12v batt

[Twisted]

how many charges are 12v batt good for charging lipos, before having to charge it back up?

i would buy a psu for my charger but if i spend any more money this month the one that shall not be named will kick me out lol

[Mart61]

It would depend entirely on the capacity of both the 12V battery and the lipos being charged.

What 12v do you have and what lipos are you looking to charge?

[JeromeF]

how many charges are 12v batt good for charging lipos, before having to charge it back up?

i would buy a psu for my charger but if i spend any more money this month the one that shall not be named will kick me out lol

If you can get away with £15 you could get yourself a 5amp switch mode PSU off eBay

[gazza]

I bought a 110AH Leisure battery from Halfords and it used to charge my 6S Trex 600 Lipos all day at 2C or 10 amps.
These batteries are purpose designed to be discharge cycled hence they can be used. Not cheap at £80 but well worth it for the field in my opinion.
Car batteries aren't designed for this and will soon degrade.
You would probably be able to charge 3S Lipos 7 or 8 times at 2.5 to 3 amps from a car battery before the charger cannot see it anymore due to the undervolt circuitry kicking in.
repeated charging and discharging of a car battery will quickly kill it.
(I've done it)

[GravityKills]

In theory:
- Capacity * voltage (car battery)
equals
- pack capacity * pack voltage * number of LiPos

For example, with a 12 V 44 Ah car battery and 3s 2200 mAh LiPos, don't expect more than 20 charges. In reality it will be less. Take it as a "ballpark number" only.

PS if no pocket calculator is at hand, google will do :-)
PPS I can jump-start my car from a 450 flight pack kids don't try this at home

[Twisted]

the batt is= Yuasa NP7-12
and lipos twister are 11.1v 1000mAh
and hk450 11.1v 2150mAh

[GravityKills]

uh-oh
it has only 7 Ah
means about three charges for the hk450, or seven for the twister.

[xygax]

ONE and a half!

a 12 v 7 is a bit tiny....

The maths was explaned above but i have the following addition...

say you have a 100Ah car battery that will give 10A for 10 H until discharged. now abttery efficency isnt a stright line so you wont get 100A for 1H it will be about 40 mins due to the battery efficency at short discharge periods....

so you need to hnow the Watt hours of the battery to start with
thats 100Ah x 12V or 1200Wh
or 7Ah x 12V or 84Wh
and the same for the battery you want to charge...

for a 3S 2200mAh or 2.2Ah x 11.1V or 25 Wh then multiply by 1.2 for the conversion efficency of the charger say 29Wh

the 100Ah battery will recharge a 3S 2200mA pack 41 times on one charge
the 7 Ah will recharge a 3S pack 2.8 times say twice when you allow for the short time discharge on the small capacity battery.....

Need to get a bigga battery !

[GravityKills]

LOL copper losses will scale with room temperature and the gravitational influence of the moon
I said it's a ballpark number
Most people don't discharge their LiPos 100 %, so I hope it's in the right ballpark. Give or take some.

[Kwickkwack]

Important to note what Gazza said
Get a leisure Battery not an automotive battery. Even better to get a Gel leisure battery, as we have found these to last better than lead acid. however they are even more expensive.

[unwind-protect]

For what it's worth... some empirical data!

My sealed lead acid battery is marked "7Ah", and I have got 4 charges of 2100mAh 3S lipos out of it in the past. The packs were not discharged more than 80%, probably closer to 1500mAh than 1700.

[Twisted]

well its done today 2 twisters and 1 hk450 packs. no problem will get a psu as soon as poss.