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cheap way to charge nimh with dt/dt

Anyone have a good way to charge a 10 cell, 12V nimh pack as follows:

- 0.35A to 1.5A charge current (not adjustable, but in that range)
- dt/dt charge termination and overtemp termination
- input voltage 12V

For less than 2$ at 5000 qty say?

AC
 
L

linnix

Jan 1, 1970
0
Vin = 12VDC???

A boost smps, controller and temp sensor for less than $2.00US@5000
All I can say is...'Those poor workers in asia'. :(

Indeed, only $10,000 for ASIC alone. So, $25,000 for 25000 is doable.
 
M

MooseFET

Jan 1, 1970
0
Vin = 12VDC???

A boost smps, controller and temp sensor for less than $2.00US@5000
All I can say is...'Those poor workers in asia'. :(

Nobody said anything about efficiency or the range of that 12V input.
I'm thinking of a boost circuit that just uses a free running
oscillator of some kind.

The inductor is likely to be the most expensive part in the circuit.
The housing and the bare PCB are likely to add up to more than the $2
limit.
 
N

Nico Coesel

Jan 1, 1970
0
Anyone have a good way to charge a 10 cell, 12V nimh pack as follows:

- 0.35A to 1.5A charge current (not adjustable, but in that range)
- dt/dt charge termination and overtemp termination
- input voltage 12V

For less than 2$ at 5000 qty say?

A cheap uC with internal temp sensor, an inductor, a MOSFET and a
diode may do the trick. Pulsed trickle charge comes for free.
 
M

MooseFET

Jan 1, 1970
0
A cheap uC with internal temp sensor, an inductor, a MOSFET and a
diode may do the trick. Pulsed trickle charge comes for free.


You could make it short circuit protected if you did this:

----- To ADC
!
+-----[Battery]-----
! !
! !
-+--))))))---+--->!--
!
!
!!-+----To ADC
--!!
!!-
!
GND


The micro pulses the MOSFET and trips the ADC just after it switches
the MOSFET off. Applying several cooks constants to the ADC
measurements, you get the battery voltage.

Pulsing the ADC several times there after would let the micro watch
for the inductor current stopping before it turns the MOSFET on
again.

 
E

Eeyore

Jan 1, 1970
0
Anyone have a good way to charge a 10 cell, 12V nimh pack as follows:

- 0.35A to 1.5A charge current (not adjustable, but in that range)
- dt/dt charge termination and overtemp termination

dV/dt surely ? Or did you mean dI/dt ?

Graham
 
S

Spehro Pefhany

Jan 1, 1970
0
dV/dt surely ? Or did you mean dI/dt ?

Graham

He means dT/dt (rate of change of temperature). Around +1K/minute is
an indicator that the cell is pretty much fully charged and is now
converting most of the incoming charge energy into heat. The dv/dt
depression termination does not work in many circumstances.


Best regards,
Spehro Pefhany
 
E

Eeyore

Jan 1, 1970
0
Spehro said:
He means dT/dt (rate of change of temperature). Around +1K/minute is
an indicator that the cell is pretty much fully charged and is now
converting most of the incoming charge energy into heat.

Understood now. Philips (NXP) do some ready to go chips for that as do a few
others. Blowed if I can think of names no but certainly one slightly specialist
US semi co. Wouldn't be surprised if On-Semi have something in their range
either.

The dv/dt depression termination does not work in many circumstances.

Really ? That's a bit of a nuisance ! I wonder how many chargers were built
using that method !

Graham
 
J

Jasen Betts

Jan 1, 1970
0
Really ? That's a bit of a nuisance ! I wonder how many chargers were built
using that method !

One of those is the OP's case. If the 10 (assumed series connected) cells have
slightly different charge levels they'll all hit the dV/dt hump at different
times and the voltage at the end terminals won't show a clear 'full' signature.
 
E

Eeyore

Jan 1, 1970
0
Jasen said:
One of those is the OP's case. If the 10 (assumed series connected) cells have
slightly different charge levels they'll all hit the dV/dt hump at different
times and the voltage at the end terminals won't show a clear 'full' signature.

Good point.

Graham
 
K

krw

Jan 1, 1970
0
One of those is the OP's case. If the 10 (assumed series connected) cells have
slightly different charge levels they'll all hit the dV/dt hump at different
times and the voltage at the end terminals won't show a clear 'full' signature.

If they're so poorly matched that they don't hit the hump at close
to the same time, one or more will likely get reverse charged at
the other end of the curve. Either way, batteries with poorly
matched or weak cells will be toast.
 
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