Battery replacement

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.

On Friday, August 13, 2021 at 9:21:57 AM UTC-7, 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. 

Need operating voltage range and max current. 2 serial (too low) or 3 serial (too high), N parallel.

> The car is on vacation in the mountains right now. lol 

Recall it. Cancel vacation.

> I want to replace with Li Ion cell type. 
> 
> I need help designing the replacement. 
> 
> Suggestions or instruction please.

On Friday, August 13, 2021 at 9:32:46 AM UTC-7, Ed Lee wrote:
> On Friday, August 13, 2021 at 9:21:57 AM UTC-7, 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.
> Need operating voltage range and max current. 2 serial (too low) or 3 serial (too high), N parallel.

And do you need fast charging?  I am current working on a 4.2V fast charger.  The DC supply can pump out 2A, but the charge controller can only handle 300mA.  So, i am thinking about by-passing it with a mosfet below 3.7V and pump max. current into it.  That's for each cell by itself.  I have one charger per cell.

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.

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 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.

Nonsense...

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

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> Subject: Re: Battery replacement
> From: Fred Bloggs <bloggs.fredbloggs.fred@gmail.com>
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> 
> 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.
> 

> 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>.

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.