Hello Jos
The way you make packs for high amp draw is end to end solder them. use a
solder with some silver in it. deans makes solder for this application.
Granted you can not leave the pack in parallel with lead acid for long,
charging is a problem. i am saying i would use the NiMh pack as a jumper
pack, to just aid in a cold, or perhaps hot start. Charging would be
accomplished with a delta peak charger designed for NiMh cells.
If the pack was going to fail, it would fail when starting where you could
probably draw 40 to 75 amps?
These cells are sub c cells. they are smaller than c cells. I under stand
that if you were able to maintain 14.4 volts under load to the starter, and
the motor did not start and you ran the starter for minutes you could hurt
something. If the lead acid only lets say could provide 10.5 volts under
load, my proposed paralleled NiMh pack perhaps would elevate it to 11 or
11.25 volts? It by itself could probably not start the Europa, just like a
car that is doing the jumping could not start a car without the battery in.
too much resistance from the jumper wires. well the NiMhs are only going to
act like a jumper car, in your pocket that weighs in under 2 pounds. Now for
running it at 3 amps for back up fuel pump. It is going to act much like a
car battery. You can have a dead as a doornail car battery that has not a
chance of starting a car, but it will easily run the windshield wipers. well
a 3 amp draw on the 2600ma pack is very low for it. this is life critical
load. You could have a few marginal cells and still give you 80 or 90% C at
a 3 amp draw. Either end to end soldering or soldering using a jumper, if it
works for starting current, it will work for fuel pump draw.
The NiMhs probably have alot higher internal resistance compared to the
lead acid. Amps will flow from a pack if you drop voltage. you drop voltage
of 12 cell NiMh pack from 14.4 to 10.5, amps will flow. Drop voltage from a
full charged lead acid with 13.7 volts to 10.5 amps will flow. The flow will
primarily be to the load.
If you by chance get a bad cell, or a bad connection, you will see problem
as the peak charger will not work, either at all or you will get a voltage
runaway.
Granted a pack could fail at the worst moment. Chances are very unlikely. If
you took a brand new alkaline, and measured its voltage and it showed good,
when was the last time you saw one fail? It could happen, not too often.
well if you peak a pack, it is a pretty reliable thing. You can run a
capacity test on it once in a while, better yet run the fuel pump on it once
in a while on the ground for 3/4C.
Ron Parigoris
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