a question about charging li-po batteries

[frank carlisle]

i've run my car battery dead twice now while charging my pq 3700 bats. charging one battery off the car battery is fine, but the second charge doesn't even last long enough to charge the li-po before the car battery goes dead.
has anyone else had this problem?
does anybody have any ideas about a more efficient charging method at a location where ac is unavailable.

[Alan Hahn]

I believe a new, fresh charged auto battery should be able to discharge at 25 amps for about 100 minutes. Assuming your charger is working at 100% efficiency (which I doubt), you would need ~6 A for a 1 hr charge (or 3 A for 2 hrs). It would seem to me that your car battery may not be the newest, altho it might be fine for the car for some time more. Also your car may be keeping a drain on the battery that you are not aware of. I always turn off the indoor lights when I go to a contest, since I often leave the car door open. I have had a problem of no juice at the end of a day (that was a pretty poor auto battery in that case). Anyway, maybe the best idea is to buy a deep discharge marine battery for this job. Doesn't really cost any more than another Li-Poly Pack. Main disadvantage is having to charge it before going to the field, and hauling it around.

I am guessing this is one of the main disadvantages of electric. With the cost of Li-Poly batteries as they are, it is a financial effort to keep the equivalent of a gallon of $14 Sig fuel on tap.

[frank carlisle]

alan,

i'm looking at getting a new car battery. the one in my car is 6 years old. i can get one 63 minute 3 amp charge out of it. if i try a second one the car goes dead.
i'm using a brand new multiplex multi charger. and i don't know if it's 100%.
lugging a marine battery around is not an attractive idea. nor is running the car for an hour while the bat charges.

i think maybe heading to the field with four fully charged batteries is a plan.

the charging problem really is a downside to the e-power thing. and i'd have never thought about it if the car hadn't gone dead. what a way to learn.

here is a question--how many li-po charges could you get out of a marine battery?

[Alan Hahn]

I can't say about the marine battery for the number of charges, but its main attribute is that you can really suck most of the charge out of it without damaging the battery. You really shouldn't run a car battery down all the way--it isn't made for deep discharges---the individual cells can reverse---just like in a LiPoly. Here is a link on lead-acid batteries I found through Google

http://www.uuhome.de/william.darden/

If you have had that car battery for 6 years, it has already given you its best. Probably time to replace it anyway. Just get a new battery which has not only good Cold Cranking Capacity, but also a big Reserve Capacity. This latter quantity is what tells you how long it will discharge at 25 amps.

I think showing up at the field with everything pre-charged is smart too. My charger (Astro 109) recommends charging LiPoly at 1C, so that means an hour of charging. Also need to include cooling off time. Just noticed my CellPro pack recommends the same. I decided to learn my electric using the new Sig E-Force Arf RC, thought it might be a little cheaper than going CL first.

[Igor Burger]

I use to do little trick - I start the car engine for few minutes - it refreshs empty battery very quickly (charging at constant volatage). ... just be sure that rpm is enough to have at least 14.5V on battery.

[frank carlisle]

i thank everybody for the info.
this is my first excursion into electric c/l. and it's been quite a learning experience.
the first thing i learned is that if you get a shopping list from someone that already has a working model, you don't need to know what you're doing. all the components come with clear instructions and there are only a few wires to connect.
the second thing i learned is that everyone wants to see the airplane go. and this is the point at which you have to start learning about what you are doing. i had to get jump starts twice after charging batteries. so the first thing to do is have enough energy to put up those demo flights. in my case this means. get a new battery for the car, carry jumper cables and two li-po batteries just are'nt enough. charge everything at home on an ac to dc power supply so as to have a head start at the field.
i spent $772.95 getting this plane going and it was a good investment. i see definite advantages in electric vs. glow power that more than compensate for the initial start up costs. the reliability being a major factor. then there is ease of operation. next we have a much more earth friendly model. no spilled fuel, no noise and no fumes.
it will take about 2 or 3 years for me to make a total conversion from glow to electric. but that apparently is the direction i'm headed in.
btw-- i took video of everything i did. there are ads in the classified section here for the discs. the funny one is "flying the electric smoothie" it's sort of a blooper video because the plane didn't start the first time i hit the on switch. what a surprise when i popped the hatch off only to discover the battery was still in my pocket.

[Alan Hahn]

Frank,
I don't think you have gone far enough. You should go out and buy a nice RV with a generator. That way you can always keep those batteries charged up!

I bought the Sig E-Force ARF RC, which comes with a brushless motor for ~$150. Then it was another $400 for the support stuff (ESC, 2 LiPo batteries, charger, some smaller RC servo's...). Yes the buy-in cost is pretty steep.

[Ironbomb]

Hey Frank, Alan has a good idea, if you get a RV, not only can you keep your batterys charged, but you will have a place to keep the beer cold. Then I would not have pack ice, I could just drink your beer. The possibilities are endless......

Greg 

[frank carlisle]

you guys are going to run me broke with all this rv talk. it does have it's attraction i must say.

yesterday i was out flying and linda discovered there was a bird in the basement (fell down the chimney i guess) since i wasn't there to rescue her from the bird she called my friend stan. when he asked her what she wanted him to do she said make sure frank's planes are safe.

i realize this has nothing to do with the topic but ....heck.

i'll price out rvs this week and get back to you guys. but don't you think a couple more batteries would be a little more reasonable?

[Dean Pappas]

Hi Frank,
You need a new car battery.
You should be able to charge your 4-cell 3.8 AH pack seven or eight times and still strart the car, reliably.
regards,
Dean Pappas

[frank carlisle]

hi dean,
i'm going to the auto store before my next flying session.

BTW--this electric stuff is great! it's way superior to glow at least in my opinion.