Sain Smart 8 Relay Board

[hebs]

Does anyone know where I can find the exact relay board that centroid use. I have and acorn and Ether1616, all 3 relay boards are identical, however, I have blown 2 individual relays. I tried to desolder the relays to replace the components but they don't want to come off. I have found plenty of sainsmart 8 relay boards (and other brands) but cannot find the exact one that centroid use; with the green removable terminal blocks and the white ribbon socket.

A source in the UK would be ideal. The Acorn CNC Relay Board kit (adapter for older acorn boards) for 40USD shows different connectors to the others.

[Muzzer]

It's unusual to blow a relay (or 2 of them) without damaging the drive circuit, so I assume that's actually where the damage is?

Looks as if Centroid got a custom version made up with ribbon connectors, if indeed it is a Sainsmart product. Even then, there may be other changes (LEDs?).

Can't you cannibalise the components from a Sainsmart board? From what I can see, there's hardly anything there beyond an opto, a switch (FET?), a couple of resistors and a flywheel diode.

Do you have any spare relays (are you using all 8 of them??), in which case you could just move your wiring onto some of the remaining good outputs.

[hebs]

I tried to use the relay to switch on a BLDC motor driver which switch on using centroid then wouldn’t switch off. On investigation, I found that the relay would no longer switch. I thought that it was a faulty relay so moved to another relay and the same happened. It was the driver damaging them. Those relays are now stuck in the activated state even when all power is removed. I have the exact relay component to replace (assuming that it is the relay at fault and not another component) but I cannot desolder them properly. The PCB is double sided meaning that the component pins are soldered all the way through the board. I don’t have a desolder gun and even if I did it would be tricky to remove.

I have all outputs used but I’ve swapped out less important ones for the time being (light & extractor fan).

I may end up paying $50 (inc shipping) for one directly from centroid which seems very excessive.

[tblough]

If you try to switch more current than the relay is rated for, the contacts will weld closed.

[Gary Campbell]

Fractional horsepower and above motors require a contactor, as you have found out, you will blow up the onboard relays.

viewtopic.php?t=4929

[Muzzer]

Ah, if you have been trying to switch the power connection between a PSU and a BLDC driver, you were probably switching a capacitive load - most drivers and PSUs contain fairly sizable DC bus capacitor(s). When you close the relay, you will get a big splat of current on the contacts which can weld them together. If you want to switch the power lines in this way, you need to use a large control relay or contactor. Having said that, why are you wanting to switch the power to the drivers?

[hebs]

Yup, figured out the hard way. 24VDC supply to the driver of a 100w BLDC motor for a small grinder motor (not my spindle motor). Did my maths and got 4.2A so I thought that I was safe (10A max on the relay) - didn’t account for the current surge, basics, doh! I have re-wired and it now works great but I’m down 2 x outputs.

Short of buying a whole new Acorn, surely there must be a way of getting a replacement relay board?

[hebs]

Fractional horsepower and above motors require a contactor, as you have found out, you will blow up the onboard relays.

viewtopic.php?t=4929

Gary, the post you link to: do you have any centroid versions left to sell?

Also, how did you manage to get so many relay boards from centroid? I couldn’t see that they sell them separately?

Thanks

[Gary Campbell]

Gary, the post you link to: do you have any centroid versions left to sell?

Yes there are some left, not sure of the number. Send email to the address listed in the thread for more info.

Also, how did you manage to get so many relay boards from centroid?

One model of controller I used to build uses different relays to save space. The relays came as part of an Acorn kit and were unused. I used to have dozens and dozens of them.