critique my design?

jayhocking

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Okay, did a bunch of updates, switched as much as i could to 24v, and changed the hot water system, so it automatically comes on when the batteries are fully charged, but has an over ride switch for when I need it even if batteries aren't charged.

<<image removed, see post #23 below for corrected version>>
 
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Dzl

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Maybe I am misunderstanding (likely I am) but it looks as if the override switch, switches the water pump, not the heating element is that intentional?

Also, would you go into more detail about the design of the water heating system, I really like the concept, and would be curious to learn how you intend to implement it.
 

jayhocking

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Maybe I am misunderstanding (likely I am) but it looks as if the override switch, switches the water pump, not the heating element is that intentional?

Also, would you go into more detail about the design of the water heating system, I really like the concept, and would be curious to learn how you intend to implement it.
oops - applied my labels incorrectly :rolleyes: I'll delete that old image, and here's the corrected one. For the water heater setup, it's basically running the main power for the water heater through a relay, that's controlled by a 3-position switch.Option one is "bypass" and it's just the power coming from the fuse box - so when you have the switch in that position, the heater is just "on" and will use the battery bank, regardless of their charge state. The middle position will be "off" - and will be how you'd easily turn off the heater (you could also pull the fuse in the 24v fuse panel). The 3rd position is controlled by the internal rely in the Victron BMV712 monitor, which (from what I'm reading) can be setup via the bluetooth connection to trigger an external relay when certain conditions are met. In my case, I'll set it up so when the batteries are adequately charged (say 95%) it will switch on the water heater.

The water heater I'm planning on using is this one and I'm planning on using this submersible water heater element. Looks like others have already done this (although with the 12v 200w version of the element, not the 24v 600w one that I'm planning. The relay setup using the relay feature of the BMV712 is also something that's been done before, and I just cleaned up the drawing of the design a bit. Check out post #133 on this forum.

My 24-->12v buck converter is now oversized... I could use a much smaller one, but might leave it anyway. The price difference is not huge, and this gives me the option to charge my main truck battery off of my house system if I want to. Might be worth leaving it as-is.
Screen Shot 2021-11-01 at 10.38.29 PM.jpg
 

jayhocking

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Hey everyone, thanks again for the help. I've made some more progress - but could someone explain how I should connect the negatives to the chassis? I'm not planning on having any shore-power at all. And planning on running the negatives for each appliance/load all the way back to negative bus bar in the fuse boxes. But should the inverter be grounded to the chassis? The house batteries? the main (-) distribution block?
Screen Shot 2021-11-15 at 8.37.53 AM.jpg
 

jayhocking

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How will the battery packs balance properly? What is the mechanism? What happens when they drift out of ballance? If one goes to the top of the voltage range before the other it will shut off input current (not output) and this will slowly get worse won't it, thus loosing capacity and then you will eventually have to take it apart and manually ballance the packs. Am I missing something here?
I was under the impression (perhaps incorrectly) that the built-in BMS on these batteries would take care of that. I'm planning on these batteries - SOK 206AH - please let me know if you think I"m missing something here.
 

rmaddy

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could someone explain how I should connect the negatives to the chassis?
You don't connect the negatives to the chassis.

planning on running the negatives for each appliance/load all the way back to negative bus bar in the fuse boxes.
Perfect. This is much better than connecting the negatives to the chassis.

should the inverter be grounded to the chassis?
Based on many diagrams I have seen, including several from Victron, items like the inverter and the SCC that have separate case grounding terminals, wires should be run from those grounding terminals to the negative bus bar. Then you can run a wire from the negative bus bar to the chassis for a ground.

How will the battery packs balance properly?
I have those same two batteries in series in my system. Once they are properly balanced before connecting in series, they will stay balanced for a long time. I have setup midpoint voltage monitoring in my system (using the VE BMV-712). Based on this, my two batteries are still at the same voltage after about 8 months of use. If the time comes I can always take a day to rebalance them.

As long as you fully charge both before putting them in series you should be fine. check this video
Good video. It might be overkill but I would add two things. 1) If the two batteries have a large difference in initial SOC, I would charge them individually first. It's my understanding that hooking up two batteries with a big difference in SOC can cause a large current between the two batteries as they try to self balance. Once they are close you can connect them in parallel and continue with what is shown in the video. 2) After the parallel charge completes I would disconnect the charger but leave to the two batteries in parallel for at least a few hours. LiFePO4 voltage settles after a full charge. Keeping them in parallel can help ensure the settling is balanced.
 

jayhocking

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You don't connect the negatives to the chassis.


Perfect. This is much better than connecting the negatives to the chassis.


Based on many diagrams I have seen, including several from Victron, items like the inverter and the SCC that have separate case grounding terminals, wires should be run from those grounding terminals to the negative bus bar. Then you can run a wire from the negative bus bar to the chassis for a ground.


I have those same two batteries in series in my system. Once they are properly balanced before connecting in series, they will stay balanced for a long time. I have setup midpoint voltage monitoring in my system (using the VE BMV-712). Based on this, my two batteries are still at the same voltage after about 8 months of use. If the time comes I can always take a day to rebalance them.


Good video. It might be overkill but I would add two things. 1) If the two batteries have a large difference in initial SOC, I would charge them individually first. It's my understanding that hooking up two batteries with a big difference in SOC can cause a large current between the two batteries as they try to self balance. Once they are close you can connect them in parallel and continue with what is shown in the video. 2) After the parallel charge completes I would disconnect the charger but leave to the two batteries in parallel for at least a few hours. LiFePO4 voltage settles after a full charge. Keeping them in parallel can help ensure the settling is balanced.
Very helpful. thanks. So in my diagram, if I add a 1AWG cable from the (-) block to a good clean chassis ground, that should be fine, and it would be the only location that's grounded to the chassis, correct? All other negatives (or case grounding terminals) would just run into my (-) block.
 

rmaddy

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Very helpful. thanks. So in my diagram, if I add a 1AWG cable from the (-) block to a good clean chassis ground, that should be fine, and it would be the only location that's grounded to the chassis, correct? All other negatives (or case grounding terminals) would just run into my (-) block.
That's how I've seen it done in a few schematics and it is how I ended up doing it in my trailer camper.
 

HRTKD

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In my RV, I put in a ground bus bar. Those devices that specifically call for a ground to chassis and actually have a defined grounding terminal/fastener are connected to the ground bus bar.

None of the loads (lights, pump, etc) in my RV rely on a connection to the chassis. They all have two wires going to them. In other words, current isn't flowing through the chassis/frame.

This is all on the DC side. I haven't dug into the AC side much.
 

rmaddy

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In my RV, I put in a ground bus bar.
Presumably your bus bar is connected to the chassis, correct?

Is your ground bus bar wired to your negative bus bar so effectively the negative bus bar is grounded to the chassis as well?
 

Dzl

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Ground bus bar goes to the chassis. Negative bus bar does not.
I'm rusty on grounding logic in a vehicle, and its always been one of those topics that makes my head hurt, but I don't understand the logic of this (isolating negative from the vehicle chassis, but connecting safety grounds to the vehicle, in the event of a short to a chassis grounded component case, the current would not have a return path, or way to trip the OCP, right?
 

HRTKD

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I'm rusty on grounding logic in a vehicle, and its always been one of those topics that makes my head hurt, but I don't understand the logic of this (isolating negative from the vehicle chassis, but connecting safety grounds to the vehicle, in the event of a short to a chassis grounded component case, the current would not have a return path, or way to trip the OCP, right?

I'm no expert either. The existing RV wiring on the DC side likely has a line going from negative to chassis. The wiring from the factory is a huge mess and trying to follow cables is challenging. I just don't have a line running directly from my LiFePO4 battery or my common bus bars to the chassis.

As far as the overcurrent protection goes, aren't those independent of the chassis?
 

Dzl

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As far as the overcurrent protection goes, aren't those independent of the chassis?
Yes and no I think. OCP can be independent from the chassis (ground), but the safety grounding system is not independent from OCP. If there is a short to a chassis-grounded component case, but the chassis has no path back to the negative terminal, excessive current won't flow, and won't trip the OCP (which is one of the purposes of grounding as I understand it (provide a low resistance path and force a short/overcurrent condition, in a safer way than might occur otherwise)). So long as there is a connection somewhere in your system, this should be the case I think, but if there is no connection at any point between negative, and chassis-ground, I don't know what you will be getting the safety benefits of ground, because there could be a difference in potential between ground and negative. I'm quite rusty with all this, and also totally ignorant of how RV's/Trailers are wired from the factory, so if there are errors in my thinking please point them out.
 

time2roll

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As long as everything is run back to the bus I believe a single #8 bus to chassis frame is fine. If individual items such as the inverter have a chassis ground connection (separate from the negative power) that chassis ground should be connected to the vehicle frame close to the item. The manual will probably recommend #8 wire for this separate connection.
 
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