Renogy DC/DC MPPT help

[Amy]

First time posting.

I have a Roadtrek RV with an underhood generator (basically a second alternator) to charge one 100ah AGM house battery. I would like to add two lithium Battleborn batteries and solar to the setup. I have a wiring schematic that includes a Sterling DC/DC charger and I was wondering if anyone knew if I could substitue the Ronogy DC/DC MPPT charge for the Sterling in the current setup in the attached file. That way I wouldn't need a DC/DC charger and an MPPT charger.

Thank you.

 

[FilterGuy]

Renogy DC DC Charger w/ MPPT

Finally reviewed it! People asked me repeatedly, and I was too busy with the solar shed. For the last few days, I tested it like crazy.. And I love it! I should have tested it months ago. Works extremely well, and it's fool proof. I pushed it to every limit, and if it cut off, it would restart...

diysolarforum.com

 

[FilterGuy]

In the drawing it looks like the sterling has two charger outputs and the Renogy only has one. You would have to decide which bank will get charged when the selector switch is not on 1+2.

How old is the AGM? Is there a reason you are keeping it?

 

[Amy]

In the drawing it looks like the sterling has two charger outputs and the Renogy only has one. You would have to decide which bank will get charged when the selector switch is not on 1+2.

How old is the AGM? Is there a reason you are keeping it?

I would like the charge to go just to the lithium batteries since that is what I will have the MPPT set for(lithium batteries). So I would always have the battery switch set to lithium. The only time I would switch it to the AGM battery is if I want to run the AC with the underhood generator. So I would never have it set for both 1&2.

It is kinda complicated why I am keeping the AGM. The underhood generator is set to charge AGM batteries, not lithium. I would have to remove the internal regulator in the GU (underhood generator) and install an external regulator. A more complicated process. Plus leaving the AGM will allow me to run the AC when not plugged into shore power.

Now I could be wrong on some of this so that is why I wanted to see what others thought.

 

[FilterGuy]

Is the AGM hooked directly to the under-hood generator?

 

[Amy]

Is the AGM hooked directly to the under-hood generator?

I believe so.

 

[FilterGuy]

It sounds like you want to keep the two batteries separate till you need the AC and then connect them together.

I would not recommend that. If the two batteries are not at the same voltage you could get some pretty big current when you connect them together and they try to equalize.

 

[Amy]

It sounds like you want to keep the two batteries separate till you need the AC and then connect them together.

I would not recommend that. If the two batteries are not at the same voltage you could get some pretty big current when you connect them together and they try to equalize.

No, I want to keep them separate. Using the AGM only when using the AC with GU running. So I would have the battery switch on AGM battery only. Does the wiring schematic look incorrect?

Do you think I should leave it the way it is set up and add a separate MPPT controler?

 

[FilterGuy]

OK... that should work, but be careful never to put the switch into the 1+2 position.

 

[FilterGuy]

If you can find a high-current switch that does not have a 1+2 position, that would be even better.

 

[FilterGuy]

https://shop.pkys.com/Blue-Sea-11001-Battery-Selector-Switch-1-2-OFF-No-Both-position_p_3640.html

 

[Amy]

https://shop.pkys.com/Blue-Sea-11001-Battery-Selector-Switch-1-2-OFF-No-Both-position_p_3640.html

GREAT!! Thank you.

 

[backyardshane]

what if you let the under hood generator charge the agm and keep it separate from the lithium system then run the dc/dc/mppt off the regular cars alternator then have a transfer switch to determine which battery bank your drawing from?

 

[Sgt Raven]

what if you let the under hood generator charge the agm and keep it separate from the lithium system then run the dc/dc/mppt off the regular cars alternator then have a transfer switch to determine which battery bank your drawing from?

I don't see why the 2nd AGM alternator couldn't charge a LFP battery thru the DC-DC, it should take care of changing the charging settings. The DC-DC should be able to handle a alternator setup for FLA, SLA, GEL, or AGM batteries.

 

[Amy]

what if you let the under hood generator charge the agm and keep it separate from the lithium system then run the dc/dc/mppt off the regular cars alternator then have a transfer switch to determine which battery bank your drawing from?

Yes I plan to keep the batteries seperate with a transfer switch and to keep it simple I will just wire it all thru the inverter.

 

[Amy]

I don't see why the 2nd AGM alternator couldn't charge a LFP battery thru the DC-DC, it should take care of changing the charging settings. The DC-DC should be able to handle a alternator setup for FLA, SLA, GEL, or AGM batteries.

Thank you. That is how I plan to set it up.