AGM Batt on Trickle Charge?

AGM batteries have a much lower self discharge rate than a conventional deep cycle and if fully charged should be good for many months. Ours is fed by a 185W solar panel going through a Morningstar MPPT controller and I will hook it up every moth or so for a day to bring it up to 100% SOC. There is zero load when the batter cut off is off other than the Victron battery monitor.

westend wrote:
The Powerfilm is way over-priced for what it is. If you absolutely have to have a flexible module (backpacking in with lots of other gear), search around for a Unisolar module.

When he said "flexible", Unisolar was exactly what I thought about.

Don't know which one weighs less, but when I look at the price of Powerfilm - OMG! Talk about "expensive" Unisolar at $2 per watt ...

Powerfilm has a controller included, but this kind and this brand of controller (meaning - no brand) sounds like one of those $15-20 from Ebay.

The Powerfilm is way over-priced for what it is. If you absolutely have to have a flexible module (backpacking in with lots of other gear), search around for a Unisolar module. The company went belly up but there are still some modules on the secondary market.

Unisolar 68W thin film on E Bay= $149/shipped

The entire system - including battery - is outside. A simple on-board temperature sensor should be enough. No need in remote temperature probe.

Hi,

The other route is a charge controller with a battery temperature probe. It will cost more but it will provide optimal voltage all the time.

Something like This.

You probably know - laptop is consuming a few times less power when in Airplane mode with network disconnected. Don't stay connected unless you need to.

I would still get a controller if you expect to leave it charging unattended.
Otherwise good to go.

Different AGM have different setpoints. Check your battery manual. In any event, without a controller the voltage will be off most of the time. It will charge it, but the battery life will shorten. With el-cheapo PWM controller from Ebay the voltage may still be off, because those usually have fixed setpoints, but this is better than without a controller.

Another reason to get a controller is current. There is a maximum charging current that AGM battery can tolerate, for 18 AH it would be around 1.8A. Without controller your panel may exceed it sometimes.

I recall some small PWM http://www.solarblvd.com/ weather-proof controllers by Xantrex, Morningstar and Steka. Those are normally used for panel-mounted applications, and are outdoor rated. Weight around 4 oz.

A battery totally out of use would be a candidate for a TRICKLE charge. Days and weeks and months out of service. No discharges at all.

You intend to put your system to use. Discharge and Charge.

At (80F) an AGM can endure 13.4 for trickle purposes
At (20F) an AGM would need 13.8 for trickle purposes

As cheap as PWM chargers are these days I would buy TWO tiniest PWM's, one for summer and the 2nd for winter. Leave the WINTER one alone, the voltage would be about right.

When the panel supports the battery in MAINTENANCE TRICKLE-ONLY charge I would adjust the PWM charger to the voltages listed above.

A fully automatic charge controller is about as likely has having a fully automatic wife.