Current RC Battery tech for old cars

[Dan Dubeau]

While moving my Dad across the province this summer I became the recipient of many, many boxes of stuff....some of it mine. In a few of those boxes were my old rc cars, and trucks. A Tamiya blackfoot, and clodbuster, and another one I can't remember the name of. All in various stages of disassembly...... Back when I was a kid we used nicad batteries, and the ones in the boxes are junk, and I can't find the charger for them anyway. Poking around the internet it seems LiPo batteries are all the rage, but not without dangers. There are also NiMH batteries too. NiCad seems to be ancient tech. I'd rather not burn my house down if I can help it, but I'd like to get them going again with my son, and it will give us some projects to work on together. Should I just pick up some regular nicad ones, and a new charger, or get lipo, and get over the fears of fires (overblown?). I'm not looking for outright performance, just good life, usability and above all, safety.

I'd love to just use my Makita 18v batteries, as I'm already well invested into those, but maybe that's a project for a another time. A scratch built 18v monster truck maybe?

Any RC guys here? I probably haven't played with these since I was about 12/13 and mid 90's, I'm sure a lot has changed in the RC world since then.

 

[Darren]

My son has an RC truck. It uses an 8.4v NiMH battery. When i was a kid, my stuff was also NiCad. The NiMH is worlds better. The new LIPO batteries are supposed to be even better, but apparently like to burst into flames. Youre actually supposed to charge them in a special fireproof bag. No thanks...

 

[phaxtris]

Don't bother with nicads, lipos are a world ahead, buy a 2s pack and rig up some kind of low voltage cutoff or buy an esc with low voltage cutoff and your good to go, same size pack probabaly 3x the run time

I think there fire issue is a bit overblown, it has happened, but there are millions of LiPo packs out there...you don't hear of millions of fires

Now that being said it isn't impossible, you can buy those little fire bags for a couple bucks on Amazon, I just charge myne in one of those old metal ammo cans

They are so good nitro doesn't even hold a candle to LiPo/brushless anymore, cars/planes/boats, all way better with lipos

 

[DavidR8]

I had about ten LiPo batteries when I was flying electric planes and never had an issue. I was careful and only charged them outdoors in a metal toolbox that I rigged up with charging leads inside with external connectors for the actual charger. I also drilled a 3/4" hole in the top with a rotating cover. If something went awry I could yank the charger and stick the nozzle of a fire extinguisher in the hole and fill it up. No idea if it would extinguish the fire but it was better than nothing.

 

[Darren]

I didn't think it was a huge issue, but I have been have with the Nimh for now. Just something to be aware of i guess

 

[Dan Dubeau]

After a bit more poking around the internet I think I might go NiMh for these old trucks, and if the RC interest has staying power maybe Lipo for any future higher performance builds. I don't want to have to worry about them mischarging or having any issues playing with them when I'm not around. Plug and play is the best option for them right now, they're only 8/10. I don't want them to have to remember to "put the batteries in the fireproof box outside, and have the fire extiguisher handy" They can barely remember to bring their coats and mitts home from school lol.

I've only got one radio, an old 2ch futaba 2 stick. I'll have to pick up another one, so we can play around together. I can't believe how cheap this stuff is now. I remember huge price tags on this stuff back then. I can see a scratch build in our future.

 

[PeterT]

Hmmm where to begin. My RC career has spanned the battery chemistries from NICD to NIMH through LIPO & other lithium based. Interestingly RC & cordless power tools have followed kind of a loose parallel path. NiCD is not entirely dead but close enough for hobby purposes. The issue has always been environmental (Cadmium). NiMH is better environmentally & has improved energy density on average but has other drawbacks where NICD was actually better. Lithium kicks the stuffing out of both of these on energy density basis, but there are many branches of lithium, Ion, Polymer and even these names mean different things in different applications. If lithium cells are discharged below a threshold voltage they are generally pooched. They hold a lot of energy so if they get crunched or shorted, bad things can happen.

In terms of charging they are all safe & they are all dangerous. The point is use the proper equipment & know what you are doing. The fires you hear about with RC LIPO are real but getting much safer over time. Usually its some permutation of bad charger, bad battery, bad charging practice. But for your average person, no different than any other shop tool in the wrong hands. Personally I think LIPO is as close to plug & play as it ever has been. The packs have balancing plugs (individual wires connected to each cell) so 'good' chargers have all the intelligence to not only charge/discharge/condition properly, but also diagnose potential safety issues long before things can get out of hand. A classic issue is a degrading single cell within a multi-cell pack. If its not within certain voltage levels & thresholds of its neighbor cells, the charger says nope. Vs a classic NIMH RC pack which has no such wiring or intelligence. The charge/discharge algorithm works on the basis of entering cell count & their maH capacity. So it can get tricked if cells are degrading. My 5 year old LIPO charger spits out internal resistance of each cell & other diagnostic capacity information so I can monitor health over time.

The big issue is retrofitting. An RC car has a motor with a defined KV & therefore corresponding operating voltage window. NI cells are multiples of 1.2-ish volts nominal, so for example an 8 cell series pack is 8*1.2=9.6v. Lithium (lets assume polymer) are 3.7v nominal. So 1S=3.7, 2S=7.4, 3S=11.1v. So it may or may not be a direct voltage replacement match (9.6 is in between 7.4 & 11.1v). In reality there is wiggle room on both the motor & actual pack voltage fresh off the vs near depletion.

Hope this helps for now. If you are looking for more specific information maybe I can help. RC cars are not my forte & I know some classes hang onto NIMH for rules reasons vs supporting better chemistries. Even that puzzles me because when I raced F5D (electric pylon) we had on-board watt limiter devices that are the size of a postage stamp & regulate the energy consumed. This is the ultimate playing field leveler, almost exactly analogous to a defined volume of specified fuel which is very common in auto racing events.

Battery Comparison of Energy Density - Cylindrical and Prismatic Cells

This battery comparison chart illustrates the volumetric and gravimetric energy densities based on bare battery cells, such as Li-Polymer, Li-ion, NiMH.

www.epectec.com

 

[Dabbler]

FYI Some NiCd cells can be rejuvenated by an charger that cycles them. I had some WW2 batteries that I rejuvenated back in the late 70s,and they had about 70% of their rated capacity....

My personal preference is NiMH.

 

[Susquatch]

I'm so tempted to add to this thread with a crap load of experience. Instead I'll just second what @PeterT said.

OK, can't resist one small addition. NiCads are prone to damage by reverse charging (this happens when one battery in a stack goes dead before the others) and current tunneling. Best to just avoid them no matter how tempting they might be.

 

[Dan Dubeau]

Thanks for the insight. Appreciate the explanation Peter. I think a couple cheap NiMh and a suitable charger will get us going for now. If either kid shows an interest in it, It'll probably cost me a bunch of money from there....

I know when I was young, I made a bunch of different replacement parts (pretty crudely) with hacksaw and files from acrylic, steel and aluminum, out in my Dads garage. Part of me hopes they take an interest in it, because now we have a pretty well tooled up CNC capable shop in the garage to make all kinds of cool parts I could have only dreamed of when I was a kid. Maybe I'll get to build the big nitro powered monster truck I always wanted. If the kids are interested I mean...

 

[Former Member]

I have had three battery failures in my life time.

1st: 2v Bell Cells (200lb ones), old tendril growth which shorted during charge, top part of battery missing as in gone!

2nd: NiCad short, just melted down.

3rd: Lithium cell from laptop broken, smaller piece went up in flames 4-5ft high. There was no putting it out, it just burned itself out.

All are dangerous, keep it mind as they store energy and when they fail they release it quickly and lots of it.

 

[PeterT]

This is another generic plot to be aware of when discussing battery chemistries. Its a bit of apples & orangs because its showing different capacities on X axis & different nominal voltage on Y. As I mentioned LIPO has nominal of say 3.7, another lithium may be 3.2. Anyways the point is if one could normalize them, lithium have very flat discharge depletion curves relative to NIMH, NICD & alkaline for good measure. Batteries are ever changing & generally improving. Eneloops (a version of NIMH) have good discharge characteristics.

Another important aspect is discharge & charge characteristics, also a function of chemistry. In many applications its important to deliver high current without destroying the cell or giving up a high proportion of its capacity. One can use C-rating as a guide. An average RC LIPo pack these days can do say 50C. So a 5000mah pack can deliver 50*5=250 amps. NIMH are in the order of 5-10, usually much lower like 1-2 if you go by the book. Same goes for charging, getting energy back into cells ca be as important in many applications. Like most things in life, its tradeoffs & cost.

The good news is if you want to play in NIMH space with older vintage RC car or boat or whatever, good quality reliable NI charging equipment is practically being given away as LIPO has dominated the scene the past 20 years.

 

[PeterT]

Now some of this belongs in category of Darwin awards, but just to provide a sense of energy dissipation

 

[Susquatch]

If either kid shows an interest in it, It'll probably cost me a bunch of money from there...

If they do show an interest, doing something like that WITH THEM will be worth every penny of "a bunch more money". Soon they will be grown up and gone. Go for it Dan!

 

[Engmaxx]

Another plus to LiPo is they are much lighter than NiMH/NiCad. You will love the acceleration and top speed performance boost because of this though you may not have a comparison to make. Buy a balance charger with LiPo and you are laughing. Once I converted, I never looked back. I have pulled apart LiPo batteries to replace bad cells with good ones, easy to work on really. You can also 'storage charge' LiPo that can give them years of life to be used again in the future.

 

[Dan Dubeau]

If they do show an interest, doing something like that WITH THEM will be worth every penny of "a bunch more money". Soon they will be grown up and gone. Go for it Dan!

Judging by how fast the last 10 years has flown by, I don't have that much more time with them where they want to hang out and build/fix/play with stuff with Dad.

I just ordered a pair of NiMh batteries and a charger. We should have something to play with either this weekend or next. And something to fix shortly after that

Thanks all, for the education.

 

[Dan Dubeau]

One memory that shook loose just now was all the pack rebuilding we used to do. Whether or not we were doing it right remains to be seen, but my Dad used to get the old 9.6v Makita batteries from work when they tossed them. Usually only one dead cell would wreck the pack, so it kept us in good cheap batteries both for the drills, and my truck for a long time. I have no idea where they went, but I still haven't went through all the boxes from his move yet, so they might be in there. Same with the charger maybe. I'm not sure I want to teach my son that, as then all my stuff would get torn apart to be "rebuilt" the same as my Dads stuff was lol.

 

[PeterT]

I've harvested cells out of tool packs, but mostly to replace them with better cells & keep the otherwise drill going. Even that can be challenging because they sometimes use slightly different form factor cells. Or use welded tabs & accordion the assembly. Or the case has kind of tamperproof moldings that get violated in the process.

Destroying a pack module to get the batteries is easy, but sometimes the welded inter-tabs are tin foil looking thin gauge compared to good quality copper (solder) bars for current levels RC motors can draw. The thing is, if you discover a dead cell mid pack, its actually high odds the neighbors are not far behind. Not always but it usually works out that way. One exception is some commercial packs had what I'll loosely call protection circuitry. I'm not electrically savvy but I'm told some are just sensing over-current & shut the motor down. Others were actually a rudimentary form of balancing/diagnostic. Fresh, new high capacity NIMH ae actually pretty inexpensive but its a minefield of bogus capacities & C-ratings so buyer beware. Best practice is to initial charge at a very low trickle rate with a new pack with mixed cells.

Generally the name brand tool batteries were pretty decent quality... for their time. They have moved to lithium so some of the old packs look pretty dated by comparison. And also beware of tricky knockoffs in plug & play packs. Some are OK & some are duds.

ACCESSORIES BATTERIES | MAKITA

Makita USA: The Leader In Cordless with 18V LXT Lithium-Ion. The best in class for cordless power tool technology. A leader in power tool technology for the professional.

www.makitatools.com

 

[Dan Dubeau]

The battery packs we use to rebuild and harvest cells from were the NiCad 9.6v Makita stick ones from the 90's. I don't think I've ever played with a NiMh one, and certainly not a lithium one. I am pretty curious about the lithium packs though, and may dig into a Makita 18vlxt I have here that won't charge anymore.

I'm partly curious because A, I want to to about rebuilding them, and B, I have a few ideas for battery powered tools/accessories I want to make and want to know that whatever I hook up to the other end of them isn't going to fry the pack. I think all the protection circuit is built into the Makita packs, and not the tools, but I'm not %100 sure. I can 3d print the mating tool side for the battery packs, and from there incorporate them into whatever tool I want.

 

[PeterT]

LXT are lithium ion so you need to know what you are doing for a couple reasons. They will very likely have wiring to each cell which needs to be preserved & functional. The chargers require these discreet voltage levels in order to do their job correctly, applying appropriate voltages so the pack as a whole comes up in a controlled manner. Also, some lithium devices tie into this wiring to boards that protect them from over-discharge. If you over discharge lithium, they are pooched. Other lithium tools/devices use cells where the the smarts are on a tiny board within the cell itself. NI charging is kind of dumb charging, power goes in one end, through all the cells in series & out the other end. Hopefully the cells are somewhat similar voltage state & condition. This is why a bad cell in a pack an degrade the entire pack more rapidly.

If you are going to go lithium just get an RC (polymer) pack & matching decent charger. Your local fire department will thank you LOL.