Maker Pro
Maker Pro

Lead Acid Battery Desulfator circuit help

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
You should be able to purchase access to a single Silicon Chip issue. Access to errata in their magazines is free, so if there are any updates you'll be able to read them too.

The main thing you'll get from it is the method of operation.

For 1kHz, the mosfet needs to be on for 50uS every 1ms. The inductors are 1mH and 220uH and the capacitor is 100uF.

Some rough "back of a napkin" calculations are that for 3000 times the frequency, you would require the mosfet to be on for 17ns each 330ns, appropriate inductors would be 330nH and 70nH, and the capacitor around 0.033uF

In the SC article, they use a IRF540N. This has a gate charge of 71nC. By my estimation, if you want to turn the device on and off in (say) 4ns (which for this circuit is probably too slow) then you need a gate current of around 18 amps. That is way too high (the specs suggest that you should expect a turn on time of 11ns and a rise time of 35ns, so lclearly this device is not appropriate) . A mosfet with higher Rds(on) will have lower gate capacitance.

Another random mosfet, ST 5NE10L-1 has a lower gate charge (around 10nC, but a higher Rds(on) of around 0.27 ohms). This *might* be able to be switched on and off fast enough. You would require a gate current of 4A probably.

So, So all you require is a driver capable of delivering a 4A gate current to turn it on and off. This is also a non-trivial exercise (the gate current probably approaches the current you're switching with the mosfet!

You probably need one of the other moderators to assist you with this.

Once you have figures all of that out, you need a way to prevent massive RFI as you will have created a very powerful RF transmitter. You will also need to minimise inductance in the leads to the battery or all that power will go precisely nowhere.

Many of the components (the mosfet and the diode at a minimum) will require heatsinking because there will be significant switching losses.
 

roltex_rohit123

Oct 12, 2009
92
Joined
Oct 12, 2009
Messages
92
You should be able to purchase access to a single Silicon Chip issue. Access to errata in their magazines is free, so if there are any updates you'll be able to read them too.

The main thing you'll get from it is the method of operation.

For 1kHz, the mosfet needs to be on for 50uS every 1ms. The inductors are 1mH and 220uH and the capacitor is 100uF.

Some rough "back of a napkin" calculations are that for 3000 times the frequency, you would require the mosfet to be on for 17ns each 330ns, appropriate inductors would be 330nH and 70nH, and the capacitor around 0.033uF

In the SC article, they use a IRF540N. This has a gate charge of 71nC. By my estimation, if you want to turn the device on and off in (say) 4ns (which for this circuit is probably too slow) then you need a gate current of around 18 amps. That is way too high (the specs suggest that you should expect a turn on time of 11ns and a rise time of 35ns, so lclearly this device is not appropriate) . A mosfet with higher Rds(on) will have lower gate capacitance.

Another random mosfet, ST 5NE10L-1 has a lower gate charge (around 10nC, but a higher Rds(on) of around 0.27 ohms). This *might* be able to be switched on and off fast enough. You would require a gate current of 4A probably.

So, So all you require is a driver capable of delivering a 4A gate current to turn it on and off. This is also a non-trivial exercise (the gate current probably approaches the current you're switching with the mosfet!

You probably need one of the other moderators to assist you with this.

Once you have figures all of that out, you need a way to prevent massive RFI as you will have created a very powerful RF transmitter. You will also need to minimise inductance in the leads to the battery or all that power will go precisely nowhere.

Many of the components (the mosfet and the diode at a minimum) will require heatsinking because there will be significant switching losses.

I have the circuit diagram of the circuit you suggest me from the issue. the inductors you suggest i'l definitely make them and use more wire and keep the diameter about an inch. so it wont get hot. i had a question regarding the mosfet. can't we make one from appropriate diodes and assemble it on the board. this way we would get rid of most of the heat. i could use heat paste on each of the FET component. this may be bigger but i think it could help. how can we minimise inductance in the battery leads?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
I'd be surprised if this will be workable. As I've suggested, turning the mosfet on and off fast enough is going to be very difficult.

You can't make a mosfet from diodes (if that's what you're suggesting).
 

roltex_rohit123

Oct 12, 2009
92
Joined
Oct 12, 2009
Messages
92
I'd be surprised if this will be workable. As I've suggested, turning the mosfet on and off fast enough is going to be very difficult.

You can't make a mosfet from diodes (if that's what you're suggesting).

i just wanted to know that since the mosfet is a small ic we could have its equivalent seperately constructed. it woud be as per our needs. if thats a stupid thought of mine please excuse me.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
A mosfet is a single component. Whilst it may be packaged similarly to other integrated circuits, it's not one.
 

poor mystic

Apr 8, 2011
1,074
Joined
Apr 8, 2011
Messages
1,074
Hi!
What a funny way to desulphate a battery!
I'll describe how I used to do the job long ago for BIG battery installations.

You need to charge at the 1/10th ampere hour rate, watching and recording electrolyte density in each cell, until it is as charged as it'd going to get according to the electrolyte density.
Then you need to discharge, at 1/10th of the ampere hour rating of the cells. That means using a suitable resistor. Once the worst cell has been fully discharged to its lowest not-stuffed-yet voltage start charging once more.
Through repeatedly charging and discharging the battery to the limit of its capacity the battery will progressively improve. Either that or it's too late.

I wouldn't leave this job to a circuit I made one day. Not if I wanted good results, anyway. The most important reading is after all electrolyte density which is usually measured using a float hygrometer. This is what tells you whether the sulphate is back in solution.

I spent quite a while doing this work while I was a technician in telephone exchanges. I remember much more than I've written down. Ask for help if you don't understand what I've said, and I'll try to clarify.
 
Last edited:
Top