Battery replacement

On Fri, 13 Aug 2021 09:21:54 -0700, Ralph <Ralph@Ralph.com> wrote:

>I have a remote control car
>It uses a 8.4v nicad battery that I cannot find and really want to NOT use.

>I want to replace with Li Ion cell type.

Consider LiPo in stead. They are less expensive, higher specific
energy, and can output tremendous current. They are used in pretty
much all hobby remote control applications these days. You can have
them in a huge variety of sizes and shapes, so you should be able to
find one that will fit.

>I need help designing the replacement.

The problem in your case, is that the voltage you need cannot be
achieved with any Li based battery. A two-cell battery would have a
nominal voltage of 7.4 V, while a three-cell would have 11.1 V. You
would have to choose between poor performance or spectacular
performance with the risk of cooking the motor.

Personally, I'd get the three-cell, and when something burns out,
replace it with something better. But for a Christmas toy, that may
not be worth the money.
-- 
RoRo

On Friday, August 13, 2021 at 2:35:00 PM UTC-4, Fred Bloggs wrote:
> On Friday, August 13, 2021 at 12:21:57 PM UTC-4, Ralph wrote: 
> > I have a remote control car that has a dedicated control and receiver at 
> > some unknown to me frequency. 
> > Not bluetooth or wifi. 
> > It was a Christmas toy. 
> > It is a substantial car nearly 18" long. 
> > It uses a 8.4v nicad battery that I cannot find and really want to NOT use. 
> > I can get the battery specs if needed. 
> > The car is on vacation in the mountains right now. lol 
> > 
> > I want to replace with Li Ion cell type. 
> > 
> > I need help designing the replacement. 
> > 
> > Suggestions or instruction please.
> Look into NiMH, nickel metal hydride, a direct replacement for NiCad. You should be able to find the exact same form factor and capacity. May need a new charger though. Stay clear of lithium, no justification for it.

NiMH has a higher internal resistance than NiCad and may not work as well in a high current drain application like a car.  That's why they still use NiCad in many tools rather than NiMH.  Of course, many are now lithium ion.  So clearly not a bad choice. 

-- 

Rick C.

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Rick C <gnuarm.deletethisbit@gmail.com> wrote in
news:30305977-11b1-4c7e-bb50-83192d62dba8n@googlegroups.com: 

> NiMH has a higher internal resistance than NiCad and may not work
> as well in a high current drain application like a car.  That's
> why they still use NiCad in many tools rather than NiMH.  Of
> course, many are now lithium ion.  So clearly not a bad choice. 
> 

NiCad sucks and has been phased out for half a decade.

  Nearly every small application these days is Lithium ion.

Switched out my 6Ah SLA motorcycle battery for an 8Ah LiFePo battery 
that was the same form factor all but just 1/4 inch taller.  It 
operates better than the other.  It should...  it was two to three 
times the price.