Nicad vs Nimh for electric start

Batteries, Chargers, and Battery Management Systems.
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adamjedgar   10 µW

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Nicad vs Nimh for electric start

Post by adamjedgar » Aug 09 2019 4:32am

Hi guys,
I have a powered paragliders with a 200cc 2 stroke single cylinder engine.
The unit uses a 16.8 volt system and has 14 Nicads (sub C 1700mah)
It is electric start and also charged the Nicad batteries whilst motor is running.

The existing batteries are soldered together in series, however after about 130 hours they have developed a memory And cycling them has not worked (perhaps I should have done this more often).

I decided to change over to Nimh batteries (3300mah sub C).

After making up the battery pack, charging batteries, and installing into paramotor, it barely turns the motor over.

I am not sure but I have another paramotor with a 12 volt lithium battery...an auto electrician said they draw a lot of amperage when starting.

How can I determine how many amps the paramotor electric starter needs from batteries when cranking?

Has anyone any experience with Nimh vs Nicad for this kind of application?

Do I have to go back to Nicads for electric start use?

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Drunkskunk   100 GW

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Re: Nicad vs Nimh for electric start

Post by Drunkskunk » Aug 09 2019 12:06pm

A manufacturer of aircraft grade parts will have published the peak amp draw for the starter motor.

Likely the NiMh cells had a lower C rating than the NiCads, and couldn't handle the amps. You don't need to switch to NiCads, you just need to find cells with the same peak amp specs as the NiCads you had.
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adamjedgar   10 µW

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Re: Nicad vs Nimh for electric start

Post by adamjedgar » Aug 09 2019 12:34pm

Not aircraft grade, Paramotors are not certified aircraft grade in any way shape or form. These are just stock standard 2 stroke engines.

How do determine the C rating and peak amp capability for a Nimh battery when purchasing it?

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fechter   100 GW

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Re: Nicad vs Nimh for electric start

Post by fechter » Aug 09 2019 12:52pm

adamjedgar wrote:
Aug 09 2019 12:34pm

How do determine the C rating and peak amp capability for a Nimh battery when purchasing it?
That might be hard without testing a sample yourself. I don't often see discharge current ratings for these kind of cells.
To measure the current, you need some kind of ammeter in series with the pack.
Here's an example:
https://www.amazon.com/RC-Electronics-I ... B001B6N2WK

In general, NiCd batteries can source more current than the same size Nimh, but it's all over the map depending on the manufacturer.

Going to a Lipo battery would give great starting current and be much lighter, but the charging system would most likely need to be changed.
"One test is worth a thousand opinions"

adamjedgar   10 µW

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Re: Nicad vs Nimh for electric start

Post by adamjedgar » Aug 09 2019 1:33pm

Here are the specs for the batteries I purchased.
According to Jaycar electronics they are supposed to be able to handle a discharge rate of more than 40 amps.

Either I have done something drastically wrong or these specs are not accurate?

https://www.jaycar.com.au/1-2v-high-dis ... y/p/SB1611

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fechter   100 GW

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Re: Nicad vs Nimh for electric start

Post by fechter » Aug 09 2019 1:48pm

adamjedgar wrote:
Aug 09 2019 1:33pm
Either I have done something drastically wrong or these specs are not accurate?

https://www.jaycar.com.au/1-2v-high-dis ... y/p/SB1611
Seems like those should work. I would not be surprised if the specs are exaggerated.
I would try measuring the pack voltage at rest and when cranking to see how much the voltage sags.
You could also try measuring individual cells when cranking to see if they are even or if one cell is bad.
"One test is worth a thousand opinions"

flat tire   1 MW

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Re: Nicad vs Nimh for electric start

Post by flat tire » Aug 09 2019 2:01pm

Don't smoke crack or use those chemistries. Go lithium.

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Toorbough ULL-Zeveigh   100 MW

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Re: Nicad vs Nimh for electric start

Post by Toorbough ULL-Zeveigh » Aug 09 2019 2:25pm

are you at all familiar with the CF-104 widowmaker (aka lawn dart)?
a good percentage of the crashes were traced to the NiCd starter batteries going into thermal runaway at random & blowing a hole out the side of the fuselage.
investigation determined that the failures all occured only with battery packs more than 30 months old.
consequently a maintenance directive was issued requiring mandatory fleet wide starter battery replacement every 2 years regardless of condition.
with a dumpster full of lo-mileage subC cells to choose from, i had a lifetime supply of batteries for my r/c cars.
Kick down the barricades Listen what the kids say.
From time to time people change their minds But the Frock is here to stay.
I've seen it all from the bottom to the top Everywhere I go the kids wanna Frock.
Around the world or around the block Everywhere I go the kids wanna Frock.

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Drunkskunk   100 GW

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Re: Nicad vs Nimh for electric start

Post by Drunkskunk » Aug 09 2019 2:58pm

That 40A probably isn't enough. I would guess it needs to be closer to 100 amps. If you know the name brand motor, they probably have a recommended battery. or if it's a snowmobile motor, you may be able to look up the Cranking amps of the battery specified for that snowmobile
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adamjedgar   10 µW

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Re: Nicad vs Nimh for electric start

Post by adamjedgar » Aug 09 2019 5:20pm

thanks guys,
i might start with the starter motor specs...i will pull that off the motor and try to see what cranking amperage it draws. From there i can work backwards to a battery solution.

just as a slightly off topic question, would adding a second 16.8V battery pack in "parrallel" improve the cranking capacity? (i dont intend doing this, just wondering)

p.s. love the story about the widowmaker aircraft. I have some RC aircraft (including a 4 engine C130 Herc with a 100" wingspan powered by OS FS52 4 stroke engines. It has only flown twice in 10 years because its difficult to keep all 4 engines running...electric would be a much better option)

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Drunkskunk   100 GW

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Re: Nicad vs Nimh for electric start

Post by Drunkskunk » Aug 09 2019 6:21pm

Yep, you parallel 2 identical packs, you double maximum amps.

Yeah, once you start flying Electric planes, your gas planes will collect a lot of dust.
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fechter   100 GW

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Re: Nicad vs Nimh for electric start

Post by fechter » Aug 09 2019 7:15pm

Nickel chemistry cells don't play nice in parallel. When charging, terminal voltage drops at end of charge and one string can start drawing from the other and go into thermal runaway.
"One test is worth a thousand opinions"

Punx0r   100 GW

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Re: Nicad vs Nimh for electric start

Post by Punx0r » Aug 10 2019 7:34am

Why not use A123 26650 LiFePo4 cells? 4S is a popular drop-in replacement for 12V starting batteries. They long-lived, high quality and out out lots of amps.

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Re: Nicad vs Nimh for electric start

Post by adamjedgar » Aug 14 2019 4:19pm

fechter wrote:
Aug 09 2019 7:15pm
Nickel chemistry cells don't play nice in parallel. When charging, terminal voltage drops at end of charge and one string can start drawing from the other and go into thermal runaway.
Doh...damn cause after being suckered in by my local Battery World yesterday, who assured me the pack I made was crap soldering and crap batteries and that they could make a suitable pack for this...I am now left with 2 new Nimh battery packs that individually barely turn the motor over...and a wallet with a $350 hole in it!

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spinningmagnets   100 GW

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Re: Nicad vs Nimh for electric start

Post by spinningmagnets » Aug 14 2019 5:09pm

You might add super-capacitors for the starting, and parallel them with the NiMH (isolated by a push-button switch with a current-limiting resistor), because caps bleed down. (edit: I agree with Fechter, avoid NiMH/Nicad...I would recommend LiFePO4 + supercaps)

Super-caps last many thousands of cycles, and also work well in extreme cold.

A common four-cylinder car has been recorded as drawing 200A for a split second to get the engine turning over, and 100A continuous to keep it spinning until start.

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fechter   100 GW

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Re: Nicad vs Nimh for electric start

Post by fechter » Aug 15 2019 12:02am

adamjedgar wrote:
Aug 14 2019 4:19pm
Doh...damn cause after being suckered in by my local Battery World yesterday, who assured me the pack I made was crap soldering and crap batteries and that they could make a suitable pack for this...I am now left with 2 new Nimh battery packs that individually barely turn the motor over...and a wallet with a $350 hole in it!
Dang, that's a lot of money for a little battery pack. Bummer.
It's no problem to parallel them for discharge and if the strings are long enough they might be ok for charging. You could try them in parallel to see how it cranks. The charging issue might be solved with some circuitry.
"One test is worth a thousand opinions"

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flippy   1 MW

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Re: Nicad vs Nimh for electric start

Post by flippy » Aug 15 2019 6:35am

we need to start at the basics here.

can you show us the charging electrics on the motor and do you have specs on the power generation?
Lithium beats liquid dinosaurs.

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thunderheart   100 W

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Re: Nicad vs Nimh for electric start

Post by thunderheart » Aug 15 2019 1:30pm

Punx0r wrote:
Aug 10 2019 7:34am
Why not use A123 26650 LiFePo4 cells? 4S is a popular drop-in replacement for 12V starting batteries. They long-lived, high quality and out out lots of amps.
You read my thoughts!!! High-drain LiFePO4 cells like A123 ANR26650M1B (my test) or QB26650-2500 (my test) are ideal for starter batteries. Plus, they do in large range of temperatures (-20 - 45*C if i'm not mistaken).
Yinlong LTO Lithium Titanate safety tests: https://youtu.be/eAUYbSDEy6I
Toshiba SCiB LTO Lithium Titanate safety tests:https://youtu.be/XsrRDZxEFQE

LG M50 vs Samsung 48G:https://youtu.be/KGJDogOG4zw
LiFePO4: QB26650 2500mAh 50A vs A123 ANR26650M1B: https://youtu.be/GOSkte11lRc

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