Controlling fuel pumps with solid state relay pwm

ArnyLogan
Posts: 1
Joined: Wed Aug 15, 2018 4:42 pm

Re: Controlling fuel pumps with solid state relay pwm

Post by ArnyLogan »

Hi,...i am a new user here. As per my knowledge with SSR you need to double check how they are wired, I've attached a few different ways and from the look of things there is a requirement for a diode added to the system and permanent earth on one pin, I think this is because there is so little current needed to switch the relay.

seo expert
Last edited by ArnyLogan on Tue Mar 12, 2019 9:02 pm, edited 1 time in total.
Hugh
Posts: 52
Joined: Thu May 19, 2016 7:54 pm

Re: Controlling fuel pumps with solid state relay pwm

Post by Hugh »

Trickster wrote:
I noticed the syvecs manual shows a flyback diode, are these necessary or not?

Graeme
Graeme, from what I understand, when the SSR switches off the current to the fuel pump, the pump continues to rotate and becomes a generator which creates a sudden voltage spike. The current flows in the opposite direction to the way the motor was being driven, so the current spike will hit the SSR and may blow it up.

So my understanding is that is a flyback diode is a necessary safeguard.
stevieturbo
Posts: 991
Joined: Sun Dec 07, 2008 2:04 pm

Re: Controlling fuel pumps with solid state relay pwm

Post by stevieturbo »

Hugh wrote:
Trickster wrote:
I noticed the syvecs manual shows a flyback diode, are these necessary or not?

Graeme
Graeme, from what I understand, when the SSR switches off the current to the fuel pump, the pump continues to rotate and becomes a generator which creates a sudden voltage spike. The current flows in the opposite direction to the way the motor was being driven, so the current spike will hit the SSR and may blow it up.

So my understanding is that is a flyback diode is a necessary safeguard.
It's essentially back EMF. It occurs with any inductive load....which is relays, ignition, anything really. And is exactly where the spark from the coil comes from.

The higher the load when on power, the larger the back EMF when power is removed. So the diode is to allow this current/voltage to dissipate within the motor itself during the off period. This can be hundreds of volts...
And using ignition as a good example, many thousands of volts, but we're actually using this to our benefit to fire the spark.

https://progeny.co.uk/back-emf-suppression/
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