Charging cut off / watt meter

[Cryofix]

All,

I charge my A123 cells on a Mastech 2050 its a 20 amp 50 volt ac to dc converter and I can charge a 10S2P in 15 minutes however....

I need a piece of electronics that sits between the battery and the ac/dc converter that is very similar to a watt meter but with more features, such as an automatic switch to shut the current off (Ive put 4000+ mah into a 2300 A123, not good) when it reaches certain voltage, I am just looking to add logic to a watt meter essentially.

anyone know of anything like this? is it easy to make casue I can solder and semi understand schematics.

Please let me know

Thanks,
Ed

[mjws]

Your Mastech is a CCCV supply. When your batteries hit target voltage, it will reduce current to (near) zero i.e whatever current is necessary to counteract self-discharge. No need to put logic in to cut it off CCCV charging can be left on indefinately. Makes no difference at all what the wattmeter says.

The daptor by skelectronics http://www.slkelectronics.com/lipodapter/index.htm will cut at 3.6V for you, but you are skipping the whole CV portion of the charge.

[nzreg]

Do you mind if I ask where you bought your Mastech?

[Cryofix]

A123 pack charge voltage is 3.6 and nominal 3.3 I charge a 36.5 on a 10S, but the batteries tendencies are to settle at nominal 3.3. very quick, so a charge is still going in at .1 amp rate or so this can casue an overcharge condition if i forget to check the pack while charging.

After I charged my pack to 4000+ mah its was at 40 volts, I had to quickly dishcarge to get it back to its max 3.6 level.

I know A123 cells are much safer but I wouldnt mind something to make me more idot proof.

[Cryofix]

Do you mind if I ask where you bought your Mastech?

I picked it up on Ebay for $269 US with shipping

also www.tanicpacks.com used to sell them not sure why they don't have them anymore.

[mjws]

Very strange. Your mastech should never let the voltage go above 36V if that is what you had it set too. When the battery settles it is correct for the mastech to add current until it reaches 36v. It isn't possible for a 36V source to charge a battery to 40V. I charge from a dumb 36V source often. There is no way for an overcharge to occur even if I leave it hooked up for days. I would have thought your rig is much more accurate was it set wrong?

Been running A123's since pretty close to day 1. 4V a cell is no big deal and won't even lose you a cycle. The only real way to idiot proof it is to add a charger. There is no ready made hardware that works inline like you want.

Mike

[Cryofix]

I actually got it, Talked to Sid at SLK electronics, he made the suggestion to use an egg timer, so thats what I did sort of......

Had an old Hobbico 905 charger laying around hasn't been used in years ( http://www.hobbico.com/airplanes/hcaa2051charger2.jpg ) cracked it open, removed the 15 minute timer from it snipped the ground wire on my watt meter than ran the timer in series with the ground wire, wa laa I got a 15 minute quick charger with a watt meter readout.

This is a great "safety" precaution for me anyway as I tend to forget about charging batteries as I am talking at the field or something, at least this gives me some piece of mind.

Thanks for all your advice and input.