making a battery charger? questions

I have a power supply / battery backup used for alarm systems that i was thinking about using as a battery charger for my Craftsman. Plans are to mount to supply under the hood so all i have to do is plug the mower in to the wall outlet to charge it. This is a 12v charger. Does anyone have any reasons this wouldnt work out for me? This will be a temp. solution for my old mower. Something is draining the battery down quickly, and I plan to replace the mower next season. I just dont want to dump a bunch of money into this to fix it when its getting scrapped next year.
Thanks for any input here guys!

I think the heat would kill the charger. My opinion, which is worth exactly what you paid for it, is to mount the charger on a wall next to where you park the mower. Put a long pigtail on it and plug the mower into it.

seeing as this is will most likely be a very slow charger, and not much power passing thru the cables at one time, do you think the semi-thin wires will be ok? Your idea is probably better than mine, i just have to go buy some wire to extend the leads on the charger and some spade terminals to connect them. No big deal tho.

Craigdavid said:

seeing as this is will most likely be a very slow charger, and not much power passing thru the cables at one time, do you think the semi-thin wires will be ok? Your idea is probably better than mine, i just have to go buy some wire to extend the leads on the charger and some spade terminals to connect them. No big deal tho.

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What is the output of the power supply you are thinking of using? What is the gage of the wires coming out of your mower? When I think of power supply I think of those UPS types that you use to power computer systems, etc in case of power loss.

We all know how manufacturers use the smallest size wire possible without catching fire, chances are this wire size will be just fine for your use. However, if the extended wire will be more than a couple feet long, then I'd use at least the next size up. May I offer a suggestion for the plug you put on your mower? I used to have a full dresser motorcycle that would drain a battery in three weeks, so I bought a trickle charger, mounted it on the wall where I parked that bike, and installed a rubber two wire plug on it. That way all I had to do when I came home was to simply plug it in to the charger, then plug the charger into the wall. This type plug will have one exposed terminal and one that is covered, make sure the exposed terminal is connected to the negative battery post.

I don't know what your chargers output is, but I'm thinking it's probably in the 300 to 500 mA range, which converts to .3 to .5 amps respectively. My trickle chargers full output is 1.5 amps, but cycles off and on in the float mode at .5 amps. Your charger should work, however you may have to give it plenty of time in between mower uses.

Let us know how it works.

JDgreen said:

What is the output of the power supply you are thinking of using? What is the gage of the wires coming out of your mower? When I think of power supply I think of those UPS types that you use to power computer systems, etc in case of power loss.

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this is the supply i will be using. The only output it shows is just 12v DC. I would guess its about a 16 gauge wire on the supply itself. The battery cables on the mower are the standard 8 gauge wires. I plan on making some pig tail wires to connect to the mower and leave on there. Then I will extend the power supply wires, so all I have to do is park next to it and plug her in. And i will keep the + wire covered to keep from shorting anything out.

Buy.com - CyberPower CyberShield CS24U12V DC Power Supply

That has a 2 amp output... But it is only 12 volts DC... you need 13 volts to charge your lead acid battery...So it will never fully charge.

Also like mentioned by mullins87, the Heat will kill it... max storage heat is 113 degrees F... Max operating temp is 95 degrees F... Don't mount it around the engine... :smile:KennyV

A charging circuit is a little more complicated than just a power supply. You'll need some other components. I built one once a long time ago. I can't remember what it takes but I know you need a capacitor and a diode in there somewhere.
What you have may work, but you'll never know if it's fully charged or it could over charge. Your going to have to be careful and remember not to leave the battery connected or risk losing it.
You can get a charging circuit cheaper than you can build one and you can get a maintainer (trickle charge) for less than you can replace the battery. So trying to save money there doesn't really add up.

If his backup power supply is built anything like the one next to me now, it has a small 12v SLA battery in it. A battery charger doesn't know the difference between the little 6 Ah battery in the power supply or the 150 Ah batteries I have in a small shop. I also have a rechargeable spotlight with two 6v SLA batteries wired in series, obviously making 12v, and one of those portable jump start batteries with the short jumper cables, I'm assuming it has one 12v SLA battery in it. The chargers for those devices both use those small plug-in transformers. Both are rated at 12v, but we know the voltage must be at least 14v or more to "push" that charge into the batteries. Granted, I have never put a probe on one to see what the output voltage is, but since they work I assume it's over 12v.

Craig, when does the battery drain? After it sits or while you're using the mower? Does it have an electric PTO? Have you tried to find the problem? I've had two older mowers that wouldn't recharge the battery. In both instances the spade connector on the alternator wire rusted off where it plugged into the battery circuit at the solenoid. I simply put a new connector on and fixed the problem. One of those mowers lasted another 12 years before I parted it out.

The battery drains when I am mowing. The mower will just shut down and be completely dead. it does it about every 2nd or 3rd mow. I have been taking the battery to auto zone to charge it. If this charger will work just enough to get me thru the next 5 or 6 mows, that is all I need. I plan on buying a Deere next spring. This Craftsman was a hand-me-down that used to be used like a bush-hog in a really rocky area. The cut is uneven, blades are terrible, trans is going, won't hold a charge, smokes like crazy, bla bla bla.