PWM 30 amp burn fuse @ 20 amp

[u4david]

OK I got it wired just like the plan shows.(PICTURE)Positions/order of gauge- or relay-or fuse may be in different order but all is on the "live" circuit
My fuse is 30 amp.Whole system is 30 amp rated minimum as most is build over kill.
I have 30 am automotive gauge.
Cell works and tested.

After 10 minutes of 20 amp draw (driving down the road)the fuse goes out.
I tested what I could.
I seems to not the find the problem.

Could be the pwm.
Could be inaccurate reading of pulsed amps?
I know the gauge is accurate with out the pwm.

Is there a chance that the amp gauge reads the pulsed amps differently than straight amps would?

What could be the issue that I burn 30 amp fuze when gauge shows steady 20 amp?

[Painless]

I would certainly hold judgement on this until one of the electronics gurus pipes in, but here is my theory.
The PWM will try to maintain an AVERAGE current of 20 amps, however, when it pulses the cell will pull whatever the catalyst concentration allows. Let's say for example that your catalyst strength would pull 40 amps without the PWM, the PWM would then only allow pulses timed to operate the cell 50% of the time, creating an average pull of 20 amps.

I believe this is why your fuse is blowing, also, your ammeter will only show an average due to the speed of the pulses.

Your best answer would probably be a slower blowing fuse.

[ridelong]

I agree with PAINLESS.
Try a slow blow fuse.

[u4david]

I think it hit me as I look at the picture.My amp is instaled on PWM output circuit.But it needs to be pwm power supply.
Will rewire and check back.

[ridelong]

u4david,

The ammeter should read the same on either place.

Use a slow blow fuse or measure the current with the pwm full on and use a fuse 1 size larger than the measurement.

[u4david]

I think that pwm draws constant current and it converts it to pulsed current.


Or not?It could function as fast switch?(100mhz)

How the pwm manages the current?


How slow burning fuse is different from regular?
If regular 30 amp fuse burns does that mean that the protection limit is exceeded.So wouldn't slow burning fuse bring my circuit at risk of damage?

In the case of slow blow.Shuld i be using 25 amp slow blow vs 30 amp fast blow?

[ridelong]

A pulse width modulator (PWM) is a device that turns a circuit full on or full off.

The amount of on time is called the duty cycle. if a pwm is at 50% duty cycle it is on 1/2 the time and off 1/2 the time. That is how they control average current. If a load draws 10 amps at 12 volts, installing a pwm running 50% duty cycle at 12 volts would reduce the average current to 5 amps.

A slow blow fuse is made to allow transients larger than the fuse rating for short periiods. As long as the AVERAGE current is less than the fuse rating it will not blow.

[u4david]

http://www.bakatronics.com/shop/item.aspx?itemid=581

DUTY CYCLE 0-100
FREQUENCY 100 MHZ

wHAT THIS MEANS?aND WHAT WOULD BE THE BEST FUSE TO PROTECT THIS,AND ALSO HOW TO ACURATLI MEASURE THE AMPS ON THE CIRCUIT TO SE WHAT I DRAW?

[ridelong]

u4david,

The 100 hz means the pwm cycles 100 times per second (.01 second).

The duty cycle 0-100 means you can turn it off (0), or you can turn it full on (100). If you adjust it to 50, it will be on .005 seconds and off .005 seconds.

Use a slow blow fuse.

Any decent digital meter will accurately measure average current for the 100 hz..

[u4david]

so if ystem is build for actual 30 amp.
When i will run it at average 30 amp that will mean that the sytem have current flow sometimes 0 an sometimes 60 amps= average 30 amp?

In tis case some wires will get hot or melt contacts when current of 60 amps is in progress?

I can already ell that some wires have heat build up.And they are rated higher tat 30 amp.I check the connection make suer it is not outcome of bad contact.