New PWM Board from Bob?

[mos68x]

I saw mention of a newer version, so I thought I'd ask. Besides I may be interested if the limited current is high enough. If there isn't a new one and we're still on the E revision, then how high can it go on the current before it gets a wee bit too warm? Perhaps I was a bit hasty in selling all my boards to Kevin, but oh well. Now I find myself in need of a PWM for a DC-DC converter. Yeah I could buy one, but I want to find one that will handle several amps, at least 15A-20A. The rest of the circuit I can build myself, but I wanted to know what the limited current was on Bob's before I bought one online. If I can get this right, then I'll have both the trucks cell up and operational as well as the new bike cell.

Thanks
Leon

[kevinsatterfield]

Leon, rev.f is the same as rev.e Mr.Boyce moved a few diodes around that was a little tite...I still have a rev.c board if you need one for a PWM....for a small price....heh heh the rev.c boards used a bigger FET for yer higher current needs. The rev.e boards have a 36 amp Fet for each channel.The rev.c.boards have a 170 amp FET.You wuld have to look thru his files and fix the rev.c board cuz it had a mishap on it.

[spencyg]

I have 3 rev F boards on the way, and I don't intend to use them all....I may part with one if the offer is decent:) I would imagine a little research would come up with upgraded MOSFET's that could handle your desired current load. I have an 18A MOSFET on the bench which I think I picked up for like $12.00 or something....


Spence

[mos68x]

So we can interchange the MOSFET's without a problem then right? But if the PWM can handle a 30A load then I'm not going to be that worried about it, I'm just using it to drive the primary side of a coil for a DC-DC converter. With the max load that I expect on the secondary I don't see the load on the primaries being over 30A. Of course with a few rated capacitors I can smooth out the pulse and then power the cells.

[kevinsatterfield]

you might not wanna run 30 amps thru those fets but i may have a heat sink...soon as get this old TV apart I'll let ya know if you dont have a good heat sink....look at Bobs in his folder..you will definatley need one close that size.You will have to look at the turn on voltages and all that for any new Fet you wanna try.

[kevinsatterfield]

forgot ..the biggest problem you'd have put'n bigger FET on rev.e is leg space'n...rev.c has wider legs for bigger FETs.

[mos68x]

Wasn't there an issue with the Rev C build though? I can't remember what it was but I thought it had something to do with the freq stuff.

The only other thing I had thought about was to run two different PWMs on dual primaries. Only thing is I'm not sure if I can reduce it to a single secondary or not though, or if the two primaries would even do me any good.

[kevinsatterfield]

The rev.c boards out puts are combined from the board to a single out put and the rev.e boards are seperated.Bob may be able to tell you how to sperate the channels on a rev.c board to use those bigger FETs but if yer want'n to seperate frequencies to train into someth'n you gotta use a transformer.when you pulse a frequency thru a transformer the secondary piks it up thru induction I believe...so if you pulse one frequency the secondary piks it up and throws it out and if you pulse a diffrent frequency the same secondary willpik it up and throw it out to behind the first pulse.Im perty sure they have to be outta phase just a hair or they wuld be distorted if yer look'n for a certain frequency from the secondary.I think the way that works is when you wind the primarries .....I think it takes a certain amount of time in one dirrection or another for the secondary to pik up the signals and when you wind the primarries they gotta be spaced apart a certain phase relationship ..I think thats how you get the signals to pik up how ever ya want em to come out ...somethj'n like that....But you do use a seperate primary for each frequency to get em outta phase...sound right??.....the thing about the transformer tho is its gotta be able to pik those pulses up and throw em out nice and clear....laminated cores wont do that at high frequencies.But yeah the rev.c boards wuldnt work if you need a clean pulse or watever...you prolly wuld be better off use a chip made just for wat you want....ive got a link here somewhere for DC-DC converters that handle 20 amps with out a heatsink if you want me to find it I will....

[mos68x]

So what yer saying is that I'm better off building the Rev C board for what I want, lol. I don't need to output two different freq's and the only reason that I brought up multiple outputs was for extra power. So I would be better off using the single output of the Rev C board and putting it to the primary of whatever coil I finally get. Thanks for the input Kevin

[mos68x]

Hey, what is the lowest frequency attainable with the Rev C board?

[mos68x]

Guess I should ask what the upper and lower limits for frequency adjustment is instead, lol.
Have I mentioned how retarded it is not having an edit button?

[kevinsatterfield]

[mos68x]

[kevinsatterfield]

[Bob Boyce]

Leon, the rev C will work great for driving a toriod, just use one generator stage instead of all 3. Less parts count too since most of the parts won't be needed. A single FET in that board will handle 170 amps continuous rating and up to 670 amps peak in pulse mode. I still have some rev C boards left as well.

Bob