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.

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.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209 

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 a sunny day (Fri, 13 Aug 2021 11:47:50 -0700 (PDT)) it happened Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote in
<245c28e4-8010-4aaf-9754-fe4028338bebn@googlegroups.com>:

>On Friday, August 13, 2021 at 2:43:40 PM UTC-4, Ed Lee wrote:
>> On Friday, August 13, 2021 at 11:35:00 AM UTC-7, 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.
>> Why? Lithium batteries are cheaper and higher capacity.
>
>Voltage is not compatible with his system, unlikely to find compatible form factor, (this thing moves so not a lot of leeway
>there), they're pricey, requires more expensive charger, and they're hazmat to the max.
>NiMH should be a drop -in. They used to have excessive self-discharge but that problem has been fixed.

8.4 / 1.2 = 7 eneloop AA
No self discharge, safe, does not catch fire,
charging is simple at 1.6V constant current.

Else I would go lipo, there are chargers for that,
lipo performed better in my drone than the li-ion stuff.
You only see lipos in drones.
Some lipo batteries have build in protection.
4.2V top, about 3.8 nominal, with 3 just more speed for the car..?
Very high current capacity,
If the car does not want more voltage you may need some switcher / regulator, that reduces efficiency.
Need more data.


  

> The troll doesn't even know how to format a USENET post...

As ironically stated by the John Doe <always.look@message.header> troll
in message-id <sdhn7c$pkp$4@dont-email.me> who has posted yet another
incorectly formatted USENET posting on Fri, 13 Aug 2021 19:12:52 -0000
(UTC) in message-id <sf6g7k$7b1$1@dont-email.me>.

Nonsense...

-- 
Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:

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> Date: Fri, 13 Aug 2021 11:47:50 -0700 (PDT)
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> Subject: Re: Battery replacement
> From: Fred Bloggs <bloggs.fredbloggs.fred@gmail.com>
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> Content-Type: text/plain; charset="UTF-8"
> Lines: 21
> Xref: reader02.eternal-september.org sci.electronics.design:640275
> 
> On Friday, August 13, 2021 at 2:43:40 PM UTC-4, Ed Lee wrote:
>> On Friday, August 13, 2021 at 11:35:00 AM UTC-7, 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.
>> Why? Lithium batteries are cheaper and higher capacity.
> 
> Voltage is not compatible with his system, unlikely to find compatible form factor, (this thing moves so not a lot of leeway there), they're pricey, requires more expensive charger, and they're hazmat to the max.
> NiMH should be a drop -in. They used to have excessive self-discharge but that problem has been fixed.
> 

On Friday, August 13, 2021 at 11:47:57 AM UTC-7, Fred Bloggs wrote:
> On Friday, August 13, 2021 at 2:43:40 PM UTC-4, Ed Lee wrote: 
> > On Friday, August 13, 2021 at 11:35:00 AM UTC-7, 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. 
> > Why? Lithium batteries are cheaper and higher capacity.
> Voltage is not compatible with his system,

It might not be optimal, but you can limit lithium batteries to upper or lower usage range and it can still be higher cap than NiCad or NiMH.
  
>  unlikely to find compatible form factor, (this thing moves so not a lot of leeway there), they're pricey, requires more expensive charger

DC module is around $3 and the 3582 charger chip is around 25 cents.  But the charge current is low with unmodified circuit.  With zener and by-pass mosfet, i can build one for around $5.

> , and they're hazmat to the max. 

True for Tesla, but the OP is not building millions.  

> NiMH should be a drop -in. They used to have excessive self-discharge but that problem has been fixed.

On Friday, August 13, 2021 at 2:43:40 PM UTC-4, Ed Lee wrote:
> On Friday, August 13, 2021 at 11:35:00 AM UTC-7, 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.
> Why? Lithium batteries are cheaper and higher capacity.

Voltage is not compatible with his system, unlikely to find compatible form factor, (this thing moves so not a lot of leeway there), they're pricey, requires more expensive charger, and they're hazmat to the max.
NiMH should be a drop -in. They used to have excessive self-discharge but that problem has been fixed.

On Friday, August 13, 2021 at 11:35:00 AM UTC-7, 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.

Why? Lithium batteries are cheaper and higher capacity.

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.