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Diodes in Battery Charger Clip Lead


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Old 05-13-2018, 07:50:33 PM
Dwayne Oxford Dwayne Oxford is offline
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Default Diodes in Battery Charger Clip Lead

Got small taper charger plugged into receptacle controlled by light switch to charge mower batteries. There's continuity across clips when power to charger is off which drains battery. Which lead should I put diode in and which direction? If I understand correctly, DC flows - to +, so I'm thinking put it in the - lead so current can flow to battery but not back to charger?
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Old 05-13-2018, 09:40:04 PM
CharlieB CharlieB is offline
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Default Re: Diodes in battery charger clip lead

That sounds right.
I used to rig up stuff like that to keep my idle batteries charged. The trouble was that I always had to guess when the battery was charged. After I replaced several batteries prematurely, I realized that it was because I was overcharging them. I dragged myself kicking and screaming into the 21st century and spent 20 bucks for a little trickle charger/maintainer with a computer chip in it. It monitors the battery and only charges it as needed. I leave it plugged in all the time and my batteries last a lot longer. Spent $20 to save a lot more.
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Old 05-13-2018, 09:59:26 PM
DustyBar DustyBar is offline
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Default Re: Diodes in battery charger clip lead

You also need to remember that common diodes drop about 1/2 volt in the forward direction. You wouldn't think 1/2 volt less charge would be significant but it is something to consider.
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Old 05-14-2018, 12:20:50 AM
Thaumaturge Thaumaturge is online now
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Default Re: Diodes in battery charger clip lead

Idea may work well on a trickle charger, say under 2 amps max, but it would be a bad idea for a larger charger. As stated the typical voltage dropped across a conducting diode is between 0.5 - 0.7 volts. Think what that means in terms of heat. (Watts = Volts times Amps). On a 2 amp charger that means 1 to 1.4 Watts of heat needs to be dissipated by the diode itself. The 1N4000 series are rated at 1 Watt maximum... no safety overhead. So if you do it use a 1N5400 series.

The other reason it might be a bad idea is again that forward voltage drop. It reduces just how much charge you are getting into the battery. It would reduce say a 13.5 volt charge voltage down to a 13.0 volt charge voltage. (Out of spec on low end for automotive charging.) Recomended charge range is 13.5 to 14.3 volts.

As to which lead to mount one in, really doesn't matter at all. Current is same at any point in a series circuit.
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Old 05-14-2018, 12:43:54 AM
Scotty 2 Scotty 2 is offline
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Default Re: Diodes in battery charger clip lead

Quote:
Originally Posted by CharlieB View Post
I dragged myself kicking and screaming into the 21st century and spent 20 bucks for a little trickle charger/maintainer with a computer chip in it. It monitors the battery and only charges it as needed. I leave it plugged in all the time and my batteries last a lot longer. Spent $20 to save a lot more.
Sound like a plan Stan.
We have a few if these maintenance chargers on mowers and tractors and spare cars. Each charger costs less then a battery (if I had to buy a new battery).

Cheers Scott
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