DC only ATS (no AC) for RV

[MReimler]

I'm looking for a DC only 50 amp Automatic Transfer Switch to switch between the shore power converter & the solar MPPT. I've searched & found plenty that switch between grid (AC) power & solar, or ATSs that switch between shore power & inverter, but nothing that's just DC.

Seems like there should be something out there but I can't find it.

Any help is appreciated.

 

[Bobert]

I'm looking for a DC only 50 amp Automatic Transfer Switch to switch between the shore power converter & the solar MPPT. I've searched & found plenty that switch between grid (AC) power & solar, or ATSs that switch between shore power & inverter, but nothing that's just DC.

Seems like there should be something out there but I can't find it.

Any help is appreciated.

That sounds expensive If you can find it. Chan I ask why you want to do this there might be another way to accomplish the same goal.

 

[Ampster]

Seems like there should be something out there but I can't find it.

That is not a common need to be done automatically. It could be done with a simple DC AB switch. If the purpose is to charge the batteries the Voltage settings on both of those devices should move the electrons without over charging the batteries and without the complication of a switch.
Physics is your friend.

 

[timselectric]

It's a simple thing to implement. But, it's very expensive due to the issues with switching DC circuits.

 

[Shimmy]

A DC (automatic) transfer switch is hell on the switching contacts. Usually a better way of doing it is blocking diodes so the two sources share power, and if you want to disable the shore power input then add a contactor on the AC side to isolate that. You could get away without the blocking diodes if the two sources can parallel.

 

[rmaddy]

If the purpose is to charge the batteries the Voltage settings on both of those devices should move the electrons without over charging the batteries and without the complication of a switch.

The problem is the possibility of the combined charge current coming from two sources being higher than the max recommended charge current of the battery bank.

There's nothing wrong with having multiple DC charge sources but all of the charge sources have to be set correctly to avoid pumping too much current into the batteries.

 

[timselectric]

I originally had planned some solar switching in my system. But because solar is cheap, I decided to keep it simple and reliable.

 

[Ampster]

The problem is the possibility of the combined charge current coming from two sources being higher than the max recommended charge current of the battery bank.

That is a good point that could be mitigated with settings. On the other hand I assume the only reason one would use shore power to charge batteries would be that there was no solar. However is is always good to plan for the worst case to be safe.

 

[rmaddy]

On the other hand I assume the only reason one would use shore power to charge batteries would be that there was no solar. However is is always good to plan for the worst case to be safe.

I was thinking the same thing. No need for shore power if the solar is working. But sometimes the solar isn't enough and a little shore power can help. Either way you need to ensure the two sources together can't overload the batteries.

 

[timselectric]

Charging from the grid is my last resort.
Second to last resort, is a 48v alternator connected to a stationary bicycle.

 

[MReimler]

That sounds expensive If you can find it. Chan I ask why you want to do this there might be another way to accomplish the same goal.

I'm trying to avoid "double" charging the batteries when I'm plugged into shore power. It's simple to switch off the solar when I'm plugged in but I was looking for a more elegant solution.

 

[Ampster]

I'm trying to avoid "double" charging the batteries when I'm plugged into shore power. It's simple to switch off the solar when I'm plugged in but I was looking for a more elegant solution.

An complex solution could be a contactor on the solar that is disconnected when shore power is connected. The problem with that is the constant draw of the contactor coil while charging with solar. However before I did that I would do the math to see what the current outputs are from each source and see if both of them exceed the capacity of your battery. If not then that is both a simple and elegant solution. Depending on the type of batteries some tweaks could be slight voltage setting differences.

 

[timselectric]

I wouldn't switch off the solar.
As long as it's available.

 

[Bobert]

I'm trying to avoid "double" charging the batteries when I'm plugged into shore power. It's simple to switch off the solar when I'm plugged in but I was looking for a more elegant solution.

Could you put a daylight sensor on the ac side of the converter charger so that it would be off if enough solar is present to activate the solar panels?

 

[Ampster]

I wouldn't switch off the solar.
As long as it's available.

I would not do that either unless the current from both sources is going to boil the acid of my FLAs or overheat by Lithium batteries.
I assume we are working with the safety parameters that @rmaddy outlined? If not then anything goes.

 

[timselectric]

I would keep the solar going and not use the shore power for charging.

 

[MReimler]

Thanks for all the replays! I'll either just turn off the solar when connected or do some battery research/settings & leave then both on.