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where is the best place to a 70-80amp PWM
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timmtbird Offline
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Post: #1
where is the best place to a 70-80amp PWM
I have my dry cell plats coming soon and ill start building the cell right a way. but i need to know where to get a good PWM?

if someone could help me that would be great!
(This post was last modified: 12-15-2008 07:34 AM by timmtbird.)
12-15-2008 07:33 AM
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stl_hemi Offline
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Post: #2
RE: where is the best place to a 70-80amp PWM
ZFF has up to 75amps. I think their is a guy on ebay makings zff copies that says he can do up to 100amps.

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12-15-2008 07:45 AM
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colchiro Offline
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Post: #3
RE: where is the best place to a 70-80amp PWM
ZFF sells some too, but last I saw I think were over $200.

Rick

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12-15-2008 09:45 AM
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timmtbird Offline
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Big Grin RE: where is the best place to a 70-80amp PWM
alpha-dog Wrote:
timmtbird Wrote:I have my dry cell plats coming soon and ill start building the cell right a way. but i need to know where to get a good PWM?

if someone could help me that would be great!

You could use two 30 amp pwm's or even three slaved together.
Bakatronics is where I got mine and they are recomended to me.
They only cost about $35.00 each. they also have a 50 amp unit.
Russ

Hey that’s a great idea! 12g wire right? how would all that wire up? I think understand I would wire one pwm to the next and the to gen. thank a lot manSmile
12-15-2008 01:37 PM
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benny Offline
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RE: where is the best place to a 70-80amp PWM
timmtbird Wrote:
alpha-dog Wrote:
timmtbird Wrote:I have my dry cell plats coming soon and ill start building the cell right a way. but i need to know where to get a good PWM?

if someone could help me that would be great!

You could use two 30 amp pwm's or even three slaved together.
Bakatronics is where I got mine and they are recomended to me.
They only cost about $35.00 each. they also have a 50 amp unit.
Russ

Hey that’s a great idea! 12g wire right? how would all that wire up? I think understand I would wire one pwm to the next and the to gen. thank a lot manSmile

Easiest way is just to set up a number of power fets in parallel. No need for load balancing ballast resistor as in NPN/PNP type unijunction transistors. Make sure all the fets are of the same type.
Ultrafets are probably best due to very low RDS-on resistance.
You might need to vary the resistor value slightly between gate and source pins of the power fets to get best results.
Existing drive circuit, feeding gate will probably be ok as is.

Look at something like ultrafet HUF75337P3, rated for 55V, 62A.
RDS-on 0.014 ohms
Allow for some latitude in actual current draw and watch out for possible heating effect when running at high frequency of PWM. The current loading, as with all fets, needs to be downgraded depending on frequency and current. There are graphs for characteristics of these in the datasheet for same.3 of this type in parallel should be more than plenty for your needs

If you are handy with electronics construction, use the circuit which uses 555 timers for generating PWM pulse train.
If not, buy a cheap PWM and replace the power fets with a set of the above fitted to a heatsink. Cooling fan is optional, but preferable. I currently use two of these FETS in parallel at 20A plus, in my home brew PWM, and both run absolutely stone cold.

I wouldn't recommend slaving two PWMs for a single generator unless the generator can be set up to have different sections working independently. otherwise you may get conflicting outputs from multiple PWMs with power outputs tied together, manifesting itself in the form of unbalanced loading of the individual PWMs. This may lead to overloading of individual fets, leading to catastrophic failure of same. ie the smoke escapes from inside these fets. They won't function correctly if you let the smoke out.
(This post was last modified: 12-15-2008 02:26 PM by benny.)
12-15-2008 02:14 PM
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benny Offline
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RE: where is the best place to a 70-80amp PWM
alpha-dog Wrote:I have not set-up my pwm's yet myself but I did talk to someone who has. Two 30 amp bakatronic pwm's worked nicely for him. The ground (-) gets chopped and the 12vdc (+) is parallel. You can let them free run if you have something like my cell +NNNN-NNNN+NNNN-NNNN+. The pwm's only controll the (-).
Russ

For clarification. As I said, different sections need to be working independently.
Depending on type of PWM.
Most commonly used, Negative switching. the positive input of the PWM is usually connected to the negative terminal of the generator with the negative PWM connection going to ground. the 12V connections to the generator would be commoned to 12V, the positive connections for the PWMs would not. These would be connected as described. The negative connections of the PWMs would be commoned to ground.

In any case, which is the least expensive option? Two PWM units at $200 each, or one PWM (el cheapo) plus two or three power fets at around $3 each and, possibly, a small heatsink at a further couple of dollars?

Using two PWMs, there is the added problems/inconvenience of having to vary two PWMs to vary load/output, especially when trying to balance loading of same, when driving. Doable, but awkward.
(This post was last modified: 12-16-2008 02:45 AM by benny.)
12-16-2008 02:27 AM
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timmtbird Offline
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Post: #7
RE: where is the best place to a 70-80amp PWM
theres a guy on eBay that’s selling a PWM 60amp, EFLE MAP, Flash back arrestor, and FUEL HEATER for $65.00
http://cgi.ebay.com/ebaymotors/ws/eBayIS...%26otn%3D4
12-16-2008 04:51 PM
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Bassman Offline
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Post: #8
RE: where is the best place to a 70-80amp PWM
If the PWM's have a frequency adjust, I would make sure that the cells were seperated because the frequency of each PWM would have to be exactly the same or you would never get the current to balance between them.
12-16-2008 08:51 PM
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JET USA Offline
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Post: #9
RE: where is the best place to a 70-80amp PWM
Try E-Bay (search for pwm 30 amp)
Hi I just bought another of the mx066 model from ebay auction.... prices start at 0.01 with $6.95 s&h
Got it for 17.65 bid. (its all in the timing of your bid) If at first you don't succeed, try again....
[its the same as the one from bakatronics] {it's a 30 amp unit}
When you mount the board in the box, Its a good idea to separate the pot from the board with a ribbon cable about 3 inches long. It will increase the durability by making the instalation less
succeptible to damage by flexing and vibration. If an aluminum box is used standoffs are available from radioshack. pictures are not on the site yet, but my site is http://waterworks4fuel.com
JT

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12-16-2008 11:37 PM
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JET USA Offline
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RE: where is the best place to a 70-80amp PWM
I drew up a circuit diagram on how I plan to wire my two cells, using two pwm's . I'll try to upload the diagram.
JT

click on the thumbnail image to view. The concept would apply to another cell configuration using a larger ammeter and shunt.
ps:after looking at it again, I think it would be best to connect each pwm positive to the associated cell pos. terminal.
You are welcome to try this.


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"Those who say" " It cannot be done"
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(This post was last modified: 12-18-2008 01:38 AM by JET USA.)
12-18-2008 01:15 AM
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