Charging Trailer Batteries with VAN Solar System

[Huck]

Let me ask a different way leaving the refrigerator out of it.

I have 600w of solar panels, 2 100ah lithium batteries, and an inverter in my van isolated from the van's electrical system.

In my trailer I have 2 100w solar panels and usable 70 ah batteries.

I would like a quick connect/disconnect of the van's power either through the batteries or inverter to the trailer's electrical system or battery. It has to be simply so that I can just unplug and drive the van away and plug back in when I return.

Ideally, this should allow me to run everything in the trailer, at least during daylight, including ac and microwave. The draw from the ac is about 5a at 110v so about 50 ah.

[ThomasC]

Originally Posted by John in Michigan

In 12v mode the fridge is using 10 amps of current. I suppose you could try using the tow vehicle lithium batteries via the inverter to charge the trailer batteries at a 10 amp rate or higher.

I think the frig uses more watts in either AC or DC than you are counting on. From what I can gather you need around 3-400 watts with an electric heater whether it is AC or DC.

I have been running my frig while traveling from a DC to DC charger to my batteries to my inverter to the frig. I have a 2-way fridge. More information here.

https://www.fiberglassrv.com/forums/...d-92081-2.html

[gordon2]

Originally Posted by Huck

...
Ideally, this should allow me to run everything in the trailer, at least during daylight, including ac and microwave. The draw from the ac is about 5a at 110v so about 50 ah.

ah (amp hours, usually Ah) is a measure of the total current over a period of time. So you need to define the time period if you want to report the amp hours.

Now 5 amps at 110 / 120 Volts AC is 550-600 watts. Few air conditioners use so little power so I have to question that. Most RV A/Cs would be 12 amps or more, and require a circuit of 15 or 20 amp capacity (don't forget about startup surge current). So you are looking at 1500 watts to even think about running those A/C units, and 2400 might be better. What A/C do you have? And Microwave ovens range from 700 to 1200 watts give or take. What microwave do you have? And most important... What inverter do you have? Most of what you are asking depends on the answer to that question.

As for using the 30 amp shore power cord.. I see no reason you could not connect it to the inverter. A 15 to 30 adapter would not doubt be needed, and you would need to budget your power as to not overload the system. But it seems like a reasonable idea. I just hate to see the power loss when you use 12 volts DC to power an inverter to power a 120 VAC charger or power supply to run a 12 VDC appliance. (But Rube Goldberg would like it )

[Huck]

Originally Posted by gordon2

Now 5 amps at 110 / 120 Volts AC is 550-600 watts. Few air conditioners use so little power so I have to question that. Most RV A/Cs would be 12 amps or more, and require a circuit of 15 or 20 amp capacity (don't forget about startup surge current). So you are looking at 1500 watts to even think about running those A/C units, and 2400 might be better. What A/C do you have?

A 5000 btu AC uses a little under 5 amps.

As for using the 30 amp shore power cord.. I see no reason you could not connect it to the inverter. A 15 to 30 adapter would not doubt be needed, and you would need to budget your power as to not overload the system. But it seems like a reasonable idea. I just hate to see the power loss when you use 12 volts DC to power an inverter to power a 120 VAC charger or power supply to run a 12 VDC appliance. (But Rube Goldberg would like it )

I think I have enough power that the inefficiency won't be a problem. The 12v appliances will run off the batteries which are being charged by the 2 100w solar panels until the batteries need to be charged from the van system.

I already have a refrigerator in the van that draws less than 5 amps at 12v. I was going to run that one as a freezer and the one in the trailer as a refrigerator. I don't know if a chest refrigerator will fit in the space in the trailer, or I would just replace it.

[John in Michigan]

Huck, keep in mind that in the example you mentioned above, while the 5 amp (at 110vac) air conditioner running for 10 hours during the day is consuming 50 amp hours at 110vac while running continuously during that period, but that needs to be converted to power consumption at 12 vdc. So the air conditioner is consuming 5500 watt hours per day, but the 90% efficient inverter has to provide 6111 watt hours per day or 509 amp hours (at 12vdc) per day to run that air conditioner.

[Huck]

Originally Posted by John in Michigan

Huck, keep in mind that in the example you mentioned above, while the 5 amp (at 110vac) air conditioner running for 10 hours during the day is consuming 50 amp hours at 110vac while running continuously during that period, but that needs to be converted to power consumption at 12 vdc. So the air conditioner is consuming 5500 watt hours per day, but the 90% efficient inverter has to provide 6111 watt hours per day or 509 amp hours (at 12vdc) per day to run that air conditioner.

Which means in the summer, I could run it some in the afternoon and maybe 3-4 hours at night. What I really hope for is just to be able to cool down the trailer in the evening or if I need to be inside during the day. This would primarily be for beach camping where there is no shade anywhere.

I bought a Clam tent thinking that would provide shade and a cooler spot, but the tent heats up like an oven in the summer. I have been doing experiments on trying to keep it from getting so hot and the best I have been able to do is keep it a little above the outside temperature. I was able to do that by draping a reflective tarp over the tent in such a way that there was a little pocket of shade on the East and South sides. By opening the windows where those shade pockets are, I could get a little cooler air into the tent. I also have a box fan pushing air from the North-West side into the tent. It is actually not too bad inside the tent, even though the temp gets up to near 100 degrees. At least it is shaded and the air is moving.

[gordon2]

Originally Posted by Huck

A 5000 btu AC uses a little under 5 amps...

OK, now we are getting some specific information and now I can stop assuming its a typical roof type RV air conditioner. But we still don't know anything about your inverter and need to continue to assume... so lets assume its 1500 watts or more. Then go ahead and connect the shore power to the inverter. See if it can handle the A/C. If it can then next step is to figure how long you can run the A/C and whatever else you want to run from the van's secondary battery bank.

So another question... do you have a battery bank monitor like a Victron or Trimeteric brand? For the van, camper or both?

[John in Michigan]

Also look into installing a 12vdc air conditioner (roof top or mini split). It would use somewhat less power and no inverter power loss. There are threads on this forum covering this topic. Here are some roof top 12vdc air conditioners:

https://happiercamper.tumblr.com/post/142336540366

https://www.vanlifeoutfitters.com/st...r-conditioner/

https://www.vanlifeoutfitters.com/ca...ners-for-vans/

[Huck]

Originally Posted by gordon2

OK, now we are getting some specific information and now I can stop assuming its a typical roof type RV air conditioner. But we still don't know anything about your inverter and need to continue to assume... so lets assume its 1500 watts or more. Then go ahead and connect the shore power to the inverter. See if it can handle the A/C. If it can then next step is to figure how long you can run the A/C and whatever else you want to run from the van's secondary battery bank.

So another question... do you have a battery bank monitor like a Victron or Trimeteric brand? For the van, camper or both?

Just the van - Victron.

AIMS Power DC to AC Pure Sine Power Inverter (2000 W)

Van Solar Diagram

[CarlD]

Huck, You can certainly plug your trailer into the inverter in your TV to run your fridge. It will also charge your trailer batteries if needed. If you want to run an AC you need to make sure the TV inverter has sufficient capacity to run your desired loads (battery charging, fridge, AC, etc). Just try it and see what happens. The inverter overload circuit may turn off the inverter or a circuit breaker may trip, but that's what their there for.

The efficiency issue will only reduce the capacity of the TV batteries. If that is a problem perhaps you could add another battery. A simple solution is available now, an optimized solution is possible if you want to spend more money.

[CarlD]

Originally Posted by John in Michigan

Also look into installing a 12vdc air conditioner (roof top or mini split). It would use somewhat less power and no inverter power loss. There are threads on this forum covering this topic. Here are some roof top 12vdc air conditioners:

https://happiercamper.tumblr.com/post/142336540366

https://www.vanlifeoutfitters.com/st...r-conditioner/

https://www.vanlifeoutfitters.com/ca...ners-for-vans/

$2700!!!!! for a Dometic Coolair. Somebody is making some serious money!!!

[Huck]

Just did a test with the trailer's electrical cable plugged into the van's inverter.


The A/C runs fine.
The microwave runs fine.

But now I do have a question. If I run the A/C and microwave at the same time, I lose power for several seconds, but then it comes back on. I believe the circuits in the trailer require a manual reset, so it must be some component in the van that is automatically resetting. The diagram is in my previous post.

[gordon2]

Originally Posted by Huck

Just did a test with the trailer's electrical cable plugged into the van's inverter.


The A/C runs fine.
The microwave runs fine.

But now I do have a question. If I run the A/C and microwave at the same time, I lose power for several seconds, but then it comes back on. I believe the circuits in the trailer require a manual reset, so it must be some component in the van that is automatically resetting. The diagram is in my previous post.

A/C AND microwave is a lot of power.. I have no doubt it overloads the inverter or some other part of the system. In fact it probably exceeded the 15 amp limit of the 30-15 adapter (it might get hot and even melt). Get the wattage of all the 120 VAC stuff in your camper, add the sum of what you want to run at the same time, check that the inverter is rated to supply that continuously. Dont exceed the rating of any of the components in the chain (extension cord, etc).

EX: Your A/C is likely about 600 watts. The smaller microwaves are about 700. Most are more like 1200. If your converter is also on, add that too. It will use more power when charging the battery. Maybe you can shut it off (at the breaker). So A/C, standard size microwave, and converter in charge mode could easily be > 2000 watts.

Frankly I would resist running anything else when the A/C is on. You can turn it off for the few minutes it takes to microwave a meal. You need to have an energy budget.

[Huck]

Just did a test with the trailer's electrical cable plugged into the van's inverter.

The A/C runs fine.
The microwave runs fine.

But now I do have a question. If I run the A/C and microwave at the same time, I lose power for several seconds, but then it comes back on. I believe the circuits in the trailer require a manual reset, so it must be some component in the van that is automatically resetting. The diagram is in my previous post.

I assume it's the 150a breaker between the positive busbar and the inverter. The initial surge from the microwave must push the surge output over 3000 watts when the ac is running.

[John in Michigan]

Look at the spec plates for the microwave and for the air conditioner. Whatever advertised microwave power is, e.g., 700 watts or 1000 watts, that is typically the output. You need to determine the microwave INPUT wattage and/or amperage, which is typically 50% higher than the output! For the air conditioner, there will be an initial power surge. Again, check read the specs for these devices.

[Huck]

Originally Posted by gordon2

A/C AND microwave is a lot of power.. I have no doubt it overloads the inverter or some other part of the system. In fact it probably exceeded the 15 amp limit of the 30-15 adapter (it might get hot and even melt). Get the wattage of all the 120 VAC stuff in your camper, add the sum of what you want to run at the same time, check that the inverter is rated to supply that continuously. Dont exceed the rating of any of the components in the chain (extension cord, etc).

EX: Your A/C is likely about 600 watts. The smaller microwaves are about 700. Most are more like 1200. If your converter is also on, add that too. It will use more power when charging the battery. Maybe you can shut it off (at the breaker). So A/C, standard size microwave, and converter in charge mode could easily be > 2000 watts.

Frankly I would resist running anything else when the A/C is on. You can turn it off for the few minutes it takes to microwave a meal. You need to have an energy budget.

I believe the inverter has a surge rating of 3000 watts. It was the surge from the microwave plus running the AC that caused the problem. The inverter seems to handle the surge from either stand alone, but not adding one on top of the other. The surge from microwave is about 2500 watts and the ac was using about 600 watts, so it went a little over 3000 watts. That's not a problem, as now I know to turn off the ac if I need to use the microwave. I was just surprised that the system automatically reset itself. That's potentially a problem as it could keep failing, resetting, failing, resetting, etc.

[CarlD]

3000 watts is a really large current at 12 volts. 3000/12= 250 amps. You have 2 LFP batteries rated at 100 amps max continuous and higher value surge ratings. I don't know the 2/0 wire length between the batteries and the inverter, but you may be experiencing a significant voltage drop at the inverter which could cause it to shutdown then start up again.

Now that you know it works and have some knowledge of the limits, you should be good to go. Happy camping.

[Huck]

Originally Posted by CarlD

3000 watts is a really large current at 12 volts. 3000/12= 250 amps. You have 2 LFP batteries rated at 100 amps max continuous and higher value surge ratings. I don't know the 2/0 wire length between the batteries and the inverter, but you may be experiencing a significant voltage drop at the inverter which could cause it to shutdown then start up again.

Now that you know it works and have some knowledge of the limits, you should be good to go. Happy camping.

This is something I put together 2 years ago, but then had to have my aortic valve replaced which set me back awhile. I'm finally ready to head to the beach and this was the 1st trial of the system to see if it would power the trailer as I hoped it would. I can also run an extension cord from the van to my Clam tent to run a fan and keep my laptop charged.

[John in Michigan]

Probably not surging to 3000 watts or not for long, otherwise the 175 fuse would have blown.

[Geronimo John]

[QUOTE=John in Michigan;819233]Other problem with just plugging the trailer into the inverter is the point that I think Gordon made. The inverter even assuming its capacity is large enough is only 80-90% efficient. Better to run 12 vdc using thick copper.

........
If considering the heavy copper approach, and your TV and Trailer uses different battery types, then a DC to DC charger would most likely be required.

Our 2019 Ford F-150 has a large AGM battery. Our Oliver has lead acid batteries. Once these batteries die, I'll replace them with AGM, and add the heavy copy wire approach connecting the two AGM systems with heavy copper, igination cut-off relay, slow blow fuses, and Anderson connections.