RV Solar Setup - Need Review

dpasch80

New Member
Joined
Sep 3, 2021
Messages
2
Hi All;

I am looking for some expert review before I build out my setup. Image below showing the wiring, the gauges, and the equipment. Its essentially Will's 400 watt setup with the addition of a AC/DC Charger. This setup would go in a compartment under the bed in the RV. The space I have to work with is 16" wide and 15" high by 40" long. Any feedback is welcome, especially if you see anything wrong with what is connecting where, wire gauges, or fuse sizes.

Also, in reading through the manuals and posts here I have a few specific questions.
  • In Will's book it says a 150A fuse between battery and inverter if the inverter is 1500W. However, the manual for the inverter suggests 250A fuse. Should that be upgraded?
  • I was assuming as this is lithium I do not need a battery monitor separate from what the charge controller says. However, in other posts those are included. Is that needed?
  • Is it okay to have solar charging the batteries at the same time as running the AC/DC converter?
  • I have not found anything direct that tells me the appropriate amp rating for the negative bus bar. I saw a larger 24V setup with a 250A bus bar. However, is a 150A sufficient? Or should bus bars be the same as the main fuse on the battery?
  • Lastly, I don't see much about grounding/bonding this to the chassis of the RV. Any tips on that?

Thanks for any and all help.
 

Attachments

  • solarsetup.png
    solarsetup.png
    91.2 KB · Views: 12

flynmoose

New Member
Joined
Jul 25, 2021
Messages
14
@dpasch80 - I'll preface my remarks with "I'm a newb too" so perhaps blind leading the blind but I think I can offer some qualified perspectives.
  • In Will's book it says a 150A fuse between battery and inverter if the inverter is 1500W. However, the manual for the inverter suggests 250A fuse. Should that be upgraded?
The fuse is to protect the wire - not the inverter. You show 2AWG going from battery to inverter. 2AWG has a "chassis wiring" (open cabling - easily able to reject heat - not in a wrap or conduit - most RV situations would be cabling) rating of 181A.

This is based on the table that can be found throughout the internet from Handbook of Electronic Tables and Formulas for American Wire Gauge (for example - https://www.powerstream.com/Wire_Size.htm). So if you use a 150A fuse, you will blow the fuse before exceeding the temp rating of the WIRE. And by staying below this ampacity rating you are also limiting your voltage drop in the wires.

So here is the catch. At 1500W you would pull 125A continuously (@12V nominal). So 150A fuse will be fine. But your inverter has a surge of 3000W - which is 250A. That is why the manufacturer is recommending 250A. So you don't blow the fuse if you spike the power. But 250A fuse would allow you to draw power until you melted that 2AWG wire in the case of a partial failure in the inverter or a chassis short.

The manual for your inverter does not state how long it could provide surge power of 3000W but given the price-point, I don't think it is long - probably on the order of 2sec or less. The surge is to allow a motor to startup.

If you get a Littelfuse 32V Slo Blo series fuse, they are have a current/timedelay curve. For the 150A fuse, you will get 4 seconds at 300A and 60 seconds at 200A. Your inverter will shut down for over power long before you exceed the fuse rating. BUT - if a partial short causes you to pull 160A - the FUSE will blow. It will just take more like 5min to blow. Plenty of time to protect from your wire catching on fire. (https://www.littelfuse.com/~/media/...bolt-down-fuses/littelfuse_mega_datasheet.pdf)

The alternative would be to size for the surge power - but that would be wasteful and expensive (you would have to go to 0 or 00 wire at 3000W...)

And now I'm going to caveat all the above by saying I just looked at the SOK battery. Both versions hava a max discharge rate of 100A (BMS limitation). So unless you are getting two batteries and putting them in parallel - you better not be looking to pull 1500W. The battery BMS will likely cut out on you.


  • Is it okay to have solar charging the batteries at the same time as running the AC/DC converter?
I haven't read Will's book. The SOK charge rating for both the 100AH and the 200AH battery is 50A. And again - newb! - but I think you have a risk of excessive current if your battery is low and both controller and converter decide to be in BULK charge mode. I think you could exceed the 50A charge current. But I could be wrong on that and the devices might be smart enough to sense voltage/current changes. But you should get someone more experienced her to confirm.

  • I was assuming as this is lithium I do not need a battery monitor separate from what the charge controller says. However, in other posts those are included. Is that needed?
If you mean a battery capacity measurement when you say "monitor" - I don't think the Renogy will tell you that very accurately. It will use resting battery voltage to calculate a state of charge. This doesn't work well with Lithium because the SOC / Voltage curve is VERY flat and very small voltage differences are hard to measure accurately. A shunt-based battery monitor actually measures the flow of power into and out of the battery (sort of like measuring water into and out of a bucket). These are much more accurate. If you don't want to spend $200 on a Victron, there are cheaper less featured options out there.

I have no qualified opinion on bus bar other than "bigger can't hurt." If space is a constraint - a 150A bus bar should be just fine if your fuse is 150A. But remember you are fusing the Inverter at 150A and then presumably you will have additional 12V loads. If you pull those before the inverter fuse, your negative bus could in theory carry more than 150A.

Good luck!
 

dpasch80

New Member
Joined
Sep 3, 2021
Messages
2
@flynmoose Thanks for the response, it helped several things click.

And now I'm going to caveat all the above by saying I just looked at the SOK battery. Both versions hava a max discharge rate of 100A (BMS limitation). So unless you are getting two batteries and putting them in parallel - you better not be looking to pull 1500W. The battery BMS will likely cut out on you.

Right, I oversized both the inverter in relation to the battery and the charge controller to the panels so that if I find that I need to expand either I don't need to buy new equipment at those points in the chain. Since I won't be running a microwave, AC or other hogs off the solar it should be light. When I did my energy audit I have about 500W if everything is on. Eventually I may tie the solar system into the RV DC system and make it my house battery as well but I don't really expect ever crossing 1000W from the DC system. So I suppose the 150A vs 250A fuse is moot at this point since the only way it could get to either is if something happened to the BMS.

If you mean a battery capacity measurement when you say "monitor" - I don't think the Renogy will tell you that very accurately. It will use resting battery voltage to calculate a state of charge. This doesn't work well with Lithium because the SOC / Voltage curve is VERY flat and very small voltage differences are hard to measure accurately. A shunt-based battery monitor actually measures the flow of power into and out of the battery (sort of like measuring water into and out of a bucket). These are much more accurate. If you don't want to spend $200 on a Victron, there are cheaper less featured options out there.

Ok, I will look into those. I had thought that the BMS would protect the battery (thus not needing a monitor for safety) and the charge controller would tell me the state of charge (thus not needing a monitor for information). But sounds like I still need it for information.

I haven't read Will's book. The SOK charge rating for both the 100AH and the 200AH battery is 50A. And again - newb! - but I think you have a risk of excessive current if your battery is low and both controller and converter decide to be in BULK charge mode. I think you could exceed the 50A charge current. But I could be wrong on that and the devices might be smart enough to sense voltage/current changes. But you should get someone more experienced her to confirm.

That makes sense. The AIMs charger does allow me to control how much that is sending so I could adjust for the solar if I were also charging - as my intent is to use the charger when solar is not giving me much juice. However, I wonder if anyone installs a switch between panels and controller in order to easily take solar out of the equation when charging via AC?

I have no qualified opinion on bus bar other than "bigger can't hurt."

I went and bought a 250A - as bigger can't hurt seems to be the general advice.
 
Top