Let's Make Robots!

Charge Controller Circuits

Hey folks, would any of you circuit-building guys start me in the right direction in terms of building a charger for a 10-20AH 12v sealed-acid battery? I think I have the basics down, but I could use a re-fresher... Trickle vs. Full and how does the charger know the battery is full? --I want to build a simple onboard charger for Walter and (really) I don't want to shell-out the 35 bucks they want for their little, stupid aligator clip charger. --Much love as allways for your knowledge!

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Maxim has a number of charger controllers that can be built into chargers, knew a couple of people that did so, but haven't myself.

The MAX1772 datasheet has some info on how to build either a micro controlled charger or a standalone, that should be capable of Lithium Ion, NiCad, NiMh, and Lead Acid charging. I picked this one because it was a QSOP package, looks like a regular dual inline surface mount, where some other chips in this category were QFN, surface mount with the leads under the chip. The QSOP package shouldn't be difficult to solder.There are some other QSOP and SSOP pacakages, but no DIP. 

What I decided on was to buy a Schumacher SEM-1562A 6-12 volt charger, for about $18-$20 from Walmart (can't find it on their site, but was near automotive in the store). I heard about this charger on a forum for some power wheels modders who would do things like this to their kids toys. Yes I was considering one time turn a power wheels vehicle into a robot. Note that charginglead acids can be hazardous without the right charger.

I've made chargers for these batteries before, the simplest way is a constant current charger. The current is limited to a safe value which should be printed on the side of the battery and when the voltage reaches at certain level it changes over to trickle charge.

Here is a fact sheet on the subject.

You should be able to get a plugpack for about $20 US that will do the job. (This was $30 AUD)

OR

I can design you one if you tell me the maximum charge current of the battery (SLA's can be damaged by excess charge current). This could be controlled by a picaxe if required. Do you have a car battery charger that can be used for a power supply?