Jerry-type pulser/desulfator using MOSFETs instead of transistors and going high-frequency

[The Crazy Noob]

Hi,

I've made a Jerry pulser (see circuit at the bottom of post) some time ago to revive dead car batteries and to use them for my first small windmill (not built yet). I know about the "big no-no" around car batteries, but hey, they are free where I get them :-).

Annyway, I managed to blow up that pulser (blew up some transistors) and I found that the costs of replacing the transistors was higher than the costs of buying power MOSFETs. I have never worked with MOSFETs before, and they seem to hate static charges and strange voltages at the gate. They do allow higher frequencys, and with all the talk going on about the inner resonance frequency of batteries, that might be a bonus.

About my (brief) experiences with the other pulser: I have so far tried to pulse 2 car batteries (one 100Ah, and another one 80Ah) and they both had one cell that just wouldn't gass. Does that mean that it's shorted? I had no obvious heating of the battery or that particular cell. I pulsed it about 30hrs or so, with an average current of about 2 amps (measured with an analog meter that was swinging between zero and the peak current, so I guess that it's about the average current) and a frequency of 200Hz or so with a capacitor of 900µF, pulse voltage was 30V.

Now, has annyone made a Jerry-type pulser with MOSFETs, or can annyone say what I must change to the original circuit (I have no experinece with MOSFETs)? I'm going to buy four N-channel MOSFETs, 200V, 30A and will be using 2 parallelled for both the cap charge and the cap discharge. I'm thinking of going to 1kHz (see the shaka link) or greater. Will those opto-couplers be able to hold up those frequencies? (didn't realy see the max frequency mentioned in the data sheet). Should I need that transistor to activate the two parallelled MOSFETs and keep the load off of the opto-couplers, or will that have to be a (less beefy) MOSFET too; or can I loose it all together?

And I was thinking, now that I would have the possibility of the high frequencies, the pulser might evolve into a MPPT circuit with PWM-control to the 555 timer if I have the time, and if I'm willing to learn micro-controller programming :-).

The original Jerry pulser/charger: (resized to be 100kB, original one here: http://www.otherpower.com/images/scimages/5232/jerry_charger.jpg)

[RogerAS]

Hi,

I really love that little 555 chip. I have driven small Fets directly from the output pin, but a better thing to do would be include a small transistor to up the signal to the gate. I don't really think you need optocouplers but that's just me. If you had a set of equal rating P channel FETs this would eliminate the need for the feedback between the directional DC pulses. That would make the system more responsive, but good P channel FETs seem hard to find for some reason, or not as readily available it seems. (Tiny P Chn FETs can be found in the base of CFL {Compact Floresecent Lighting}).

I feel all one needs to do to create a pulse that will "ring" a battery like a bell, is to provide a one way pulse. A square wave neg works. Just use the 555 output, pin 3, to drive a small transitor to up the drive to the gate(s). One can parrallel several FETs on a common heatsink and push serious amperage at some impressive voltage. If coupled to a big resonant coil some interesting effects can be created, or 6V DC could be pumped up to much higher pulses, similar to an old fashioned automotive ignition coil. Good capacitors and resistors on the timing side of the 555 is important for precise operation. Controlling input voltage down to 5V with a LM7805 and adding a shock absorber capacitor is a good idea, as voltage swings "seen" by the 555 can cause triggering issues...

I've made pulse chargers for drill battery packs and all sorts of other small rechargeables using a 555 and a few other parts. It's easy and it works. How fast? It all depends.

Sure a programable chip solution would, or could, be best. I won't argue that, but there are simple solutions to hours of programing and tweaking. I feel that coding with a perf board is still quicker than many other methods in some instances.

Below is a common design I modified using 2 555's. It works. In order to drive more FETs I would add a PNP(?) transitor to the output pin (#3) on 555#2. If the Supply is a big fast discharge source and good conductors are used one really stout FET could be driven by the 555 without an amplification transistor. The 555 will only flow so much current, and that so much is very little. A good FET should switch on with very low current requirement, but when you start adding more the issue becomes serious enough to consider the transistor solution. Anyway here's a hillbilly solution to pulse control as seen for 12V nominal systems.

Remember to heatsink all FETs and other heat generators, like the LM7805, the blocking diode on the positive lead, etc...Be safe and have fun!

[asheets]

So, what freq does this pulser work at?  Mine (based on http://www.otherpower.com/images/scimages/231/pulsecrg.GIF) works at 60Hz, and seems to do the job just fine.  Any advantages of different frequencies?

[The Crazy Noob]

RogerAS:
Wow, that circuit is sorth of giving me a head ache :-). Can you explain the workings a bit further? Are you dumping C2 into the battery? Or are you just switching the source to connect and charge the battery on and off quickly?

asheets:
Ah, the watergas-circuit. Well, it works for sending current through a battery with a high internal resistance, but, it doesn't use the internal resonance frequency (which needs: high and short current spikes like the ones from a capacitor). I believe that the cap charger/dumper would help decrease internal resitance more. However that circuit is a neat little (constant) current-source.

[for the people getting the error of the too large subject line when replying]: just reduce the subject to something shorter like I did here...

[DaveW]

  This is devilishly hard to read.  Coundn't you make the image small enough to

fit the page in the first place?  Scrolling back and forth to read the text

makes it very difficult to follow.

[RogerAS]

Dave,

Sorry if this messed up, but the file fits well within board specs. It's a simple file. On my Mac running Safari it looks fine, if not a triffle small.

Editors, if this posting looks funky 'cause of my graphic delete it ASAP!

[RogerAS]

Noob,

The caps marked C1 and C2 are to set the frquency and duration of pulse, and are of little to no concern in the charging aspect aside from their use to establish how often a pulse occurs and how long that pulse occurs respectively. Small values in uF ratings will yield proportionally shorter duty cycles in both positions. A 10uF 25V electrolitic aluminum will give about .1 second to 1 second multivibrator function, with ther resistance shown, for more precise control use higher quality caps such as tantilum(sp?). Rotary switches to bring in or cut out capacitance would make this a sweet little timer. I wonder if varibale caps would work?

This beast can be fed any DC source up to the LM7805's rating. This allows for fairly concise pulse timing and rather high htrz with tiny caps at C1 & C2. It's simple really. Yes it just connects the DC source to Drain in square waves. I used it with several small windturbines based on steppers to build up a good charge in a gang of caps(source) and then pop my batery bank (drain) every so often. I've also used it backfeeding the same battery bank.

Anyway, if the image messed up the thread I'm really sorry.

[The Crazy Noob]

You can't help it (so don't blame yourself :-) ), it's just how this board works: it sets all images to 80% of the total width of the screen which can give some strange results and apperantly, we aren't allowed to change the "width=80%"-tag in the html-code.

[TomW]

Roger;

Well, here on Firefox 2.0 and Mac OS X it looks fine. He must be using one of those non standard browsers that are supposedly a part of that [expletive deleted] OS?

Hard to make everything work for everyone.

Cheers.

TomW

[Gordy]

I know enough about computers to be constently getting in trouble with it. And if I tried to post somehting like that it would come out wrong too. This is not a new problem here.

Which leads me to ask why someone on the server end, with a lot more computer smarts than I have can't come up with a program to auto resize things to fit the screen. Like "outlook express" has for out going attachment to an email.

Just wondering,

Gordy

[alibro]

Maybe our host could put a wee heading on the front page something like

Best viewed on Firefox, or Safari, or Netscape or anything you like except In**t Ex**r.

I started reading this board on IE7 and had to switch to Firefox to see it properly.

AliBro

[ghurd]

Try 'right click', then 'view image'.

Thanks Commanda,

G-

[DaveW]

  RogerAS -

    No, not your image, it is a 620X439 and fits well.  The first one is a 1619X1259 image that on my machine takes multiple scrolls to see.

  TomW -

    Yes, I'm back to using the (expletive deleted) OS, linux and foxfire lock up on me.  I traced it back to a program that I must have on my machine (my CAD). I have used it for over 20 years and have too many libraries written and tested to change.  The best approach might be to set up another machine for the internet, but I'm trying to hold down on power usage.  At any rate, I did not mean to start a firestorm.  I simply thought we were asked to hold images to 640X480.  I withdraw my objection, I can live with skipping the wide bodied views.

[alibro]

I tried right clicking in IE7 but can't find any 'view image' option

AliBro

[RogerAS]

Dave,

No problem here with either the ?'s or anything else.

I just had to spend most of the day, today, recoding a shopping cart setup to allow for some of those IE issues. This site is set up with frames, and in Safari the cart works perfectly from inside those frames. Trying this in IE results in forcing me to make new windows to pop up or rebuilding the entire site just for IE users. Clicking the add to cart button from within IE and those frames returns a null input and adds nothing. Yet outside those frames the item is indeed added to the cart. <sigh>

Guess which happened?:-) I may redo the whole thing, someday, just so IE users can have their limited web experience and everyone else can get their groove on as well. <wink>

Anyway, I thought I had it (image) small enough as per board regs.

Sorry for being a graphics freak too. It really sucks to be going blind in a visual business!<grin>

[Gordy]

Same here, I get a veiw source, thats not it. Even tried scrowling up to the diagrams and right clicking on them. NO luck

Gordy

[RobC]

On my desulfator circuts I use one 555 set up with the diodes on the timing side to give me adjustable duty cycle of 0 to 100 percent. In order to change frequency I just change the timing cap. To protect the 555 from spikes I use a large filter cap and a 15v 5 watt zener across  across the power supply to the chip. Not having enough voltage drive for the mosfets doesn't seem to be a problem. As far as opto isolators I wouldn't waste my time. In all my circuits  I use an IC sockets that way if I fry a 555 I just pop it out and put in a new one which happens seldom if ever. Back to the drive current issue in my dump load I run 5 irf 540's with a 555 output and in my 8 ft fluorescent light drivers I drive a single irf 640 at 18 Khz at 5 amps. I do have a simple transistor drive boost circuit if I feel I need it. So far I haven't. As far as transistors vs mosfets, give me the mosfets anyday they are tough and the price is right. I also really like large power Igbt's if you can find them second hand. As far as being an expert on desulfating I'm not, I am still in the learning and experimenting      

stage and the important thing is it's a lot of fun! If this helps great if not just ignore it. For what its worth RobC

[jimjjnn]

I empathize with you Roger as I am blind in one eye and have a little blind Pug dog that is totally blind but happy.

[The Crazy Noob]

Ok, I've made a quick drawing of a circuit, but I'm still confused about how to put the MOSFETs in the circuit. I do think that I will need to use optocouplers or transistors to get the waveform to the supply voltage (30V) because I don't like the 555 working at those voltages. Also, would I need an N-channel and a P-channel MOSFET to trigger them on the top/bottom part of the waveform? Or can I do that with the same type (N-channel) of MOSFET, but position them differently in the circuit?

Annyway: here is the circuit, don't shoot the pianist if it's wrong :-)

[asheets]

But, what range is the "internal resonance frequency"?  And, can you provide a reference or a definition of what it is?

[Nando]

I am going to try again, to respond to you, regarding this circuit.

The use of a HUGE capacitor to generate a power pulse is highly un-practical.

Reason ONE : The frequency is low and the rise time due to the ESR ( effective Series Resistance of the capacitor plus the Equivalent resistance of the Darlington going ON to discharge the capacitor is high.

Most to the energy is dissipated by the huge capacitor and the Darlington transistor, this transistor may be getting quite warm since it takes around 80 to 85 % of the energy that YOU pretend to transfer to the battery.

The energy transfer is the ratio of the battery internal resistance and the sum of the Mosfet plus the ESR of the Capacitor, which is going to be close to to 12 times higher than the battery ESR.

The discharge time may be close to 140,000 micro-farads * around 1 OHM = 0.14 seconds, the peak current pulse may run around 30 amps.

BEST SOLUTIONS to this problem is the arrangement of pulsing the battery with a fast current pulse.

Drop the Capacitor, it is totally un-necessary and it is just a load to you.

You will accomplish the same if, You drop the lower semiconductor, the capacitor and leave the upper Darlington or You replace it with a MosFet, with one ( 1) Ohm series resistance.

The one ohm, is to protect the MosFet.

If you are interested in a practical circuit along these lines, let me know.

Nando

[elvin1949]

 It ain't just here.

Internet Exploder don't work anywhere.

later

elvin

[The Crazy Noob]

How would the inductive type (+ trickle charger) compare to the type you are proposing?

[Nando]

The pulser like I am proposing here is quite equivalent to the one using a choke to store energy then dumping it into the battery.

And the desulfating will be around 4 times better than the available kits or presently available low current devices.

What is important is the initial rise time to allow the pulse to penetrate the electrolyte deeply, before the electrolyte reacts to the pulse.

Many people talk about frequency resonance, and since I do not want to start an endless discussion, I will not enter in this Boxing Ring.

10 to 20 microseconds is more than sufficient for such pulser, a one ohm diode limits the current to about 20 amps and repeated every one millisecond the power "pushed" into the battery would be .

The current "ingested" by the battery is 20 * (20E10^6)* 1000 = 400 milliamps

The dissipation of the MosFet is going to be : 400E10^-3 * Rdson = around 80 to 400 milliwatts -- since I do not know what type of MosFet is going to be used.

The design is specific to the availability of a higher supply voltage.

For other systems that have equal or lower voltage than the battery in desulfation process, the pulser has to be done differently.

Again, the initial rise time is the "major" factor that the sulfated battery needs to see to start allowing desulfation.

Nando

[The Crazy Noob]

Hmmm, so you could see it as just a PWM-circuit? Short pulses from a regular (high current) power supply?

I might go for PICAXE to do that with the power from a wind turbine and get some sorth of MPPT routine in there. This would essentialy be the same thing, correct?

[Nando]

I am not familiar with the Picaxe, at all.

MPPT if you are charging a battery, but for this case is for desulfating the battery, two different jobs.

Am I responding to a wrong thread ?.

MPPT is done in a complete different way, for one constant current charging that is variable depending on the variable power being fed to the charger, so the controller needs to define the power entering into the "pipe" to regulate or vary the charging current to keep the incoming voltage and power at the MPPT peak point.

Nando

[The Crazy Noob]

Never mind, the MPPT-part was a little spin-off in my brain to use the system 24/7, powered from a wind turbine, and to keep the batteries up :-).

Annyway, I'm starting to think that a direct grid-tied inverter is probably the best - no battery inefficienties, no battery replacement, not having to worry about the batteries being full, ... .

[Nando]

Crazy Noob:

A GRID tied system without batteries, call from the beginning for a high voltage generator with proper design parameters.

PEAK POWER First

Peak Voltage second]

Conversion from the lowest generator voltage to the REGULATED DC voltage for the GRID tied inverter ( some for 120 Vac, a link of 400 DC volts, and for 220 AC volts, 600 DC link).

MPPT full range.

This implies the equivalent of a PFC converter to bring the voltage up to 400 volts or 600 volts -- some may have conversion from higher voltage (like 600 to 1000 volts down to 400 and/or 600 Vdc for the link).

Some may do the mistake of using a CLIPPER to limit the upper voltage -- to be able to present a lower cost MPPT inverter or charger

ELC at peak power if the inverter has limited peak power. (This is a CLIPPER).

GRID tied Inverter takes time to make it in production and needs some kind of certification -- so costly to design and produced it.

Nando

[Nando]

I finally got what you really meant.

Yes you could add a desulfating pulse so often when You are charging, I used to do that with some Very special batteries -- remember the rise time is the important point.

Nando