The math tells me 1.3 amps / 170ma = 7.64 hours charge time. That is what I learned in college 40 years ago about lead acid batteries not sure that applies to new technology NiCad batteries?
Ahhh...an RC glow plug battery charger. I gotcha. I'm in that boat myself, 'cept I haven't burnt out a battery yet
I've worn a few out over the years, frozen a few, ran over a few, but not burnt them out due to an overcharge.
Also true, that's what the math tells you, but I've always gone by the +25% "rule" and it's worked for me so far, since about '88 or so. Add that 25% and you get ~9.55 hours. 1-2 weeks...ooofff...not good.
The cheapo glow plug chargers aren't much more than a transformer, rectifier, a current limit resistor. Don't know exactly how they spec the one you've got, but let's assume it's 170mA short circuit and 3.35v open circuit.
In theory, that's a 19.7 ohm resistor in series with the output. At the start of the charge, you're getting the full 170mA, assuming the NiCad is still good, it'll come up to 1.2v fairly quickly. 3.35v - 1.2v = 2.15v. 2.15v / 19.7ohm = ~110mA charge rate. Later in the charge, the battery is actually at about 1.4v. 3.35v -1.4v = 1.95v. 1.95v / 19.7ohm = ~100mA charge rate.
When the battery is fully charged, it'll have a voltage across it of about 1.5v. 3.35v - 1.5v = 1.85v. 1.85v / 19.7ohm = ~93mA charge rate.
So, as you can see, even with a fully charged NiCad in there, the charger is still trying to push about ~93mA across it. That's less than C/10 for the battery, but still pretty far above the rate at which it can stand to be continuously on charge, and as noted in the technical desciption above, they'll start killing themselves.
Here is part of the dilemma. I use the battery on the weekend only, about 1 to 2 minutes each time, about 8 times total, on a model airplane glow plug.....(snip).....OK maybe there is something I don't know about batteries, maybe it has to do with the type of battery being used.
No, I think you got a pretty good handle on batteries, just maybe not so much the way they get charged up.
Batteries have 'internal resistance' which is what limits their ability to dump current. Alkaline batteries have a high internal resistance, meaning you can only get X amperage out of them. NiCads, NiMH batts, etc. have a very low internal resistance (good batts anyways) meaning you can really pull a lot of amps out of them. Connect a bunch of alkalines in parallel, you effectively lower the resistance and increase the amperage you can get from a bunch. So, you've got the right idea as far as alkalines go, just not so much the reasons why. (P.S. Lead Acid batteries act much the same as alkaline batteries as far as discharge voltage curves go)
Also, alkaline batteries have a very soft voltage drop off when they're getting discharged. NiCad, NiMH, have a very sharp dropoff. In other words, if you've got a light bulb hooked up to 2 batts, 1 alkaline, 1 NiCad and, all other things being equal, watch the lights as the battery goes flat, the alkaline light bulb will slowly dim out, whereas the NiCad will almost shut off like a switch was thrown.
The new technology batteries are different, I can get 60 amps form a batteries and do that over and over several times and still get 60 amps each time on the work bench right to the end. Then without warning the batteries is suddenly dead.
...which flows right along with the sharp voltage drop off of NiCads.
My old batteries is shot, I am going to buy a new NiCad battery it is 1.43 volts and comes with its own charger. I don't want to over charge it but I don't know how to do that since I have no clue how much power remains in the battery after I use it several times. Maybe I should run the battery dead with a light bulb then recharge the battery with a timer.
I've been doing good with the old school wall wart battery chargers on my glow plug lighters, but then again haven't left them on for days on end. There are 'smart chargers' out there for the glow plug lighters. They're a bit spendy, but how much more than a new set of plug lighters? I dunno...