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Discussion Starter #1
Hey all,

I'm planning out the electrical for my 159" high roof build out. The design is still a work in progress but I have the diagram and components listed here:
https://docs.google.com/spreadsheets/d/18oFL4L0QFzfuz9Da03E2vTpY-qioxAagGYcr34jpGQI/edit?usp=sharing

The quick overview:

  • A single 275-325W solar panel going to an MPPT charge controller
  • 4 golf cart batteries wired in series-parallel
  • Either an ACR or a B2B charger for alternator charging
  • A 1500W or 2000W sine wave inverter hardwire to a few outlets
My plan for now is to get the DC portion of my build up and running and take a short trip in the van and iron out any bugs. Then come back a month later and install the inverter and 120v receptacles. I'll rough in the conduit for the 120V before I install my wall paneling so that I don't have to tear out my walls to add 120V.

My main questions right now are:

  • Should I ground my negative common to the vehicle chassis? Or connect my negative common to the vehicle battery negative... or both? My thoughts right now are to just run a 0 AWG wire to the vehicle battery.
  • With 4 (flooded lead acid) golf cart batteries, what should I be fusing my ACR to? 80A? I know the Promaster alternator puts out around 14.1V - 14.2V, but I'm not sure how high the charge current can get with 4 golf cart batteries in series-parallel.
How does this all look? I'm hoping for some feedback on my overall design and fuse sizes. Also, if you take a look through my spreadsheet I've included a voltage drop calculator --- you should be able to copy my spreadsheet and use the voltage drop calculator for your own planning.
 

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I always have to remind myself that wire gauge and length determine current capacity, and that the fuse just protects the wire. Depending on SOC (state of charge %), I've assumed our 500Ah AGM bank can take just about all the current our 220A alternator can normally produce. It's output is rated at 120A, which is also about the max anyone here has observed. So I sized the ACR (battery isolator) cable to handle 120A over it's 12ft length (2/0 AWG) and fused it at 120A. I carry extra fuses just in case the alternator gets over ambitious. As you said, you first need to determine how much current your FLA bank can accept, over the SOC range you anticipate. I believe AGM have a higher current acceptance than FLA, just not sure about the FLA details myself.

I assume your grounding question also relates to the ACR. The rest of your coach circuits only need to be grounded to the coach bank, which need not involve the chassis or starter battery. Some prefer to run a their ACR ground back to the starter battery itself. But it's also possible to use the chassis as the ground (return) path, as long as you can make a good reliable contact. I didn't want to run another 12ft of 2/0 back to the battery, so I coopted one of the floor tie-down bolts. I removed the paint at the contact point and also applied dielectric grease. If it ever fails, I know right where to look.
 

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Discussion Starter #3
Thanks for the info Steve. My rough assumption is that the charge current at a given SOC is roughly proportional to your amp-hour capacity. And with the higher internal resistance of the flooded lead acid compared to AGM I'm hoping I can get away with 80A for my 400AH battery bank.

I'd love to hear from anyone else who has run the same configuration of batteries as me about what charge current they're getting from the alternator, or what they're fusing the ACR at.

Yes, I'm referring specifically where to run the return path for the ACR to the house battery. I may sand some paint down to bare metal and try and test the resistance with a voltmeter. It seems that a lot of other folks here have had good results with just running the return path through the chassis.
 

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I wouldn't run the return path back to the starter as you should be able to ground to one of the tie down bolts.

As for fuse size, fuse at the starting battery (there is a slot for a MEGA fuse, use that) and at the relay for the size of wire you plan to run. If you're thinking 80 amps, I'd fuse to 100 amps and run 2 awg wire.
 

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There are "grounding studs" all over inside and outside of the van . Star washers and some dielectric grease will make good connections .
One less wire to mess with .
 

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I would make sure to put a shunt between the negative buss bar and the battery neg pole so that you can install a battery monitor like a Victron or Trimetric in to the system.
 

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Good call on the shunt. Any recommendations on a battery monitor?
I have the Bogart Trimetric RV2030. It's a solid piece but the display and overall appearance is dated. I'm OK with it but the Victron is definitely more modern and has some features the Bogart lacks like BT. If I had to do it again, I would by the Victron.
 

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I hesitate to comment on design because you have given no hint about what you plan to do with the electrical system. That is a lot of FLA power. Something like 430+- A-H at 12 volts! It might be you will need very little alternator charging, or a lot. Who knows?
 

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hi,
I have two golf cart batteries in series to make 12 volts -- 215 amp-hrs.


The most charging current I have seen is 38 amps and that only briefly -- so, probably fine with the 80 amp fuse. I would definitely not go lower. I am using 60 amps in that line for my two golf cart batteries (wire sized for 60 amps with small voltage drop).



You can use chassis grounds for the return paths to all the DC loads and to the van battery. I ran full size return wires for everything -- this was just for long term reliability. Ground connects to the chassis have to be very good, and even so, they can corrode over time and create electrical problems that are subtle. But, either scheme works. If you run return path wires, you still need to ground the neg terminal of the battery for safety reasons -- does not have to be a huge wire.
I would say that no matter what you do on other circuits, you do want a full size return on the run from the house battery to inverter -- the current is very large and just a little return (ground) path resistance is bad. Also good to place inverter as close to house battery as possible.



From your diagram, its hard to tell where you plan to put the van battery side fuse on the line from van battery to the ACR -- it should be as close to the van battery as possible, otherwise it does not protect the wire.


If you don't use an Inverter/Charger, then read up on where the AC side ground is tied to the neutral. When on shore power is back in the campground system when running off inverter, its inside the van. Inverter/Chargers do the shift automatically, but withe separate inverter and charger, you have to take of the switch over yourself via a transfer switch or the like. Its a safety issue, so you want to get it right.


Gary
 

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hi,

If you run return path wires, you still need to ground the neg terminal of the battery for safety reasons -- does not have to be a huge wire.

Gary
Hi Gary,

Could you expand a bit on the above?

I'm curious about the need to ground the neg terminal of the coach battery. Especially if it is a safety issue.
 

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Discussion Starter #12 (Edited)
Thanks for all the feedback, guys! I've gone ahead and bought a lot of the components, so it's time to start running wire and laying out the components.

RD, I'll comment on my intended usage to give you some more context. I'll be taking months-long trips in the van with my girlfriend. We'll mostly be boondocking and urban camping, with the occasional stay at campsites. There'll be a number of loads running on the electric system, including fridge, vent fan, lights, propane heater, water pump. But no heat loads: no microwaves, electric kettles, hairdryers, etc, and also only light AC loads, hence no need for a giant inverter.

With those goals in mind, I'm not building in a shore power hookup as we won't be able to use it most of the time. 400W of solar and 430 AH of flooded lead acid is for having a bit of autonomy out in the wild when we go hiking and climbing, and also just for the confidence that our fridge won't shut down and spoil all of our food. I'm going with an ACR instead of a battery-to-battery charger as many have recommended to me. My reasoning there is our solar and battery capacity is slightly oversized for our needs, and the alternator charge is more of a back-up than a main charging option. My guess is that typically I won't be drawing too much current from the alternator just because my SOC won't dip too far below 60-70% most of the time. (I'm hoping!)

Gary, thanks for the numbers. I'll start with an 80A fuse and keep a 100A on hand in case I draw more than that somehow. My diagram is not to scale geometrically, and I'll be placing the fuse as close to the battery as possible.

I'm planning on using one of these as a positive bus and also fuseholder(s): https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source.
My thinking is that this will keep all the fuses close to the battery bank and also keep things tidy and clean.


Edit: Another quick question. The BlueSea ACR has an ignition terminal that lets it isolate the house circuitry from the engine cranking. Is this necessary and how do I go about hooking it up to my starter solenoid?
 

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Your capacity is about 4 times the size needed for your listed use. You should rarely see a SOC under 85% or more. The solar should have you refilled with a hour of good sun. You might be able to go 5-6 days with no sun or alternator. Since you will be so well charged I’d suggest a simple solenoid for the interconnect and fit it with a switch to leave it disconnected most of the time. That way you use the solar controller to charge those batteries perfectly. See my $500 solar thread for the type of solenoid and wiring in my signature below. You will need a larger capacity one..... 150 amps?
 

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Discussion Starter #14
RD,
I don't mind having an oversized battery bank... It's only 130 extra pounds of lead, after all!


I forgot to mention, I'm considering adding an Isotherm SPA 15 to the system for hot water, which uses engine heat or a 750W heating element. I'll likely keep the Isotherm's heating element off most of the time, and just use it to keep the tank hot after the engine heats it up when I want to take a shower etc. (I'm not 100% committed to the Isotherm... Nervous about cutting through my coolant lines!)
 

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The Iso therm install was super easy. I had the factory "kit", but lots of people have used off the shelf connectors.

I ran my Isotherm off electric only for a few weeks before I tapped the engine lines. It took about 80Ah to raise the temp 60 degrees F in about an hour (I think). I use a bathroom timer switch to run the outlet for the Isotherm so there is no chance it can run down the batteries.
 

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That is good to know on the isotherm, I have one (slim 4 gallon square model) and was thinking of just leaving it off electric at first, but 80AH is too much on a consistent basis (and I have a 600 AH lithium battery bank!).

I am on a time crunch to complete my conversion and was thinking of saving a day of work by leaving it just electric for now, but that looks like a losing proposition.
 

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Hi Gary,

Could you expand a bit on the above?

I'm curious about the need to ground the neg terminal of the coach battery. Especially if it is a safety issue.

Hi,
Well, I'm not entirely sure. I've read a couple places that the house battery has to be grounded to the chassis for safety reasons, but in looking around, I've not seen a really good explanation.


But, if you don't ground neg terminal of house battery to chassis, then the chassis is floating, and if there is a short of a plus side wire to ground then the chassis will be at whatver the voltage of the hot wire is. If the house battery is grounded, then as soon as you get the short of a hot wire to chassis, it will conduct heavily and blow a fuse (which is good).


Not sure that's the complete explanation -- maybe someone else knows?


Gary
 

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Seems logical, Gary, although it seems odd it gets so little attention. Of course, the ground/return on your battery isolator circuit covers both bases. But in that case, the ground cable should be "huge", generally the same gauge as the isolator's positive cable.
 

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Thanks, Gary for getting back to me. My ears perk up when it comes to safety issues and so I wanted more information. And Steve is right, it never gets mentioned.
 

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No Ground / No Alernator charge.

Good Morning. We built our entire system without a chassis ground. The last thing we installed was the Stinger battery isolator. We found that we got no charging at the battery from the alternator until we put a jumper from bus bar to chassis. Shut solar off for this test. Note the control circuit for teh stinger has a ground, but without that temporary jumper bus to chassis, we got nothing from the alternator. We are installing a permanent chassis ground.
 
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