Aqua rite varistor blown out

[D.Douglas]

Hello,
I am trying to find out what would cause the blue varistor on the aqua rite main circuit board to blow out? It is the bottom blue varistor that blows out. Does anyone know what would cause this to happen? Your help is greatly appreciated.

 

[ajw22]

Welcome to TFP.

From Hayward Aquarite SWG - Further Reading

There are two V150LA2P, VARISTOR 240V 1.2KA, made by LittelFuse as the primary line of defense against transient or voltage spike. They are connected in series, across L1 & L2 when configured for the 220V operation. Alternatively, the two are in parallel across L1 & Neutral for the 120V configuration. If the AC power is applied to TB1, the MOV's are "HOT" and susceptible to voltage spike even if the inductance Transformer and any of its wire is loose or not properly connected to the board. And no way, for any downstream components to induce voltage spike or sags back to the MOV's.

MOVs are often connected in series with a thermal or line-fuse, so that the fuse disconnects before catastrophic failure can happen. The initial failure mode of an MOV is always a short circuit in an attempt to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. And that is why it should be preceded by a series fuse. If the fuse isn't there and there's enough energy available to cause the MOV to melt/explode the final failure mode will be an open and the downstream circuitry will then be subjected to the transient causing the open or to future transients which will then cause questions to be asked about whether the downstream circuitry will fail open or shorted. MOV's have a finite life expectancy and "degrade" when exposed to a few large transients, or many small transients. As a MOV degrades, its triggering voltage falls lower and lower.

As to the AQR board, Hayward disregarded the line fuse before the MOV's. The upstream local circuit breaker has no function related to disconnecting an MOV. So what's the MOV in the AQR board for and how are they going to protect your main board? Well, it's more like of a visual notification for me! If it torched itself and went up in smoke then that's a good indication that the MOV took the hit. The AQR will continue to chlorinate even with all the smoke and fire going on until the MOV's vaporized and you may not even notice anything unusual until the next time you inspect the board.

 

[D.Douglas]

Thank you so much for your reply. Unfortunately this happened within 6 months of installation that I noticed. The salinity readings on the digital display let getting lower and lower to the point that it read 1400 ppm compared to my manual testing of 3600 ppm. When I replace the main board, within 24 hours, the varistor had blown again. I am at a loss for why this might be happening and I don’t want to install a new board without pin pointing the issue and resolving it first.

 

[ajw22]

Post a pic of both sides of the board.

Is it wired to 120V or 240V?