OEM solar trickle charger panel replacement

[Oldchinahand]

I posed this question to the forum about a year ago. To everyone's credit, there were a number of responses, most of them well meaning altho outside the scope of the question and, no offense, MEAGO inducing. Going to try again.

We have the original 10W trickle charger roof mounted solar panel. The indicator light on the OneStop is bright when the sun is. My multimeter tells me we are getting 5W from the noontime AZ sun.

Two 12V Interstate AGMs roll our Cummins.

Four 6V deep cycle Interstate AGMs series/parallel provide our coach needs. When boondocking, a portable 200W Renogy suitcase keeps those deep cycles in the green zone.

Now the question: What is the largest panel wattage can we replace the OEM panel with WITHOUT running new wiring, controller, etc. Just want to disconnect the old 10W, and connect a new panel. What size? 10W? 15W? 25W? 50W? Of course, we could put another 10W panel up there, but I don't believe it is up to the job sitting alongside the garage in between adventures.

Fair Winds and Following Seas

[creativepart]

Since that panel doesn’t have a controller you need to use a panel that outputs no more than approximately 13v. For instance most 100 w panels generate 18v to 21v. Too much for your batteries to accept without a controller. And those 100w panels are considered “12v nominal” panels.

I don’t know what wattage panels will keep you under that voltage. But that should help you to know what to look for. I don’t know if replacement low wattage panels are still available. RV manufacturers stopped installing these quite some time ago.

It seems 10 - 15 watts is what every manufacturer installed back then. Must have been a reason.

[Bones2003]

I don't know if this is true or not but it came from the internet so it must be accurate! You don't need a charge controller if you have less than 5 watts of solar power for every 100 amp hours of battery capacity. So if your 4 deep cycle batteries are 100AH each, you can go with a 20W solar panel.

[MadMaxWinny]

Yes, your biggest issue is 10W for a 400+Amp-hour bank. If I were sizing for a solar float charge (zero load replacement), I'd shoot for a minimum of 40W, considering your climate. You didn't state what gauge your wire is, but if it could handle the current, a very cheap voltage controller would be a good idea. Unrestricted voltages above 14.6 for long periods of time could shorten the lives of your AGMs.

[Oldchinahand]

Have been out of pocket for a while but felt the need to "circle back" and offer thanks to creativepart, madmax and bones for your observations.

In the interim, since we were gifted a 25W panel a year or so ago AND the box just sat on a garage shelf and stared at us, I picked up a small HD controller and replaced the OEM 10W panel with it.

Seems to be able to keep up with parasitic draw and kitchen vent fan (which we run 24/7). Thought it was not keeping up with the starting batteries, but close observation determined our OEM Trik-L-Start (Rev D) had failed. Interesting, concerning tale there. Putting that in a different thread.

Fair Winds and Following Seas