ThunderDragonCy

Re-arranging the cells in 8.4V NiMH to help fitting in the buggy. Anyone got any experience?

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Evening all.

Thought occurred to me: If I could move the extra cell on a hump pack 8.4V NiMH battery from the centre to the end, it would fit in my DT03 buggy which might be a giggle. Don't want Lipo or any of the associated hassles, but if I could cut open the pack and move the extra cell then I could get a bit more pep in my Grasshopper 3. Anyone done this? Any advice?

Cheers!

 

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really good soldering iron with a good sized tip to melt the solder quickly to separate the cells from the pack, and use flux to join it back up so you get a quick join that's not going to turn into a dry solder joint.

nimh's can handle a bit of heat, but sitting the iron on them for to long will damage them.

this isn't something I'd consider doing myself, I would consider paying someone else that does a lot of work with electronics to do it, but more than likely, I wouldn't use the battery

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31 minutes ago, Darat76 said:

really good soldering iron with a good sized tip to melt the solder quickly to separate the cells from the pack, and use flux to join it back up so you get a quick join that's not going to turn into a dry solder joint.

nimh's can handle a bit of heat, but sitting the iron on them for to long will damage them.

this isn't something I'd consider doing myself, I would consider paying someone else that does a lot of work with electronics to do it, but more than likely, I wouldn't use the battery

Nice one. As it turns out Overlander will build be an 8.4V hump pack with the centre cell moved to clear the DT03 chassis. What I don't know is if the TBLE-02S ESC in the car will run 8.4V. Got a bit nervous of this now as the Bigwig ReRe isn't supplied with an ESC so I wonder if the TBLE-02 isn't up to 8.4V running?

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going out to check on esc settings for your other thread now, will look at the manual I have sitting on my work bench for the tble-02s, but before I do, I pretty sure all tamiya esc's are rated for 7 cell nimh/nicad

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On 11 April 2017 at 3:19 AM, ThunderDragonCy said:

If I could move the extra cell on a hump pack 8.4V NiMH battery from the centre to the end, it would fit in my DT03 buggy which might be a giggle. Don't want Lipo or any of the associated hassles, but if I could cut open the pack and move the extra cell then I could get a bit more pep in my Grasshopper 3. Anyone done this? Any advice?

yeah, 1st thought = "more trouble than it's worth" :lol: even with all the right equipment & experience 

is yours a "ladder pack" (6 side by side cells) with a hump 7th? Vs 2-sticks of 3 plus 7th on top

Factory built 2-stick packs are pretty hard to disassemble generally, they might spotweld on caps instead of tabs as interconnects.

Easier route is trying a Traxxas pack that seems to appear in too many of their RTR sets. If you're in USA dare say they're plentiful & cheap. 

TRX-3908_4.jpg

(Theirs is 2-stick with 7th across end)

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It's re-arranging a hump, and Overlander have already said they can do it for me. Just concerned about ESC performance now. Thinking take one of these:

 

OL-2741_1.jpg

Shift 7th cell towards the lead end, about halfway along the first row of cells and it'll go in my DT03 between the equipment deck and the battery bar.

2017-04-03_08-30-33

 

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1 minute ago, Darat76 said:

tble-02s rated 6.6 to 7.2v

Yeah, read that, but with people using at least 2S Lipo on these I wondered if it would take the extra juice of a higher volt NiMH pack. Perhaps not. Might get another one of those cheap 120A ones I've ordered for the Thunder Dragon if it turns out to be any good.

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6 cell nimh at peak charge is 9v, 2s lipo is 8.4, nominal of nimh is 7.2, nominal of lipo is 7.4, peak of 7 cell is 10.5, and nominal of 8.4.

I recall the older tamiya esc's being able to handle a 7 cell nimh/nicad but not sure if the tble will take it

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Don't forget 7c Nimh is like 200g heavier than a lipo.

Lipo also doesn't drop its volts as much under times heavy drain, car feels more "punchy" 

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54 minutes ago, WillyChang said:

Don't forget 7c Nimh is like 200g heavier than a lipo.

Lipo also doesn't drop its volts as much under times heavy drain, car feels more "punchy" 

I know lipo is better in lots of ways but I have chargers and loads of packs in NIMH so I am happy enough. Just a whim this really. I realised I could fit a 8.4 so why wouldn't I? 😃

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I'm still searching for brands of stickpacks which aren't over-long.

yeah have accumulated dozens of Nimh chargers :) including four Novak Millenium Pro units, best Nimh charger they ever made B)

in comparison, only got ONE lipo capable charger, lives on on the workbench. Runs off AC or DC, does all the batts I use one by one.

oh ok, there's a pocket charger too that lives in pitbox. Just for backup.

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It's an easy enough job to do and would recommend you do this if you don't want to go to lipo as the running difference between 7.2 and 8.4 is significant.

Make sure you've got a good soldering iron, leaded silver solder and a gel type flux.  Don't forget to clean off after as the flux is corrosive.

Would be interested in knowing the v value of a freshly charged 2s compared to 8.4(7 cells).

 

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@M 800STD fully charged 2s lipo is 8.4v with no drop once charged, 7s nimh fully charged is 10.5v with voltage drop as soon as the charger cuts out, how fast the voltage drops to nominal depends on how old the battery is, and how often it's been cycled in it's life, the voltage drop will continue until it's getting close to it's nominal voltage level of 8.4, again the age of the battery determines this point

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35 minutes ago, M 800STD said:

Would be interested in knowing the v value of a freshly charged 2s compared to 8.4(7 cells).

I sometimes run a voltmeter across the pack whilst charging, to check charger's calibration.

There is big difference between lipo & nickels.

6c goes up to 9.6-11V whilst on charger, 7c hits about 11-13V before peak (packs go higher voltage as they age). But once off the charger, let them rest unused & they fall back to about 1.25V/c or around 7.6V & 11V respectively.

lipo otoh, 2s charges up to 8.4V... disconnect charger AND IT STAYS 8.4V :o come back tomorrow and it's still 8.4V.

 

Methink one of the biggest factors of 7c unpopularity BiTD was that it was impossible for old DC chargers that ran off 12V car battery to properly peak a 7c pack. Slightly better if you ran them off a 13.8V powersupply or if alternator is generating, but a stationary 12V leadacid will only do 6c. 

To get around this field limitation... we built 7th into an inline harness, plug that between 6c stickpack and the MSC. Charge stickpack normally; the single subC gets charged separately using the "glowplug" port some chargers had BiTD.

Which is probably an easier solution to OP's Q above, rather than reconfiguring an existing pack.

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Thanks for the info guys.

 

Yes BiTD it was difficult in charging 7c, lack of 8.4 chargers.  Back then chargers were overnight or timer chargers which had no detection.

Also many moons ago, Bigwig era,  there were only a few chassis which accepted the 8.4 packs.

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Hotshot & Boomerang chassis have alternate wider mounting holes for the battery retainer bars, they'll take a 7c flat pack.

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I know you said you didn't want to go Lipo but if all you're after is some speed then a 3S lipo around 2-3000mah will fit in your battery space and be a lot less hassle than messing about soldering NiMh cells. You would probably need to change your ESC though. Hobbywing 1060 ESC's are great, cheap, waterproof and will take 2 or 3S lipos

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