Shownomercy

iTrader: (1)

At the risk of bumping an old thread (ref https://ls1tech.com/forums/forced-in...alone-ems.html) I will just make a new one.

Looking to PWM my fuel pump (4301) so I don't have it cycling 100% at idle etc, but want to prove system out on cooling fans first cause losing a fan is not the end of the world. Is the below image I stole from the internet a valid approach? I have 40amp SSR DD and will be driving em via Holley -pwm

Seems too easy to be right, so has me worried.

LSswap

Yikes, that pump is over $800.

What frequency are you planning to drive it at? Wonder how noisy it will be.

Shownomercy

iTrader: (1)

I was driving em at 300hz, burnt both SSRs open

Round two will have flyback diodes installed and hopefully that does it.

LSswap

I'm no expert on SSRs, but I think your diagram shows the positive battery terminal going to the SSR terminal 1. Terminal 1 is the negative terminal.

badass68

iTrader: (7)

Yep. He’s got it backwards. + should go to battery and - goes to load (pump or fan).

There’s better options for fans though. Oem modules from many gm and Ford vehicles work great.
I’ve used this one many times at 120hz

https://www.ebay.com/itm/Cooling-Fan....m46890.l49292

Shownomercy

iTrader: (1)

Got new SSR's in today, and wired em how the schematic showed that came with em. Switching the negative side of the fan versus how I had em previously switching the hot side. Added in a fly back diode to both and so far so good.

If weather cooperates tmmr, I will drive it and see how they do.

stevieturbo

It is that easy, and the Crydom DC relay should be able to do 300Hz no problem at all. I run mine at 200Hz.

I tested at various frequencies and duties, and that just seemed to offer a little more flow than others.

stevieturbo

Doesn't really matter which side you switch for the load. I switch the 12v side, simply as it's easier to ground the pumps locally and it means when off, there is no live going to the pumps at all.

I've a pair of 450's going, and intend to run a 3rd when needed. Currently on a 60A Crydom, but have a 100A if needed

Forcefed86

iTrader: (4)

Maybe pushing my luck, but I've never had to use the diode or flyback diode when using the standard FOTEK 100A SSR. Used it on alky pumps and fans. Never had an issue. What is the purpose of it? I mean I know what a diode does... just wasn't sure why it was needed. I'm pulsing the ground and not the power, but as mentioned don't know why it would matter.

Shownomercy

iTrader: (1)

I am no EE, but I believe its to allow the energy remaining in motor coils a path to go instead of slamming back into the switch.

Forcefed86

iTrader: (4)

Ah, gotcha... Looking at the diagram I think they are built into the FOTEK SSR maybe? But the diodes look to be on the input not the output circuit? IDK what the coding means on some of the output circuit. Just thinking I might want to toss a diode on my alky pump when I install it in the new project this year, guess it can't hurt anyway!

LSswap

I don't think it matters which side you switch from as long as you don't reverse the polarity to the ssr.

When the PWM goes to zero, the motor becomes a generator and the voltage it generates is opposite the voltage supplied. The solid state components in the ssr can't tolerate a big voltage in the reverse direction. This isn't as much of an issue with motors because the voltage they generate is fairly small. It's a big problem when driving heavy solenoids because their huge number of turns in the coils, generate a high reverse voltage that can wipe out the ssr components.

Yes, not so much slamming, but in reverse polarity.

The diodes you see in that image are on the input side. They are the light Emitting Diodes (LED) that isolate the load from the input. There is no diode on the output side.

stevieturbo

it's already been covered very well in other threads.

This video explains it well.


And a means of suppressing the back EMF IS essential unless all the components in the system have been designed to operate without it, which most SSR's are not.

Basically compare it to what happens in your ignition coil.

12v in....you switch it off and what happens in the windings ? The field collapse causes that build up of energy to release and because of the windings, it is a very very high voltage.

Any inductive load is basically the same, except when you PWM it, you're doing it hundreds, thousands of times per second.

stevieturbo

For my meth pump I just use the little Hella SSR, that's more or less a drop in replacement for a normal relay. It just needs some minor wiring change vs a normal relay, but means you can just plug it into the same relay holder so no ******* about with additional wiring, and it does have flyback protection built in. Although it only handles around 10-13A inductive loads from what I recall.
Still plenty for almost all methanol pumps except the most powerful, and even thing current will very much depend on how hard you're trying to work the pump.

Shownomercy

iTrader: (1)

Going to switch it back to switched hot and I think this is the correct schematic. I am way over thinking this

LSswap

No, still backwards. the #1 terminal has to go to the negative side.

LSswap

Once again, I'm no expert, but this is how I think it needs to go.




from the crydom tech sheet: My corrected version of yours is on the right.

stevieturbo

Correct, load should be in no 1.

Shownomercy

iTrader: (1)

When I had it hooked up with the 1 & 2 switched, it was constant on.

stevieturbo

Some drawings show a 1k resistor across the input side, this may be ecu dependent and may be a cause of yours staying on when you are "off".

ie. I believe this is for some ecu's or setups that behave strange, so that when you power off, both input terminals will be at the same potential...i.e off.

I have tried mine with the Syvecs with and without the resistor without issue, although I left the resistor in place. Because why not ?

This is Haltech's drawing which is pretty clear, with the 12v side PWM'd ( obviously add fuses/protection where needed )