Car battery concerns...

[bencook]

I'm going away next weekend and hope to get in quite a bit of flying time. I plan on charging my 3S 1800mAh batteries from my car battery, but I'm concerned about ending up with a flat (car) battery...

I think the car battery is about 45Ah.

So assuming I charge at 1C (1.8A) that means I'll be drawing around 1.8A for an hour from the car battery (as the car battery and heli battery are roughly the same voltage). So if I were to charge, say, 10 batteries I'll have used 18Ah, meaning I'll still be able to start the car??!!

I'm guessing that in reality the car battery holds less than 45Ah, and due to inefficiencies in the charger that it draws more than 1.8A during a charge. The question is, how many batteries can I charge ensuring I don't drain the car battery...

[marktigere1]

Car batteries don't like being drained too far as they are designed for standby use. Unlike boat/caravan lesiure batteries which are designed for deep cycling.

I would have thought you would be fine though and maybe if you started the car after say 5 charges you would be okay.

Belt and braces and all that.

Cheers

Mark

[David Drew]

Beware!!!

A guy at our field was using his car battery to charge equipment. When he drove off the field his car caught fire

Maybe had nothing to do with using the car battery - but also may have been a result. We'll probably never know, but what we do know is that he will never do it again.

For the sake of £50/60 a leisure battery is well worth it.

david

[moyesboy]

Thats wierd and probably unrelated.

If you used the car fag lighter socket for charging and pulled too much current and it didn't have the right fuse in line (the lighter plug should have a fuse in it), then the wiring to the socket in the car could overheat and damage the insulation, then short as you drive off over the rough field.

If you were disconnecting the battery terminals to connect, and made a bitch job of connecting them again - or you damaged the insulation to the positive under the bonnet with your croc clips - then you could have a short and a fire as result.

Yuo might also stick your flight box in the back of the car and have some didgy wiringon the way out to your leasure battery, and have that short and sert fire to your car
or one of your lipos short and set fire to your car as you go over a bump.

I really don't think you are increasing fire risk charging from your car!

Regarding how much charge you can pull:
Some woman drove into my terrano and while it is being fixed on her insurance, they are paying to rent me a toyota Landcruiser "like vehicle", and I was suprised to find under the bonnet two massive 12v batteries. So anyone who is worried about charging their trex600s should just send them to me for charging!


seriously I think you pull a whole 1800 lipo out of the car battery every time you start - and the alternator sticks it all back in in 10 minutes of tickover. So no problem really charging 2-3 trex450 batteries.

[gazza]

I flattened my car battery the same way charging my 6S packs at the field.
So, I 'Aquired' a nearly new 225ah Train battery from work

All problems solved Er...Except it takes a week to charge & after lifting it I'm pushing my balls round in a wheelbarrow after every flying day

[Jamez]

Thinking of capacity, your car battey is 45000 mah, your lipo will want about 2000 mah to charge (charger lose's etc), meaning you should be able to charge the lipo about 20 time's and not flatten your car bat to half its capacity in theory anyway. Try it, take a set of jump leads just incase, and let use know

[bencook]

Thanks for all your replies. I'll let you know how I get on...

[SRH990]

Dave,
the car that caught fire was because the driver forgot about the lipo, shut the bonnet and the lipo landed on the exhaust manifold, thats one way to set a lipo off I hadn't thought of!

According to our American cousins, the best 12V source for on the field charging is a Toyota Prius, bit more than a liesure battery or generator though

[David Drew]

Dave,
the car that caught fire was because the driver forgot about the lipo, shut the bonnet and the lipo landed on the exhaust manifold, thats one way to set a lipo off I hadn't thought of!

That sort of explains it Didn't hear the latest!

See you next W/E I hope.

David