Relay for bildge pump

[stormalong]

Originally Posted by David Mathis

If reliability is a concern, just get an extra pump and install it near the pump with the reliability concern. Avoid any other related reliability issue by running a separate ground wire to the negative terminal then run a separate wire directly from the positive battery terminal to the switch then to the pump. Now you have no need for a separate relay as the two pumps are on independent systems. This is simpler than adding a relay plus the boat has a second pump. Pumps and wire are cheap.

All Electronics has 40 amp automotive relays foe $2.55 each and sockets for them for $2.25 each. I bought a bunch of them years ago and still have spares. With four installed I may have replaced two relays in the last ten years. You say "pumps and wire are cheap" Cheaper that $5.00 per relay installation? I don't think so.

[Steve DAntonio]

Originally Posted by stormalong

I would agree with you if the float switches and pressure switches on "pleasure boat" grade marine pumps was actually designed and built to handle the loads and electrical transients of the real world. As they are not I will use relays to make up for their shortcomings.

MOVs and other arc suppression solutions also work but be aware that MOVs break down after repeated cycles. They are intended for occasional voltage spikes, not regularly occurring events. https://zerosurge.com/truth-about-movs/

Transients, on small vessel bilge pump systems...not common, at least in the world of 40-80 foot vessels. If you use high quality switches, it's not an issue, nor is reliability. Ultra Safety Systems Ultra Pump Switches are heavy duty, and rated for the current associated with even large 3700 GPH pumps, up to 15 amps. They have a 5 year warranty and in the 20 years I've used them I've had to replace one. There's just no need for relays unless you are talking very long wire runs.

Most of the failed switches I encounter aren't actually a switch issue, they are wiring related.

[rslifkin]

For it's worth, my boat was built with those rolling ball bilge switches of unknown brand. I only have 1 of 3 left due to some changes to my pump setup to reduce standing water, but 34 years later, they work fine. One of the ones I removed cycled regularly for years dealing with ac condensate and stuffing box drips, never had a single issue in the boat's life.