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Author Topic: NiMh - Lipo ?  (Read 2165 times)

John Mk2

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NiMh - Lipo ?
« on: August 25, 2010, 11:22:39 AM »

Hi All got a bit of a snag {:-{     Got a HOR App/Cat 32in 2771kv motor & 125amp Suppo E.S.C got program sheet.   First run useing 14 cells (G.P 3300mah) fully cycled & charged up (19.8volts)
Not great >:-o Power tailed off after about 3mins  no cut off just slower & slower everything hardly warm    {:-{ So i must have programed the e.s.c for NiMhs O.K :-))  Anyone know if it would be o.k to fool the e.s.c in to its useing Lipo 3s to get more power from the NiMhs & Avoid low voltage shut down ? Or will i blow something up :embarrassed:  Thanks in advance ok2
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #1 on: August 25, 2010, 11:31:02 AM »

you can normally select lipo cut off when you program it how old are the nicads ?if they where not all bought and used as one pack you may find some off them are going off at the end off a run you should be able to check each cell for voltage, they should all be very close the number does not matter it is how close they are (thats why you hear about matched cells) if one or two are lower that will kill the pack as they will go flat first and the pack will loose it's performance.

peter
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John Mk2

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Re: NiMh - Lipo ?
« Reply #2 on: August 25, 2010, 11:40:45 AM »

Almost new only used 3-4 times & well looked after :-)) Also useing 4mm silicon wire all round!
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #3 on: August 25, 2010, 02:06:54 PM »

are they all from the same batch and age  also still check voltage off individual cells i have seen new packs with bad cells it then pulls all the other cells down.

Peter
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John Mk2

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Re: NiMh - Lipo ?
« Reply #4 on: August 25, 2010, 02:25:28 PM »

All the cells are soldered useing brass bar by a  Fast Leccy /O.M.R.A Man  ok2 You Might know him K.B ?  So will be a bitch to take apart & check each cell :((
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #5 on: August 25, 2010, 04:48:01 PM »

you don't have to take them apart just use two pins the top button + is connected to the next cell - so if you stick a pin through the heat shrink you get a - on the cell it is touching and a positive on the cell before the first and the last cell can be checked via one lead and a pin once you have done it once it is easy.

the thing about good cells is this they should give an even voltage till they reach a point where they just go flat they should not do it gradually they should just dump at the end.

How are you charging them if you don't charge them with high enough amps they will not give it up at a high rate.
look at the graph it shows how a average pack will give up its power  a good pack would have them all together at the end
peter
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John Mk2

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Re: NiMh - Lipo ?
« Reply #6 on: August 25, 2010, 05:01:00 PM »

We live & learn :-)) Useing a Imax B6 (Jack of all trades) Will follow your advice & give it another go :-)) Again Thanks for the help!
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Tombsy

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Re: NiMh - Lipo ?
« Reply #7 on: August 25, 2010, 06:05:49 PM »

I think your going to have a hard time supplying enough amps with NIMH batteries. My UL-1 with a 60amp esc needs a 60 amp average and the boat is a lot smaller than yours.
Multiply the mah x current (C) gives you the amps.
3200mah lipo 20c battery would be 3.2 x 20 = 64 amps (minimum for my boat)
I doubt your NIMH's are putting out 20C

Put a couple of these in your boat and watch out! They made my boat a rocket. (50mph)
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10305

Your charger will work perfectly with them charge at 4 or 5 amps.
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John Mk2

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Re: NiMh - Lipo ?
« Reply #8 on: August 25, 2010, 07:35:30 PM »

Hi I used to run Lipos 3s/4s in fast leccys last year. Then went scale so sold them all to fund it {:-{ Got Lipo 4s on order (4000 35c) I just wondering why the Nimh where no good at all :((
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #9 on: August 25, 2010, 09:48:06 PM »

we got some lipoes from hobby king and all I would say is go on the forum and have a read BEFOR you buy  or PM red181 and ask him,there C rating is not the same as others look at overlander they are a bit dearer but you get what you ordered and they can be returned.
as for the c rating of nicads there are no published C ratings for them but back to back test with nicads good nicads will give there power up better than hobby king batteries.
what charging rate did you use on you batteries how many amps ?

Peter
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John Mk2

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Re: NiMh - Lipo ?
« Reply #10 on: August 25, 2010, 10:06:00 PM »

3amp charge for fast charge. 1 amp for slow. Both ended on peak charge alarm.
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #11 on: August 25, 2010, 10:33:58 PM »

I would charge a min of 3 amp and only just before I you run them the night be for is no Good nor is slow charging if you want to get the max out.

Peter
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John Mk2

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Re: NiMh - Lipo ?
« Reply #12 on: August 25, 2010, 10:42:13 PM »

I will do that until i get the Lipos
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Tombsy

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Re: NiMh - Lipo ?
« Reply #13 on: August 25, 2010, 10:50:38 PM »

we got some lipoes from hobby king and all I would say is go on the forum and have a read BEFOR you buy  or PM red181 and ask him,there C rating is not the same as others look at overlander they are a bit dearer but you get what you ordered and they can be returned.
as for the c rating of nicads there are no published C ratings for them but back to back test with nicads good nicads will give there power up better than hobby king batteries.
what charging rate did you use on you batteries how many amps ?

Peter
I've had no problems at all with my Hobby King packs and they easily have 5mph on my brand name $120.00 packs. (Shumacher, CommonSense R/C)
Whatever the C rating is it sure works for me.

If you want your nimh's up to snuff peak them again at 5 amps right before you launch.
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HS93 (RIP)

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Re: NiMh - Lipo ?
« Reply #14 on: August 25, 2010, 11:05:57 PM »

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