Is there a good way to drain the battery for cycling with a "dumb" charger?

[kaypee171]

I have built my own dumb charger for my battery, and it has helped somewhat. However, I feel I need a "dumb de-charger" to extend the life of my battery as much as possible. I know Mike's Charger has a setup that uses a shop lamp (?) to safely drain the battery for complete cycling. Is there a recommended/affordable way to do so?

[eq1]

Not that I know of. But I was wondering if you could get a decent drain by letting the car sit with the lights, other accessories, on, while the DC-DC converter is engaged? Seems like sometimes when the car is sitting with the key on, such as in autostop, the DC-DC converter remains engaged and you get a 2-3 amp drain on the HV battery. Sometimes it doesn't seem like the DC-DC is engaged and you get no drain on the HV. But anyway, DC-DC engaged, lights/accessories on, 3 amp drain, let car sit - if it can do this you could get a consistent drain perhaps down to 1.04 volts per cell(?) - as far down as the car will allow. Problem with draining when driving, it seems, is that the discharge amperage is hard to control at a low level, so the pack voltages get pulled down low prematurely...

[olrowdy01]

Originally Posted by eq1

Not that I know of. But I was wondering if you could get a decent drain by letting the car sit with the lights, other accessories, on, while the DC-DC converter is engaged?

If the grid charger battery leads don't have diodes in them (it seems that some people do that as a safety feature) and the battery leads in the harness are thick enough to handle a few amps couldn't you just connect the external load to the battery harness?

If the current is only an amp or two would the battery fan need to be run? If so make up an adapter cable to connect only the fan leads from the grid charger to the battery harness.

The adapter cable could have the actual battery leads split off to connect to the load and also run the fan from the grid charger.

[eq1]

I think the biggest concern with discharging is being able to tell when a single cell reaches the critical low voltage, beyond which the cell will likely be damaged. It's a pretty likely scenario, considering that we're dealing with weak, probably unbalanced packs. So unless you got some computer program and monitoring system, connecting an external load is pretty risky... Theoretically, trying to discharge as much as possible with the IMA system leaves it up to the BCM (or whatever computer/s) to prevent too much discharge...

[Eli]

A 100W lightbulb works well.

As eq1 says though, the danger is overdischarging the weakest cell in a pack. Proceed with caution....

[olrowdy01]

Originally Posted by eq1

I think the biggest concern with discharging is being able to tell when a single cell reaches the critical low voltage, beyond which the cell will likely be damaged. It's a pretty likely scenario, considering that we're dealing with weak, probably unbalanced packs. So unless you got some computer program and monitoring system, connecting an external load is pretty risky... Theoretically, trying to discharge as much as possible with the IMA system leaves it up to the BCM (or whatever computer/s) to prevent too much discharge...

I agree. It is more complicated than just putting a load on the battery without monitoring the battery. [Slapping forehead.]

"Exhilaration is that feeling you get just after a great idea hits you, and just before you realize what's wrong with it." -Rex Harrison

[kaypee171]

How does Mike's setup work? Does his harness tie into each stick? I could buy his harness if that would help, as I would like to have his charger eventually.

[Eli]

Originally Posted by kaypee171

How does Mike's setup work? Does his harness tie into each stick? I could buy his harness if that would help, as I would like to have his charger eventually.

No. It watches the rate of voltage change very closely.

If you suddenly lose a volt, you know you lost a cell.