6V battery substitute

A friend inherited a small dirt bike.  It has a quite deceased
6V battery. 

It's got a coil and points, not a magneto. So it needs a
battery, or substitute, to run.  (He's happy to kickstart.)  

It gets stored for long periods.

He asked if a super capacitor might work.  He can charge it
before starting. I'm debating in my head if it has a low enough
impedance to keep things stable.

Opinions?
-- 
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On 2020-05-27 20:50, David Lesher wrote:
> A friend inherited a small dirt bike.  It has a quite deceased
> 6V battery.
>
> It's got a coil and points, not a magneto. So it needs a
> battery, or substitute, to run.  (He's happy to kickstart.)
>
> It gets stored for long periods.
>
> He asked if a super capacitor might work.  He can charge it
> before starting. I'm debating in my head if it has a low enough
> impedance to keep things stable.
>
> Opinions?
>

I ran my old Citroen 2CV sans battery for a long time. It had a 6V 
system and a crank. I used a stack of three and sometimes four D-cells 
for starting, afterwards it continued on its generator. Worked fine for 
years. That stack of D-cells lasted more than a year.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Wednesday, May 27, 2020 at 11:50:08 PM UTC-4, David Lesher wrote:
> A friend inherited a small dirt bike.  It has a quite deceased
> 6V battery. 
> 
> It's got a coil and points, not a magneto. So it needs a
> battery, or substitute, to run.  (He's happy to kickstart.)  
> 
> It gets stored for long periods.
> 
> He asked if a super capacitor might work.  He can charge it
> before starting. I'm debating in my head if it has a low enough
> impedance to keep things stable.
> 
> Opinions?

I'm using a supercapacitor in a design for a power fail alarm.  The issue is the same as yours, add batteries and it becomes a maintenance issue.  A supercap will last like other electronics without attention.  

But you may need a regulation circuit to limit the current.  I don't think the problem you will have is too high impedance, but too low.  A battery changes voltage significantly as you charge or discharge it.  The supercap will have a very low impedance in comparison and will load down the generator if the voltage is not matched.  

This one simulates fine.  The Rs value would need to be changed and the diode is likely not required.  The FET is good for up to 9 amps I think and should be ok for 6 volts.  You may want to add some overvoltage protection though.  A hefty diode in the reverse direction to allow starting or maybe it isn't needed if the starter and alternator don't need to be connected directly.  

-- 

  Rick C.

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

On Thursday, May 28, 2020 at 1:37:17 AM UTC-4, Ricketty C wrote:
> On Wednesday, May 27, 2020 at 11:50:08 PM UTC-4, David Lesher wrote:
> > A friend inherited a small dirt bike.  It has a quite deceased
> > 6V battery. 
> > 
> > It's got a coil and points, not a magneto. So it needs a
> > battery, or substitute, to run.  (He's happy to kickstart.)  
> > 
> > It gets stored for long periods.
> > 
> > He asked if a super capacitor might work.  He can charge it
> > before starting. I'm debating in my head if it has a low enough
> > impedance to keep things stable.
> > 
> > Opinions?
> 
> I'm using a supercapacitor in a design for a power fail alarm.  The issue is the same as yours, add batteries and it becomes a maintenance issue.  A supercap will last like other electronics without attention.  
> 
> But you may need a regulation circuit to limit the current.  I don't think the problem you will have is too high impedance, but too low.  A battery changes voltage significantly as you charge or discharge it.  The supercap will have a very low impedance in comparison and will load down the generator if the voltage is not matched.  
> 
> This one simulates fine.  The Rs value would need to be changed and the diode is likely not required.  The FET is good for up to 9 amps I think and should be ok for 6 volts.  You may want to add some overvoltage protection though.  A hefty diode in the reverse direction to allow starting or maybe it isn't needed if the starter and alternator don't need to be connected directly.  

Forgot the link...

http://arius.com/temp/Current_Limit.pdf

-- 

  Rick C.

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

On 2020-05-28, David Lesher <wb8foz@panix.com> wrote:
> A friend inherited a small dirt bike.  It has a quite deceased
> 6V battery. 
>
> It's got a coil and points, not a magneto. So it needs a
> battery, or substitute, to run.  (He's happy to kickstart.)  
>
> It gets stored for long periods.
>
> He asked if a super capacitor might work.  He can charge it
> before starting. I'm debating in my head if it has a low enough
> impedance to keep things stable.
>
> Opinions?

PM or variable field generator?

-- 
  Jasen.