solar charge controller

Thread Starter

macataq

Joined Sep 15, 2007
11
hi
i am trying to make a solar charging station for my Black and Decker CM1000
rechargeable lawn mower. it has a 24v motor powered by 2 12v 17 A/H batteries. i have 12v 20W panel. what i would like to know is what size controller to get, a 12v or a 24v?
any help would be appreciated.

mac
 

Gadget

Joined Jan 10, 2006
614
The 2 batteries will be wired in series as a 24 volt battery, and a 12 volt solar cell wont charge this arrangement unless you can step the voltage up and then use a 24volt (20 watt min) solar charger ( with some power loss due to step up). Full charge would take more than 25 hours of full sunlight.
A better arrangement is to get another 12v 20 watt panel to wire in series with the first ... then use a 40 watt or greater 24volt solar regulator. This 40 watt arrangement would then only take somewhere around 12 or 13 hours of full sunlight to fully charge the batteries.
 

Thread Starter

macataq

Joined Sep 15, 2007
11
thanks Gadget

i am not concerned about the amount of time it will take to charge the system back to full charge, since i would only need to use it approximately
once a week. the thing i was concerned about was whether i needed to provide the voltage of the battery(12v) or the total amount of battery power(24v)
thank you for setting me straight

Mac
 

HarveyH42

Joined Jul 22, 2007
426
It might take the better part of a week to fully charge the batteries, in Canada. You can't expect to get more than a few hours of full-direct sunlight on the panels each day. Might be days where almost no charging gets done.

How much run time does your mower get off a charge? I've always wanted to pick up a cheap battery mower, add some drive motors, and make it automatic (robot). Never saw one running, so not sure if its worth the time or money.
 

Salgat

Joined Dec 23, 2006
221
Wouldn't you need a much higher voltage to charge the battery? For example, a 12V car battery requires some 18V from the alternator to charge it.
 

Nomad

Joined Oct 21, 2007
43
not hardly. the output of an alternator is typically regulated at 13.8v. some even lower (12.7 on some semi's) the electronics in a vehicle tend to start leaking smoke above 15 or 16v.
 

Gadget

Joined Jan 10, 2006
614
a panel rated at 12 volts typically puts out around 18 volts in full sunlight and most solar regulators either regulate the output of the cell to 13.8 volts, or dump the output of the array into the battery while monitoring the terminals, switching the charge off at a terminal voltage of 13.8 and back on at around 12.5. Double those values for a 24 volt system.
 
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