bugsiegel

My Feedback: (2)

what happens if I start my car and then hook up the box battery to the car battery with booster cables?
will I cook the field box battery or will it peak charge it just like a car battery?

larryflew

My Feedback: (13)

First of all wet cells do not "peak" charge. Now for the other end-you are basically using a charger (alternator) that is set up to charge a 700+ ah battery and trying to charge a 7 ah battery with it. It will be reading both batteries and their charging needs (probably in actuality it won't even notice the little guy) and charging at the rate called for by the voltage regulator which will be way above the rate needed for the smaller battery. Good way to boil away your small battery. Have never had to actually field charge my flight box, but if I did have to I would use a DC type charger like my alpha 4 or Tekin to make sure it is not being overcharged. You might also try it with the car turned off as I doubt your little batter would draw the car battery down enough to create any start problems.

flatfour

My Feedback: (8)

No, lead-acids do not peak charge. But the charge can be controlled by measuring the current consumed when a constant voltage applies. Have a look at the links. I have 2 Battery Tenders for my motorcycles. The best part is to just plug em in and forget about it.

http://www.batterytender.com/algorithmplus.html#3

If you consider getting one for the flight box, I would suggest the junior model. They can be found at most motorcycle web sites.

http://www.batterytender.com/batterytenderjunior.html

ftomteen4cat

I just dial my bench power supply up to 13.8V and hook my gel cell up to it. That gives it a constant-voltage, or what I've heard some people refer to as a 'taper charge', meaning the current drops off as the battery comes up. When the current drops down to 30mA or so, I disconnect it.

My question is, how is this different than plugging it into a cigarette lighter in your car? I thought the amount of current you drew was dependent on the size of the plates in the battery. I'm no battery expert, but to me 13.8V is 13.8V, regardless of how much you can source.

martyg

My Feedback: (42)

So, is there a gismo I can build/buy to charge my field box gel cell while driving out to the field?

dickie3126

I have to agree on the previous post on the "Battery Tender". It's been a good addition to my stuff. I just plug it into the flight box and forget about it. Just my 2 cents.

Dickie

Jazzy

I remember seeing a similar thread some time ago... Maybe it was quite some time ago... Anyway, from what I remember several people who wanted to 'top off' their field batteries would attach them to their auto's charging system for the short trip, (less than 30min.), to the flying field.
The way I understood it this was an acceptable means of charging but not highly recommended.
An auto's alternator will not overcharge it's own battery. As the battery's voltage rises the output current of the alternator decreases. The more accessories you run, IE. lights, fan, AC, etc., the more the battery and subsequently the alternator will put out to keep up with demand. This goes into constant voltage vs. constant current. With constant current the voltage varies to maintain the current while with constant voltage the current decreases the closer the battery's voltage gets to the supplied voltage, (tapering charge).
I may not have all the facts perfect but, I think its close enough.
So, yes, one could hook up the field box battery to the auto's system for an occasional charge if one forgot to charge it at home the night before.

Well, I just got back from my truck and the findings are good. Curiosity got the best of me.
With a 7AH gel cell and my ammeter this is what I got:
Voltage of auto w/engine running @2K RPM...14.42V
Voltage of field battery - open........................12.67V
Current to field battery initially.........................0.9A
After only a minute or two.............................~0.2A
Field battery ending Voltage..........................13.13V

The way I see it 200mA is just right.

There are of course high output alternators...