simple desulfator circuit - question

[lynx]

hi, i did the following desulfator circuit, but the 1mH indutor gets burned all the time,

http://members.shaw.ca/pferlow/schematic.gif

i'm using one 220uH rated for 6A and one 1mH rated around 100mA, i can't
see any mistake on my circuit.

thank you of any help..

 

[MrAl]

Hi,

If everything else is working right then the 1mH inductor has to be rated for a higher current.

 

[NorthGuy]

When the FET is on, the current through the inductor increases at a rate of 12000A/s. It only takes 8us for it to go to 100mA. Much longer than this, and it'll be lot more than 100mA.

 

[lynx]

hi, i thought i could temporaly replace the 1mH inductor with a wire so i can take some measurements
but the mosfet got fried...i don't know where to look for a mistake, everything seems ok by looking at it.

 

[NorthGuy]

hi, i thought i could temporaly replace the 1mH inductor with a wire so i can take some measurements
but the mosfet got fried...

Of course. The inductors are there to limit the speed at which the current can rise. You need to make sure that the FET switches off fast enough, so that the current doesn't rise too high.

 

[lynx]

might be a 555 problem? i mean it doesn't give a pulse maybe?

 

[dr pepper]

I get the 555 running at 1.2kc, a 1000uH choke as mentioned at that freq will be pulling about 5 amps (assuming all the energy is absorbed during the off cycle), averaged out would be approx 1.25 amps.
Both the inductors must be rated for more than 5 amps, if not they will saturate and act like pieces of wire shorting the supply and frying the fet, the 1000uH is the one more likely to be lacking current wise.
You could wind a pair of chokes using enameled copper wire, there are several audio sites that will calculate what you want as these are popular in speaker crossovers.

I looked into a similar circuit, might be the same one a while back, as I have a boat that uses domestic batteries and I wondered if they could be revived, however there is some conjecture about this technique as to whether it works or not so I didnt bother.

P.S. if the circuit becomes disconnected from the battery theres a chance the fet (the choke will protect it a little) will be zapped (or the operator for that matter) by back emf, its good practice here to stop the 555 before pulling the power.

 

[lynx]

I get the 555 running at 1.2kc, a 1000uH choke as mentioned at that freq will be pulling about 5 amps (assuming all the energy is absorbed during the off cycle), averaged out would be approx 1.25 amps.
Both the inductors must be rated for more than 5 amps, if not they will saturate and act like pieces of wire shorting the supply and frying the fet, the 1000uH is the one more likely to be lacking current wise.

i didn't knew that.. :O also the informations i got say the 1mH inductor should be around 100mA, by the way check
this ready made from ebay...how come it uses so small inductors? both are small...

**broken link removed**

also what you have just said that the 555 should power down first...looks like serious issue......

 

[4pyros]

I looked into a similar circuit, might be the same one a while back, as I have a boat that uses domestic batteries and I wondered if they could be revived, however there is some conjecture about this technique as to whether it works or not so I didnt bother.

I have been using a commercial desulfator for some old SLA batteries from exit signs and the batteries have lasted for years.

 

[dr pepper]

Ok, hmm maybe I was wrong somewhere there then, if they are available and dont blow up maybe they do work.
The circuit must rely on little difference voltage wise bewteen the battery and the voltage at the chokes.

Mr. pyro were you using the desulphator on a new battery or reviving an old one?

 

[4pyros]

Ok, hmm maybe I was wrong somewhere there then, if they are available and dont blow up maybe they do work.
The circuit must rely on little difference voltage wise between the battery and the voltage at the chokes.

Mr. pyro were you using the desulphator on a new battery or reviving an old one?

As stated the batteries came out of exit signs. I revived them and used them in my sons supped up hot wheels car (Heavy Use) for about 5 years till he could no longer fit in the car. Then he used them a few more years in an electric scooter. I still have and use them today.
I made 7 packs with two 6 volt batteries each.
I use two of theses for my SLAs;
**broken link removed**

 

[dr pepper]

You did well then, in such an application they'd usually only last a year or 2.

 

[4pyros]

The stock batteries are made to die. Cheep batteries, a poor charger that over charges them and cooks them, and no advice on how to properly care for them. The average consumer could kill the batteries in a power wheels in less then a year.

 

[dr pepper]

On a boat even with an intelligent charger leisure batteries still dont last more than 2 seasons, 3 for an ingersoll that costs 3 times an ordinary battery, the weather and disuse during winter might have something to do with that though.

 

[lynx]

what about the problem with the circuit can you help me out?

 

[4pyros]

What value cap are you using for C2?
The schematic says .022 and the note says .0022.

 

[lynx]

What value cap are you using for C2?
The schematic says .022 and the note says .0022.

im using 2.2nF, i care to know what could cause the 1mH unductor to constantly get burned..so i can figure iut what i might did wrong, thank you

 

[chemelec]

i care to know what could cause the 1mH unductor to constantly get burned..so i can figure iut what i might did wrong, thank you

Well considering this is FUSED for 2 AMPS, and Most of the Current goes through Both Coils. I Think it is Quite Obvious your coil is Too Low in a Current Rating.

 

[lynx]

Well considering this is FUSED for 2 AMPS, and Most of the Current goes through Both Coils. I Think it is Quite Obvious your coil is Too Low in a Current Rating.

there's no fuse in my built, let me upload some photos...

 

[chemelec]

there's no fuse in my built, let me upload some photos...View attachment 84722 View attachment 84723

OK, BUT THERE IS ON THE "ORIGIONAL SCHEMATIC".
SO, EXPECTED CURRENT DRAW IS PROBABLY BETWEEN 1 to 2 Amps.