Using an old psu as a lawn mower battery charger

[phil0083]

Hi all, i know this isn't particularly about psu's and more about battery charging, but I figured that this would be the best place to ask, since there will be a psu in the equation.

I have a lawn tractor that doesn't like to keep its own battery charged, I have tried new batteries ultimately ending in the same result, over time they will just wind up dead as a doornail. From what I've been told, a lawn mower engine has what is called a magneto that acts like an alternator for the battery and some how the one in my lawn mower has failed one way or another.

I've ordered a charge controller that will handle 12v, 3amps of power and has overcharge/reverse discharge/voltage regulation protection features as well and I had planned to pair it with a solar panel but lowes didn't have a solar panel for me and after some thought i kinda have decided to ditch the whole solar aspect of it.

I have an old psu(450w) that will supply 14amps on the 12v rail which seems more than adequate, but can i take the 12v rail of this psu and wire it to my charge controller and then from the controller to the battery and be fine with it? I know it would be painfully inefficient as this psu would be sucking more than what is probably needed out of the wall outlet, but this would be temporary until i can find or purchase a 12v ac/dc brick adapter with around 2-2.5 amps of output,then I can swap out the psu for just the ac/dc adapter.

Questions, comments and suggestions will be appreciated! :-D

 

[inzone]

Hell of a brainstorm you have come up with but there is one problem with that idea and it's that there is no regulator to regulate ther current coming from the psu into the battery so it would blow up the battery or severly overheat it and boil the liquid inside.

 

[Guest]

it would depend on the battery you are charging
12 Volt Charger Sizes
2nd paragraph

Most battery manufacturers recommend sizing the charger at about 25% of the battery capacity (ah = amp hour capacity). Thus, a 100 ah 12 volt battery would take about a 25 amp 12 volt charger (or less). Larger chargers may be used to decrease charge time, but may decrease battery life.

http://www.chargingchargers.com/tutorials/12-volt-charger.html
so the battery would need to be at least 56 ah (14/.25)

 

[popatim]

get a cheap charge maintainer or trickle charger for about $20 and use that. A regular charger left on for long periods of time will cook the battery.

(I wonder about my own battery now, I havent had to mow in a month thanks to this drought)

 

[Guest]

hold it, i just realized you are going to have the charge controller in the supply chain. it would depend if it will handle a 14 amp load coming in. and since you were going to use it for a solar power set up; i do have my doubts, that would have to handle a lot of panels.

 

[phil0083]

I've ordered a charge controller that will handle 12v, 3amps of power and has overcharge/reverse discharge/voltage regulation protection features as well and I had planned to pair it with a solar panel but lowes didn't have a solar panel for me and after some thought i kinda have decided to ditch the whole solar aspect of it.

^^^ I told you guys that i had a charge controller coming... at least you realized it looniam. All of you only read the very first line LOL, only when looniam squinted his eyes after he had posted did he see the words "charge controller" lol

I was just going on the basis of most devices just draw whatever amount of current is needed(3 amps) and not just accept the max amps given (14 amps) and burn itself out. But that's the thing, I'm not too sure on that. and that's why I also purchased a charge controller as to prevent overcharging and cut off the flow of power to the battery until it needs more charging.


the only thing i'm going on is the fact that if I can hook up a small pc blower fan directly to the 12 volts rail(which can supply a max of 14 amps) that works on 12 volts and draws about 0.27 amps and it not blow up, then why shouldn't I be able to hook up a 3 amp max charge controller and it only draw 3 amps (or slightly under for a buffer idk) and then feed it to the battery and then the charge controller cut off power when the battery is full and remains on standby until the battery starts to drain again.

 

[Guest]

oh duh. it will draw only what it needs being regulated by the charge controller . . this has been some embarrassing posts i've made here.

the danger is the battery getting overloaded and causing a combustion. with my lack of understanding of the charge controller; i would expect it to have the capacitance and resistance to deliver a safe load on the output. and with the PSU only delivering what is needed; it wouldn't overload the controller and burn it out.

go for it, just be safe the first time and prepare for the worse; either the battery or charger goes boom.

 

[phil0083]

Lol it's ok man, it happens to the best of us. Yea, I was just kind of looking for you guys to confirm my suspicions. btw nothing to a charge controller. all it is is a microcontroller sitting on a circuit board inside a box with positive and negative leads in and out. A + and a - lead for incoming "raw" power and a + and a - lead for outgoing "clean" regulated power. The micro controller can detect the battery's voltage and determine whether or not current should be flowing to the battery as to prevent over-charging. it also regulates the voltage to the specified range it is advertised for. and also prevents the battery from discharging itself back through the unit.

So basically its a overcharge protector/voltage regulator/discharge preventer/battery monitor all-in-one.

This is the one I purchased, it is advertised for a solar panel which I still might do in the near future, but i don't see any reason why this thing wouldn't be compatible with direct incoming current.

http://www.amazon.com/dp/B004XCZN5S/ref=asc_df_B004XCZN5S2105516?smid=AU5MW0P13QZ5V&tag=dealtmp759715-20&linkCode=asn&creative=395129&creativeASIN=B004XCZN5S

 

[Sertha Vinma]

The features are Cordless lawn mower, removable battery for easy charging and storage and fully collapsible multi-position handle with quick clamp. www.aucklandlawnmowing.co.nz