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Author Topic: Lipo what to look for.  (Read 1949 times)

cos918

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Lipo what to look for.
« on: May 04, 2010, 10:04:51 pm »

Hi All
Need some advice. I am thinking of using a 7.4 lipo battery in one of my models were weight is a problem. I have been looking at Ebay and seen many diffrent batterys. I am looking around the 400mah mark as they weigh less than 30g.
Some I have seen have only 1 set of wires red/black other's have this and a 3wire harness .There are tones of diffrent makes. Any advice on what to look out for would be apricatd as I have  idea on these type of batterys.
Also what sort of charger should I use.
John 
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red181

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Re: Lipo what to look for.
« Reply #1 on: May 04, 2010, 10:51:54 pm »

John, the lipo's with the extra 3 wires are the ones to go for, this is a balancing lead with plug. When charging a lipo it has to be a dedicated lipo charger, normal chargers will not work. Get a charger with a balancing feature, you plug the balance lead in when charging, and the charger balances the cells, 7.4v is 2 cells, therefore both cells are equal, which is quite important with a lipo battery. Do not overcharge ( a reasonable charger will stop this) and very importantly do not over discharge a lipo, if over discharged they rarely work again, by memory I think 3.2v is regarded as the time to stop!

I use lipos, and have a reasonably cheap balancing charger, Imax B5, its ok, but cannot cycle the cells, I have to do that manually.  Watch out for the "c" rating, if your boat needs a lot of umph, low "c" rating will not cope with the demand. 400mah is not very big, what boat is it, then maybe more specific advice will be given on the type of lipo. Have you thought about 2/3 sub c cells, require less attention than lipo, light in weight, no need for specific lipo charger, and can be run dead flat. Lipo tends to be used for fast boats, that require short run times  :-))
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cos918

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Re: Lipo what to look for.
« Reply #2 on: May 05, 2010, 06:07:31 pm »

Hi
Thank you for the reply.
The motors pull about 16 m A no load each and 20 ma on load. So a 400mah battery should be ok. The reason I want to use lipo is they weigh not a lot compared to NI MH and in my model Finnjet weight is a problem every gram I can save is a bonus.
Looking at  Ebay there are many diffrent makes for China not sure what is good and what is not? any advice here would be welcome.

John
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poddy

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Re: Lipo what to look for.
« Reply #3 on: May 05, 2010, 06:54:48 pm »

Hi John

Have you looked at Giant Cod? I've not used them yet myself, but I have heard good reports. Their stuff is in Bristol.

Something like this perhaps?

http://www.giantcod.co.uk/charge-loong-tipple-2s1p-20c30c-lipo-battery-p-404351.html

Sadly I can't advise about Lipo's. I know nothing about them yet. Good luck.

Pete
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andyn

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Re: Lipo what to look for.
« Reply #4 on: May 05, 2010, 11:26:13 pm »

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red181

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Re: Lipo what to look for.
« Reply #5 on: May 07, 2010, 06:17:41 pm »

Hi John, Agree with Andy, Hobbyking have a massive choice, I use go-market myself. Cant help thinking 400mah will be too small, your stated amp draw on the motor looks very low, have you got a link to it? Is the boat a fast set up or not?

Sub 1000 mah lipo tends to be used a lot on very light micro helicopters, and planes, and the run time is generally 8 mins or so. If you imagine they are more efficient with less amp draw (no water to move, just air) have a big gear ratio, and small brushed motors, such as in the esky lama coaxial, these have minimum 1000mah lipo, and some slightly larger or heavier such as the twister skylift chinook runs a 3 cell lipo.

I have just finished a jet boat project for me and sons. I tried a 1500mah 30c 3 cell lipo, it struggled a bit, now running 2300mah 3 cell 30c, run time is 10 mins. I will in the next few days fit an amp meter for you. it might help with your decision.

Paul
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