I need to keep the batteries in our school bus topped off so they will last longer. Just simply trickle charge the two 8-D batteries and nothing more. It just sits under a shed and the batteries go down from not being used that often.I need to use solar since the nearest power (110v) is about 300 ft away. About how many watts would it take to keep the two 8-D batteries topped off year round? We are in the southeast USA, and the bus is 24-volts.One more thing... it seems wasteful to go from 12v solar to a 110v inverter, then back to 24-volts to charge the batteries. Thanks for your help.

Unisolar 24v 136w $99MS Sunsaver 24v controller $70#12 or #14 wire is probably fine with 4 to 5 amps max.I think the controller needs to be connected to the battery BEFORE the solar is applied. Need a switch on the solar to turn off before you disconnect from the bus.This system will safely connect the panel direct to the battery with no added inverter or charger.

What a deal on the panel.... THANKS

Hi,No need to use an inverter at all. There are lots of solar charge controllers that will work magnificently @ 24 volts.I'd recommend about 120 watts per 100 amp-hours of storage @ 24 volts. That probably means about 320 watts of panels.

I thought 100 watts would keep them trickle charged...

Hi,An 8 D is usually in the 250 amp-hour range. For the rock bottom wattage about 60 watts might keep them charged, but only in PERFECT solar conditions. It also depends on the chemistry. Are they AGM or flooded?

Bus battery charging... | Good Sam Community

15 Replies

Gulfcoast
Explorer
Feb 13, 2015
Update: Electrician is coming to install a new 110v. line to power the battery charger... no solar.
Gulfcoast
Explorer
Feb 13, 2015
Shipping on the large panels is about what the panels cost, to the east coast.
time2roll
Nomad
Feb 13, 2015
There are plenty of larger ~240w panels on the site for about $50 more but shipping will kill ya.
I assume that Unisolar is much easier to ship.
Chris_Bryant
Explorer II
Feb 13, 2015
smkettner wrote:
Unisolar 24v 136w $99

MS Sunsaver 24v controller $70

I'm going to pull some data from RDS*, and say this would be perfect for maintenance. Not enough to recharge, but plenty to keep it topped off.

*My favorite acronym..
Gulfcoast
Explorer
Feb 12, 2015
They are wired in series. I used a 4 amp 24v charger and my gen to build them back up today... only took 4 hrs and the float light was blinking.
time2roll
Nomad
Feb 12, 2015
I assume they are in series, no balance issues.
pianotuna
Nomad III
Feb 12, 2015
Hi,

Flooded exhibit more self discharge than AGM. They also want more charging as they age. 120 watts per 100 amps @ 24 volts would equalize them.

Are they wired in a balanced manner?
Gulfcoast
Explorer
Feb 12, 2015
I'm going to check for a parasitic drain in the morning, then we will know more.
time2roll
Nomad
Feb 12, 2015
If the 136w does not keep them up you can get a second panel to feed the same controller.
Depends also if there is much parasitic drain on the battery or if battery is disconnected.
I honestly think 100+ watts will be fine.
Gulfcoast
Explorer
Feb 12, 2015
Flooded

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Bus battery charging...

15 Replies

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