Diode in charging circuit

[deardancer3]

I have a new 7 amp charger for my Headway 20ah pack that I am delighted with for several reasons, except one-- when It does not have 110vac applied it slowly drains the battery; this could be a problem in the winter as the bike is ridden less often.

My present fix for this is that I have inserted a big stud mount power diode in the charger cable that allows charging current, but blocks the drain from the battery. However after 10 minutes the "big honkin diode" gets pretty hot, too hot to hold but not hot enought to burn your hand if touched, but I am a little woried about melting somethin if it touched it. ( the charger voltage is adjusted to compensate for the diode voltage drop)


The diode must be dissapating about 5 watts as it drops .7 volts and passes 7 amps.

I am wondering if anyone can think of some other easy fix to the battery drain problem with no 110vac present, or, if this is as good as it gets, or if i should put a small heat sink on the diode increasin g the size of things, but decreasing the peak temperature.

any thoughts?


dick
colorado

 

[dnmun]

take the diode out.

why did you decide to leave the charger connected after charging?

if you do not want the charger to drain the pack down while leaving it connected to the charger, you need to open the charger and remove the drain down resistor across the output caps.

 

[Jeremy Harris]

take the diode out.

why did you decide to leave the charger connected after charging?

if you do not want the charger to drain the pack down while leaving it connected to the charger, you need to open the charger and remove the drain down resistor across the output caps.

I agree about disconnecting the charger, it's a very sensible thing to do.

The current leak probably wont be any capacitor drain down resistor, it will most likely be the voltage sense circuit that provides the essential feedback to hold the output voltage constant at the end of charge. So, don't go removing resistors from the output, or else you risk a serious over-charge problem by removing the chargers ability to hold a constant voltage at end of charge.

 

[SamTexas]

Sounds to me like you have the charger permanently installed on the bike. If so I would just install a switch on either of the charger outgoing wires.

 

[amberwolf]

I am wondering if anyone can think of some other easy fix to the battery drain problem with no 110vac present, or, if this is as good as it gets, or if i should put a small heat sink on the diode increasin g the size of things, but decreasing the peak temperature.

A simple switch is the easiest way, but if you want it automatic, then you could use a relay that turns on only when voltage is present at the AC terminals, for instance by wiring a celphone charger in parallel with the charger's AC terminals, so it is powered on when the charger is, and powering the relay from the celphone charger. Then wire the relay's contacts so the charger output is controlled by it.

Keep in mind it may have to be a hefty relay to prevent the contacts from burning up from arcing. But worth a shot.

 

[circuitsmith]

Hey Deardancer,

This is Tim in Wash. DC.

If you set on using a diode, get a schottky diode.
They have about 1/2 the voltage drop and dissipation.

 

[deardancer3]

Hey Deardancer,

This is Tim in Wash. DC.

If you set on using a diode, get a schottky diode.
They have about 1/2 the voltage drop and dissipation.

thanks tim, for my 30v 7amp charger I ordered the following off ebay/radio shack about $2.50 delivered with tax


NTE6080 - R-Schottky 10 Amp 60V #:NTE6080

after installation and testing, the temperature rise is down to only 45F for a full charge. that with a very small heatsink on the diode.

so, in the winter its only up to 90F.

thanks

d

 

[Xrain]

http://www.digikey.com/product-detail/en/RT314615/PB961-ND/1095285

Just use one of these for $3.60, this relay is powered off of 110V AC

So put it in place of the Diode in your charging circuit, and then parallel the coil wires of the relay with the AC plug going into the charger.
It can switch 16 Amps so it should be more than enough for your charger, and is rated to 430V AC which is good for ~ 200 V DC as a rule of thumb.

This should take any worry out of your charging. Just plug it in, and unplug it and everything works automatically.