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Old 05-20-2020, 07:54 PM   #1
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Question Newbie on Batteries and Inverter S/U. HELP!

We want to do more dry camping, so I started looking at what it upgrade/add a simple solar/inverter/battery system. I did an audit and figured we would use ~ 550W per day (~45ah)

We have a 32" Sprinter 5er and had to first upgrade the battery to an 12V AGM 100ah (I understand most use (2) 6V in series. The recessed cavity was for (1) Group27 battery). To keep it charged while dry camping I have a small Renogy 100W portable solar panel with a 20 PWM (In know an MPPT would have been better).

I also wanted to add a small inverter and worked with some folks on a different forum who said a 700W Inverter would be all I needed.

Now I have a few questions, I was hoping someone could help me with.

1) If I was to add a second 12V AGM 100ah battery and connect in parallel, (for an additional 100ah) see photos. I would have to either locate it 3ft away or turn on its side to locate it next to the existing battery storage box (recessed in the front compartment). ??? Any advise?

2) If I can locate the second battery 3ft to the left, it would give me room to mount the 700W Inverter, Fuse Block, SCC, Shunt for BMS, and Terminal Block (not all components are shown).

3) All of the cables coming from the Stock Charger/Converter to (2) 50 AMP Auto Reset Circuit Breakers and a battery disconnect switch, are all 6AWG wire. Should I continue to use the 6AWG for the newer components or increase the wire gauge?

Thank you in advance. I hope you are all safe and well. Crazy times.
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Old 05-20-2020, 08:09 PM   #2
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Old 05-20-2020, 09:21 PM   #3
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I think you need the size the pair of cables used to interconnect the two batteries in parallel to the size required to sustain your inverter.

The cable size needs to account for the DC current and length of the cables. I would recommend installing a BMV-712 with shunt while you are doing the wiring. The BMV-712 will help you monitor the amps going into and out of your batteries and track the state of charge.
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Old 05-25-2020, 12:10 AM   #4
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I gather you now have a matched pair of AGMs (I see an FLA in the first photo, but it's now gone?). To keep charging and discharging of the two parallel batteries even for longest battery life, you will want first jumpers that parallel the two batteries, then connect the charger and inverter to the negative terminal of one battery and the positive terminal of the other battery. If this isn't clear, let me know.

As for wire size, the inverter will draw something over 60 amps from the batteries if you fully load the inverter when the batteries are down around half state of charge (about 12.1V). #6 copper will handle that thermally. #6 is about 0.0004 ohms per foot. So voltage drop will be about 0.028 volts per foot. Assuming about 8 feet round trip, that's a voltage drop of about 0.22 volts in the wire to the inverter. Bump that up a bit for voltage drop in the wire between the two batteries. Bump it up a bit more to cover voltage drop in any circuit breakers and fuses. So up around 0.4V total. Maybe 0.5V. Starting with batteries at 12.1V (50% charge), that's down around 11.6V at the inverter. Most inverters will shut down if voltage drops down in the mid 11's so this is a bit marginal.

You can't do much about fuses/circuit breakers but going to #4 wire at about 0.00025 ohms per foot would reduce the wire part of the voltage drop by 40% or a bit over 0.1V. #2 would get you down to 0.000156 ohms/ft and shave off another 0.05V (very roughly). Doubling up the #6 would be between these two.

If my guestimate of 8' of round trip wire to the inverter is high, shorter wire will help you get away with #6.

If you won't actually ever use the full 700W or will use it only when the batteries are above 75% charge, you should be okay with #6 (even at 8'). If not, larger wire would be a good idea.

Or, if you are comfortable working with the #6 and would prefer avoiding the hassle of larger wire, you could parallel each section of #6 with a second #6. Heck, you could give the single #6 a try and see if you can get away with it. if the inverter kicks off on high load with the batteries down around 50% SOC, you could then add a second #6.
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Old 05-25-2020, 07:42 AM   #5
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Quote:
Originally Posted by astrocamper View Post
I think you need the size the pair of cables used to interconnect the two batteries in parallel to the size required to sustain your inverter.

The cable size needs to account for the DC current and length of the cables. I would recommend installing a BMV-712 with shunt while you are doing the wiring. The BMV-712 will help you monitor the amps going into and out of your batteries and track the state of charge.
Thank you Jeff....I have a BMS (not the Victron)...and I bought some 2 AWG cable for the battery to inverter. Its about 5ft from the inverter to the battery bank, to reduce voltage drop. Now for "fuses". I hav etc do some math here. Also some people use individual fuses and others use a 12V fuse distribution block, I guess the latter gives you more options for connecting other 12V appliance. Thank you- I appreciate your help.
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Old 05-25-2020, 08:17 AM   #6
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Originally Posted by hclarkx View Post
I gather you now have a matched pair of AGMs (I see an FLA in the first photo, but it's now gone?). To keep charging and discharging of the two parallel batteries even for longest battery life, you will want first jumpers that parallel the two batteries, then connect the charger and inverter to the negative terminal of one battery and the positive terminal of the other battery. If this isn't clear, let me know.

As for wire size, the inverter will draw something over 60 amps from the batteries if you fully load the inverter when the batteries are down around half state of charge (about 12.1V). #6 copper will handle that thermally. #6 is about 0.0004 ohms per foot. So voltage drop will be about 0.028 volts per foot. Assuming about 8 feet round trip, that's a voltage drop of about 0.22 volts in the wire to the inverter. Bump that up a bit for voltage drop in the wire between the two batteries. Bump it up a bit more to cover voltage drop in any circuit breakers and fuses. So up around 0.4V total. Maybe 0.5V. Starting with batteries at 12.1V (50% charge), that's down around 11.6V at the inverter. Most inverters will shut down if voltage drops down in the mid 11's so this is a bit marginal.

You can't do much about fuses/circuit breakers but going to #4 wire at about 0.00025 ohms per foot would reduce the wire part of the voltage drop by 40% or a bit over 0.1V. #2 would get you down to 0.000156 ohms/ft and shave off another 0.05V (very roughly). Doubling up the #6 would be between these two.

If my guestimate of 8' of round trip wire to the inverter is high, shorter wire will help you get away with #6.

If you won't actually ever use the full 700W or will use it only when the batteries are above 75% charge, you should be okay with #6 (even at 8'). If not, larger wire would be a good idea.

Or, if you are comfortable working with the #6 and would prefer avoiding the hassle of larger wire, you could parallel each section of #6 with a second #6. Heck, you could give the single #6 a try and see if you can get away with it. if the inverter kicks off on high load with the batteries down around 50% SOC, you could then add a second #6.
Hi hclarkx....yes. the first photo was the original battery set up. The person I bought the 5er from had a 12V 660CCA Marine Battery installed (they never did any dry camping). So I now have the 2 AGM-100ah batteries for a parallel set up.
I bought 6ft of 2 AWG cable with lugs to use from the inverter to the batteries and 12" of 4 AWG with lugs for jumpers on the batteries. I also have a BMS with a 100A shunt to connect.

I have enough 2 AWG cable to make my parallel battery jumpers (although more work) if you think that would be better? Or just use the 4 AWG jumpers.

Do you recommend individual fuses to busbars between inverter and solar charger do you like the 12V fuse distribution block option?
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Old 05-25-2020, 08:26 AM   #7
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Forgot to mention I relocated the inverter back to the right and I am thinking of mounting it on the ceiling (above). This allows me to run the Inverter Switch up through the bulkhead and into the main cabin of the 5er. But the main reason was to give it more room away from the batteries (which are in a tight enclosed area.

Also what do your think about the (2) 50A thermal breakers Keystone has installed...should I replace them with a more apt to date fuses?
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Old 05-25-2020, 01:23 PM   #8
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this is a hack of this thread but i have a question regarding the photo in post #1. the existing battery seems to be sitting in a battery box very similar to the one we have. we have a group 27 battery and the battery box is sized for it. there is a top piece that screws on to encase the battery and the top piece is vented. i am contemplating changing to either group 31 or GC2 batteries but they would need new battery boxes sized to them. does any body know who makes / stocks these battery boxes?
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Old 05-25-2020, 02:09 PM   #9
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this is a hack of this thread but i have a question regarding the photo in post #1. the existing battery seems to be sitting in a battery box very similar to the one we have. we have a group 27 battery and the battery box is sized for it. there is a top piece that screws on to encase the battery and the top piece is vented. i am contemplating changing to either group 31 or GC2 batteries but they would need new battery boxes sized to them. does any body know who makes / stocks these battery boxes?
Yes it is. That is why I choose this battery (at least one can fit) Group 27 fits perfect. If you are staying with the "lead acid" unsealed battery, then a "vented box" would be needed. The reason they used these battery boxes was to vent thru an exhaust tube, any released fumes that could be dangerous. On elf the advantages of a sealed AGM or Lithium Battery is you do not have that issue. If you do want to enclose the batteries and you have the space..do a Google search and you will find ALL kinds of examples of boxes (enclosures) which can be modified (i.e. cable entry/exist holes etc).
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Old 05-26-2020, 01:40 PM   #10
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Hi hclarkx....yes. the first photo was the original battery set up. The person I bought the 5er from had a 12V 660CCA Marine Battery installed (they never did any dry camping). So I now have the 2 AGM-100ah batteries for a parallel set up.
I bought 6ft of 2 AWG cable with lugs to use from the inverter to the batteries and 12" of 4 AWG with lugs for jumpers on the batteries. I also have a BMS with a 100A shunt to connect.

I have enough 2 AWG cable to make my parallel battery jumpers (although more work) if you think that would be better? Or just use the 4 AWG jumpers.

Do you recommend individual fuses to busbars between inverter and solar charger do you like the 12V fuse distribution block option?
First an addendum to my earlier post based on something Astro noted. Those jumpers will carry half the inverter current so can be sized appropriately. That means about half the size of the main leads to the inverter.

But, you apparently knew this since you went #4 on the jumpers and #2 to the inverter. #4 is good for about 100 amps so would support a 200 amp inverter. That's about a 2.4 kW inverter. The #2 is also just fine. And your lengths easily rule out a voltage drop problem. In fact, you are set for a larger inverter.

I didn't use any fuses in my system. I've read here that fuses have lower resistance than a circuit breaker but have not confirmed that. The difference can't be much. And that was not an issue for me because I use LFP and have plenty of voltage to play with. It's not really an issue for you either because AGM batteries don't let voltage drop nearly as much as FLA under heavy load. And, in your case with short leads, you won't have a voltage problem. The main reason I used circuit breakers is because they provide a disconnect wherever they are. You want to be able to isolate each device when you are working on it or testing it or for storage. And a solar controller needs a disconnect on the 12V side (actually both sides but the focus here is at 12V). Proper solar controller start-up is to energize from the battery, let it boot up, then connect the solar panels. That requires the 12V disconnect which might as well be a circuit breaker.

My system has a 150 amp circuit breaker between the inverter and the battery. On the inverter side of that breaker I feed other devices. As such, that breaker acts as a "main" disconnect/breaker and also is the breaker that protects the inverter and its wiring. I have smaller breakers (all 20 amp iirc) serving the original trailer load and the solar controllers. These are fed by jumpers to the inverter terminal (I would have preferred jumping to the load side of the main breaker but the terminal there was not tall enough).

The breakers are the cheap in-line ones each jumpered to the large inverter terminal. That inverter terminal is my "bus bar". I don't like seeing true busbars with lots of copper exposed. Just invites a short-circuit. You definitely want everything well insulated between the battery and your first or main circuit breaker. That is unprotected with your batteries. With LFP drop-in, the BMS protects that wire in my system.

I've probably seen photos of the 12V distribution block but don't recall. If it provides individual circuit breakers and is well insulated, it might be a good solution.

BTW, I'm sure it's clear I'm talking about circuit breakers with a "handle," not the self-resetting or push-button type. I.e. like this or this ....

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

RV fires are not uncommon, so the protection is important.
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Old 05-26-2020, 05:35 PM   #11
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My bus bars have a protected cover. I keep the opening facing down so nothing will fall into the open area to short.

I connected each of my 100 amp-hour LiFePO4 batteries to a post using 2/0 cables and used a 4/0 cable to connect to the shunt and disconnect+fuse before attaching to a 2nd pair of bus bars. My inverter connected to the 2nd set of bus bars along with other devices like my MPPT controllers.

I like the bus bars because I don't have to stack so many cables onto a post.
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Old 05-27-2020, 04:44 PM   #12
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My bus bars have a protected cover. I keep the opening facing down so nothing will fall into the open area to short.

I connected each of my 100 amp-hour LiFePO4 batteries to a post using 2/0 cables and used a 4/0 cable to connect to the shunt and disconnect+fuse before attaching to a 2nd pair of bus bars. My inverter connected to the 2nd set of bus bars along with other devices like my MPPT controllers.

I like the bus bars because I don't have to stack so many cables onto a post.
Excellent. I'd not seen these before. I envision a 150A breaker (+/-) feeding this busbar and a row of these (link below) or similar under it. Keep the wires from the busbar to the circuit breakers short and not too small because that section of wire is not well protected. I.e., the upstream breaker (or fuse) might be 150 amp and the wire leaving the busbar just #10 and only good for 30 or 40 amp (continuous). Theoretically that 150 amp breaker could allow that #10 to melt from a sustained 75 amps. In reality though, the breaker at the end of a few inches of #10 will open at, say, 20 amps, and protect the #10 from overload. That leaves short-circuit protection. If a short occurs at the end of the #10 (ahead of the 20 amp breaker), the current will be hugely above 150 amps and will open the "main" breaker before the #10 can melt. To be honest, I have as much as 2 feet of wire between my "busbar" (post) and the circuit breaker. Not ideal, but as noted above, it would be hard to have a problem that is not covered (even a couple of feet of #10 will result in hundreds of amps for the time needed to get the "main" breaker open). I'd hesitate to use anything smaller that is not properly protected by a circuit breaker or fuse between it and the battery (you don't want a #14 wire acting like a fuse).

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

This is my setup. The wires are a bit neater now and all black and marked but this gives you the idea.

View more in SlickPic photo gallery
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Old 06-01-2020, 06:23 PM   #13
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Excellent. I'd not seen these before. I envision a 150A breaker (+/-) feeding this busbar and a row of these (link below) or similar under it. Keep the wires from the busbar to the circuit breakers short and not too small because that section of wire is not well protected. I.e., the upstream breaker (or fuse) might be 150 amp and the wire leaving the busbar just #10 and only good for 30 or 40 amp (continuous). Theoretically that 150 amp breaker could allow that #10 to melt from a sustained 75 amps. In reality though, the breaker at the end of a few inches of #10 will open at, say, 20 amps, and protect the #10 from overload. That leaves short-circuit protection. If a short occurs at the end of the #10 (ahead of the 20 amp breaker), the current will be hugely above 150 amps and will open the "main" breaker before the #10 can melt. To be honest, I have as much as 2 feet of wire between my "busbar" (post) and the circuit breaker. Not ideal, but as noted above, it would be hard to have a problem that is not covered (even a couple of feet of #10 will result in hundreds of amps for the time needed to get the "main" breaker open). I'd hesitate to use anything smaller that is not properly protected by a circuit breaker or fuse between it and the battery (you don't want a #14 wire acting like a fuse).

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

This is my setup. The wires are a bit neater now and all black and marked but this gives you the idea.

View more in SlickPic photo gallery
Very Nice. I wish I had that much room. I know fuses are important to protect the wire and the devices. I ordered these (Will Prowse used these) I hope these are OK. I have two order everything online..hardware stores do not carry these types of parts.

https://www.amazon.com/WindyNation-F.../dp/B079ZJY92Z
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Old 06-01-2020, 06:44 PM   #14
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Excellent. I'd not seen these before. I envision a 150A breaker (+/-) feeding this busbar and a row of these (link below) or similar under it. Keep the wires from the busbar to the circuit breakers short and not too small because that section of wire is not well protected. I.e., the upstream breaker (or fuse) might be 150 amp and the wire leaving the busbar just #10 and only good for 30 or 40 amp (continuous). Theoretically that 150 amp breaker could allow that #10 to melt from a sustained 75 amps. In reality though, the breaker at the end of a few inches of #10 will open at, say, 20 amps, and protect the #10 from overload. That leaves short-circuit protection. If a short occurs at the end of the #10 (ahead of the 20 amp breaker), the current will be hugely above 150 amps and will open the "main" breaker before the #10 can melt. To be honest, I have as much as 2 feet of wire between my "busbar" (post) and the circuit breaker. Not ideal, but as noted above, it would be hard to have a problem that is not covered (even a couple of feet of #10 will result in hundreds of amps for the time needed to get the "main" breaker open). I'd hesitate to use anything smaller that is not properly protected by a circuit breaker or fuse between it and the battery (you don't want a #14 wire acting like a fuse).

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

This is my setup. The wires are a bit neater now and all black and marked but this gives you the idea.

View more in SlickPic photo gallery
Very Nice. I wish I had that much room. I know fuses are important to protect the wire and the devices. I ordered these (Will Prowse used these) I hope these are OK. I have two order everything online..hardware stores do not carry these types of parts.

https://www.amazon.com/WindyNation-F.../dp/B079ZJY92Z
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