OL Fuel Pump Control Buzzing Relay?

[CMac89]

I had this feature activated and the relay is buzzing; however, it acts normally in on/off mode. I'm guessing that the relay has a minimum current commanded by the PWM table in order for the relay to function properly? Or is there potentially something else going on? Seems like the relay should be on/off until a running condition is satisfied.

This is MS3X 1.4.1 beta 4.

[Matt Cramer]

Open loop fuel pump control should not be used with a conventional relay - it needs a solid state relay to work.

[CMac89]

Uh oh, I see. Same with closed loop?

Seems like it should be a documentation update. Is there an update to be anticipated?

[Matt Cramer]

Both of these are intended to pulse the relay - a conventional relay can't switch fast enough.

[aidandj]

Both of these are intended to pulse the relay - a conventional relay can't switch fast enough.

Any good links for writeups on ss relays?

[tbaggins]

https://en.wikipedia.org/wiki/Solid-state_relay - for general information

http://www.autospeed.com/cms/article.ht ... s&A=112737 - better information on automotive use, pay attention to inductive applications (like a fuel pump), they need an flyback diode.

I intend to use one of these for my fuel pump control module, I used it in a robotics project driving wheel chair motors and it has worked well so far (it is high side switched though, so an output besides the normal fuel pump would have to be used) -
http://www.hessmer.org/blog/2013/12/28/ ... h-arduino/

An example of a good relay that is negative switched (compatible with the fuel pump output on the MS) and has the standard SPST footprint that a normal automotive relay has:
http://www.summitracing.com/parts/hla-h ... /overview/

I have a few solid state relays that I have used, one of them burned out and almost started a fire. I have used them to drive high current hot plates in my chemistry set, as well as to control my smoker using a PID controller without issues though. Generally the higher the relay is rated the better it will perform, as the amp rating goes up, the on state resistance goes down, producing less heat at the same current.

If you buy a puck style SSR (the square ones that usually pop up in a google search), pay attention to AC vs. DC for control and load, as well as current ratings

Edit - added another couple of references

[aidandj]

Awesome writeup. My walbro 400 looks like it will use a max of 21 amps. So that 32 amp relay will work fine. Plan to wire it in with some 10 or 12 gauge wire, and jumping the standard relay under the dash.

EDIT: Looks like the hella is only rated to 20amps continuos. Although i probably won't be pushing it that hard I would rather overbuild.

[tbaggins]

The relay's data sheet says 20 amps continuous and 30 amps peak. Your fuel pump flow vs current draw shows that it only draws 21 amps when it is is pushing 130 psi (http://www.full-race.com/store/images/f ... tent-2.jpg), which I am sure you are not doing. But, if the pump ever seized, it would definitely draw more than this number. I would fuse it at 20 amps if I used it with that pump.

One thing I am curious about with the relay is that it does not have a rating for inductive loads, only resistive. I am not sure if they don't list it because it does not matter what type of load it is, or if it is not made for that.
http://hellahd.com/index.php/default/el ... 931773987/

A puck style solid state relay would work, it is just wired different. I only recommended the hella relay because it has a normal spst relay footprint.

[tbaggins]

This is the brand that all of my solid state relays are that I have used. I actually bought them from this seller, I left a bad review on amazon, and got an email a few weeks later stating that the batch of relays that I had bough from were defective from the factory. The seller refunded my money. It smoked the first time I tried it, so it would be wise to test it under a large current first. Using a proper heat sink is important when using them as well.

http://www.amazon.com/Single-Phase-SSR- ... tate+relay

[CMac89]

Thanks for all of the info!!

I bought some SSRs from ebay and I wired them up. However, they're showing 12V without ground, then when I apply ground, there's no voltage. How should it be wired??

1- : ground (MS3pro fuel pump output) (also tried directly to ground)
2+ : To fuel pump
3+ : 12V switched
4- : engine ground

[tbaggins]

see if this helps:

http://www.jamesobartlett.com/?tag=megasquirt

It seems like your pins are mixed up. I would have to see the relay you are using, can you provide a link? Your fuel pump and megasquirt should not be on the same side. Ground from the megasquirt is on the input side with a 3-32vDC + power supply, and your fuel pump circuit is on the opposite side, the wiring for which depends on how you are driving the fuel pump. The link above should clarify what I am saying.