Dear Dave,
I recently installed a battery monitoring system with a 500-amp shunt. It is a Trimetric TM2030 system from Bogart Engineering. I have a battery bank system comprised of four 240-amp lead acid batteries. I moved all my negative cables from the batteries to a 500-amp bus bar then ran a single cable from the bus bar to the negative terminal of my batteries, then another to the 500-amp shunt. Everything works as expected, except the rooftop air conditioner.
When the on-board Onan 4k generator is plugged into the transfer switch and is running, if i turn on the air conditioner it appears to run through the battery bank and my monitoring system instantly warns of a low battery state. I can see the percentage of charge drop rapidly.
If I turn off the invertor, which turns on automatically when the generator is plugged in, and then turn on the air conditioner, it appears to function as expected. There appears to be no drain on my batteries, but then my batteries don’t charge.
What am I missing here? Why would the air conditioner appear to run through the batteries? I thought the air conditioner was strictly wired as a 120v appliance. Any help with this conundrum would be appreciated. —Steven, 2010 Fleetwood Jamboree GT
Dear Steven,
This is an odd situation, as the roof air conditioner typically is wired directly to the 120-volt circuit breaker in the distribution center. It does have a 12-volt line going to the control module in the air conditioner as it powers the thermistor, which senses the temperature and other controls. However, this should not create the condition you are experiencing.
Air conditioner running through inverter?
As I often state, I’ve learned to never say never when it comes to RVs. What you are describing seems to have the air conditioner running through the inverter. Keystone started doing this two years ago with their SolarFlex setup. It has 600-800 watt solar panels and 400-600 Ah lithium batteries with a Victron MPPT and large inverter. They were showing this off at the Hershey RV Show and could run the roof air conditioner for about 2-3 hours, depending on the ambient temperature.
I doubt your 2010 Jamboree was wired this way from the factory and did not come with four 240 Ah batteries. So there have been some modifications, which could include the 120-volt power to the roof air conditioner going through the inverter. Most inverters have a pass-through feature that allows 120-volt power to pass through when plugged into shoreline power or when running the generator. When no 120-volt power is present, the inverter draws from the batteries to provide 120-volt power. This would show a major drain on the batteries, especially during initial start up, as it can spike to 40+ amps. That is why Keystone and anyone that is attempting to use house battery power to run the roof air conditioners will install a SoftStartRV product.
Don’t have automatic transfer switch
You stated: “When the on-board Onan 4k generator is plugged into the transfer switch….” That tells me you don’t have an automatic transfer switch, rather a “J” box like the photo below.
With this setup, the shoreline cord either plugs into the campground pedestal to get 120-volt power, or is physically plugged into this onboard outlet which is wired to the generator and gets 120-volt power when the generator is running. An automatic transfer switch (ATS) is an all-in-one box and automatically transfers or switches power to and from the generator line and shoreline to the distribution center.
Rig originally had a converter
Originally, your rig had a converter that is either part of the distribution center or standalone that receives 120-volt power and converts it to 12-volt to charge the house batteries. You indicated that turning off the inverter solves the air conditioner issue but you get no battery charging. So it appears another modification was adding a larger inverter that also is a battery charger and the old converter was disabled. Shutting off the inverter allows the 120-volt from the generator to pass through and run the roof air.
The confusing part is, if the air conditioner is supplied through the inverter, why does it not sense 120 volt and allow it to pass through? It could be an issue with the inverter. Has it always done this or just after installing the Battery Management System? Also, have you verified any of this with a multi-meter, and not just relied on the BMS? Also, does everything work when plugged into shoreline power?
Stay tuned, tomorrow we have an update and even more confusion!
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Some like it hot – But not your RV roof air conditioner!
Dear Dave,
We have always been able to run both air conditioners on our rig without issue until this summer. Texas has been extra warm. We had to replace both units but now our panel says shedding, and we can only use one unit at a time or they stop blowing cool air. We were thinking perhaps the refrigerator is pulling more amps due to the heat. How can we tell if there is a deeper issue? —Cynthia, Thor 2021 Four Winds Victory Series
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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Thank you, Dave! 🙂 Very interesting problem and helpful discussion around a potential answer. I am looking forward to reading the next installment! 🙂 Meanwhile, thanks again, have a great day, safe travels, and safe stays! 🙂
I would like to know what battery brand has a single 240 ah lead acid battery?
This is a classic case of “If it isn’t broken, don’t fix it.”
Interesting to see the final conclusion. Sounds like a fault in the inverter or something is taking the batteries to ground if they drain that quickly. Hmmm? Looking forward to more…… Thanks Dave.