful for LiFePO4 batteries. For full monitoring of both house and chassis batteries, does anyone here use dual SmartShunts for true SOC monitoring of the chassis battery? The tricky part would be monitoring charging, correct? Should I cancel the Renogy and get a couple of Orion Tr Smart 12-12-30 DC-DC chargers instead? Or is this not really all that important?

Thanks in advance.

David
 
If you put the DC-DC charger anywhere in the circuit where the solenoid currently is then you will no longer be able to start the engine using the house LiFePO4 battery. The DC-DC charger is one-way. The DC-DC charger would need to be on its own circuit that is separate from the solenoid circuit.

The other issue is that your LiFePO4 battery (bank) may not have the amps to start an engine. I don't use my LiFePO4 batteries to start my on-board generator even though it's been shown to work by a couple of forum members.

My thought on shunts is that you would need two. The one for the starter battery would need to be a larger shunt than for the house battery since the engine starter pulls a buttload of amps. Probably more than the standard 500 amp shunt that comes with Victron BMV-712 can handle (for example).
 
If you put the DC-DC charger anywhere in the circuit where the solenoid currently is then you will no longer be able to start the engine using the house LiFePO4 battery. The DC-DC charger is one-way. The DC-DC charger would need to be on its own circuit that is separate from the solenoid circuit.
What if I put the DC-DC charger between the alternator and the chassis battery? (See updated diagram.) The down side is it limits the starter battery to charging at 60A. The upside is the battery solenoid should work normally to boost the battery. I just need to change the boost button to a switch with a blinking light and disconnect the ignition lead to the solenoid so it only bridges the batteries when the boost switch is on. On sunny drives I prefer solar charging to alternator charging.
The other issue is that your LiFePO4 battery (bank) may not have the amps to start an engine. I don't use my LiFePO4 batteries to start my on-board generator even though it's been shown to work by a couple of forum members.
I've heard this from an RV technician and several people on forums, yet a tiny lithium ion jump starter will start most engines. I found out the Sprinter's starter is 12V 2.3 kW, meaning 192A at 12V for 1-2 seconds. This sounds doable for most BMSes which have some surge capacity. But just to play it safe, I did get an AGM starter battery instead.

I've also heard much hand-wringing about LiFePO4 batteries drawing too much current and burning out alternators, and low voltage output, with most recommending 30-40 amp DC-DC chargers. But some things I've found:
1. The Sprinter alternator is rated at 220 amps, so it should comfortably handle at least 50%, if not 80%, of its rated amperage;
2. The Sprinter alternator puts out 14.2V at idle as well as up to 133 amps at idle when batteries are at a low SOC (https://windinmyface.com/Sprinter-Alternator-Primary.html)
3. The above blogger states it provides 60A charging current comfortably
4. The Sprinter's "smart" alternator changes output following demand; I would imagine a smart alternator wouldn't be very smart if it didn't limit output to avoid damaging itself.
 

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One of the main reasons to have the DC-DC charger is that it provides a LiFePO4-specific charge profile. If it was me, I would run the DC-DC charger on a separate circuit (in parallel with the solenoid circuit) between the starter battery and the LiFePO4 battery.
 
One of the main reasons to have the DC-DC charger is that it provides a LiFePO4-specific charge profile. If it was me, I would run the DC-DC charger on a separate circuit (in parallel with the solenoid circuit) between the starter battery and the LiFePO4 battery.
If you could upload a napkin sketch, that would be great. I'll try to noodle on it later tonight either way.

Thanks!
 
Disconnect the two lines coming out of the DC-DC charger from the chassis battery. Connect those two lines to your Lynx distribution box. Then make sure your solenoid is set so that it doesn't allow power to go to the LiFePO4 battery.
 
Disconnect the two lines coming out of the DC-DC charger from the chassis battery. Connect those two lines to your Lynx distribution box. Then make sure your solenoid is set so that it doesn't allow power to go to the LiFePO4 battery.
I'll look into doing that. Thanks!

Yesterday I got very little done except unpacked my battery cases and battery cells, which - after all the research and planning - is getting me very excited. Getting ready to top balance but I'm not sure my tester is up to the charging task (ZKE Tech EBD-A20H), but luckily the cells came charged to 3.27V, so shouldn't take too long.

I tried to return the 100 Ah LiFePO4 battery I bought for the chassis/starter battery and it says it's not eligible for return d/t flammable materials. But I looked at the Amazon listing and it says it's got CCA of 600 amps, which sounds like it should be fine with a 192A max Sprinter starter. Only downside would be the cold weather performance. Might be able to force the return issue if I test the capacity and it is less than 100 Ah.
 
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