question

garp avatar image
garp asked

Question about changing battery types using a SmartSolar MPPT 100V

Hello,

Hopefully my issue is simple as I'm using what appears to be a simple setup compared to some of the ones I've seen addressed here.


I am using a harbor freight 57325 100W solar panel and the trailer had a single 12V tongue mounted battery in a tiny teardrop trailer. I'm using a SmartSolar MPPT 100V 20 amp 12-24-Volt Solar Charge Controller and it's worked perfectly the past year. I've just changed that to two 6-volt Interstate GC-2 AGM Batteries wired in series relocated from the external of the trailer to the interior. Do I need to change the setup or programming on my charge controller? I'm seeing it charge in spikes and if I recall correctly, it would normally just charge constant. I have been connected to the solar panel for a week and not seeming to get any recharge going.

I have the charger presets set to AGM spiral cell, is that correct for this situation?

MPPT Controllers
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
snoobler avatar image
snoobler answered ·

I'm assuming you've upgraded from a small battery to these batteries. I would expect that you have substantially increased your battery capacity. The behavior you're observing is likely due to insufficient PV to properly charge your battery possibly complicated by increased utilization.

The spikes may be a result of a poor connection between the MPPT and the batteries. Wire needs to be sufficiently sized, and all connections need to be properly torqued.


Charging ability:

100W solar panel:

100W/14.4V (charge voltage) = 7A (rounded)


Your batteries have 210Ah of capacity - that's 30 hours of charging from empty assuming your panel puts out a full 100W (it won't).


Lead acid batteries like to be charged at about 10-30% of their capacity depending on manufacturer/type. This would be 21A in your case. That's about 3X as much as you have available in perfect conditions.


You have way too little solar for your battery.


AGM Spiral is a special type of AGM. I doubt your batteries are this type.


Recommend you contact Interstate for absorption and float voltages. In the absence of manufacturer info, I would enter a custom battery profile:

14.4v absorption

13.8V float

4A tail current

Equalization disabled



2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.