Water System Problems

[Dockhead]

OK, so, in the absence of instruction from the EE's of the forum, this electrical numpty has had to attempt to educate himself.

I'm a bit torn here between not wanting to go down a long rabbithole with this when I have so much other stuff to do on the boat, and enjoying learning for its own sake -- one of the things I love about cruising.

This resource seemed to be understandable at my numpty level: https://www.newark.com/pdfs/techarti...YourRelays.pdf

I've already learned a very good little piece of information:

"When you are switching a motor load, typical industry practice is to derate [the relay] to 20 percent of the resistive rating."

Knowing (even with my numpty level knowledge) something about inrush currents, I had guessed already that something like this would be appropriate.

Jabsco gives us precious little info about the electrical properties of their pumps, but they do say that the Par Max 4 draws 3 amps @24v and needs a 7 amp fuse.

So I guess that means that the continuous load will not exceed 7 amps, so a 40 amp solid state relay would be just about right, a bit more than 5x. And that's what I bought.

Drawback of an overrated SS relay seems to be voltage drop in the load circuit -- up to 1v, which implies power loss. I don't think this is a big deal. The cited resource recommends SSRs for this application.

The literature with the relay I bought says this:



This resource -- https://www.plantengineering.com/art...de-and-rating/ --

Seems to say that the flyback diode should be rated for 10x the nominal voltage of the protected circuit, so 240v, and 10x the average current, which in my case would be something like 40a.

Sounds like Schottky diodes are the preferred type.

[s/v Jedi]

Originally Posted by Dockhead

OK, so, in the absence of instruction from the EE's of the forum, this electrical numpty has had to attempt to educate himself.

I'm a bit torn here between not wanting to go down a long rabbithole with this when I have so much other stuff to do on the boat, and enjoying learning for its own sake -- one of the things I love about cruising.

This resource seemed to be understandable at my numpty level: https://www.newark.com/pdfs/techarti...YourRelays.pdf

I've already learned a very good little piece of information:

"When you are switching a motor load, typical industry practice is to derate [the relay] to 20 percent of the resistive rating."

Knowing (even with my numpty level knowledge) something about inrush currents, I had guessed already that something like this would be appropriate.

Jabsco gives us precious little info about the electrical properties of their pumps, but they do say that the Par Max 4 draws 3 amps @24v and needs a 7 amp fuse.

So I guess that means that the continuous load will not exceed 7 amps, so a 40 amp solid state relay would be just about right, a bit more than 5x. And that's what I bought.

Drawback of an overrated SS relay seems to be voltage drop in the load circuit -- up to 1v, which implies power loss. I don't think this is a big deal. The cited resource recommends SSRs for this application.

The literature with the relay I bought says this:

Attachment 286181

This resource -- https://www.plantengineering.com/art...de-and-rating/ --

Seems to say that the flyback diode should be rated for 10x the nominal voltage of the protected circuit, so 240v, and 10x the average current, which in my case would be something like 40a.

Sounds like Schottky diodes are the preferred type.

I have a hard time following you and think you are on the wrong path.

I thought you had bought replacement parts to fix the pumps, in which case you only need to put the new part in and you’re done.

But now you seem back to using a relay that I assume is controlled by a pressure switch. First of all, your pump. No, it’s continuous current draw is 3A, not 7A. The 7A fuse value is an indication of inrush current. So where your math concludes 40A it is less than half that.

Also, the voltage drop over a SSR is a big deal. A huge deal. Have you not seen the required heat sinks that you are supposed to buy and mount to the SSR as well?

For lifespan of parts it is hard to improve over the lifespan of a mechanical relay and usually it is better to simply replace the relay periodically. While a capacitor normally outlives a relay (today’s low quality may not!) it is not likely to outlive a relay that it protects as part of a snubber circuit. This means you still have the failures but now it’s the capacitor and while replacing that, which is much more costly, you also have to replace the relay because not doing so risks another outage soon after.

If you burn up micro switch contacts in a pump and are sick of buying or repairing the pump then maybe buying a better pump is not only the logical step forward but also the one that is least involved.

What I find much more important is improving access, simplifying replacement (use Anderson connector for electrical hookup), increasing performance (flexible connectors) and availability (redundancy, two pumps) rather than trying to improve a mediocre pump.

[rslifkin]

Look up the full datasheet for the Jabsco pumps. They usually give a power draw vs output pressure graph.

I'm running the Jabsco Hotshot HD4 as a fresh water pump (basically the same pump as the Parmax without the internal bypass). My 12v version is listed as requiring a 20A fuse (although I have it on the 15A breaker that was there for the water pump already and it has never tripped it). Max current draw is listed as 11 amps at 60 psi, and it'll only draw that right at the end of the cycle before shutting off. Looking at the graph in the datasheet, power draw when it cycles on at 40 psi should be about 9.5 amps.

In my experience with the Jabsco pump, the pressure switch is a definite weak point, although adding a relay seems to stop them from burning up (and the pressure switch wiring is all external, so adding the relay is a 5 minute job). The actual pump has been solid for me. Unlike some pumps I've used, I can drain the entire water tank through it at the end of the season without hitting the thermal cutoff on the pump. It's not overly loud (although certainly not silent), and the mechanical parts of the pump have been reliable. It has good performance at high pressure as well, which is why I picked it. Compared to some of the Shurflo and others I looked at the flow rates in the 40 - 60 psi range are noticeably better for the same rated open flow, which likely points to a beefier motor on the pump (and therefore less loss of speed as output pressure climbs). That was a big factor for me, as I'm running my system with a 60 psi cut-out, 40 psi cut-in pressure range.

For the Jabsco pumps, personally I think the Hotshot series is more suitable for use with a pressure tank. The Parmax will take longer to reach full pressure (and waste power) as the internal bypass starts to open before cutoff pressure is reached. The bypass on the Parmax is intended to avoid the need for a pressure tank, as it will tolerate much lower flows before cycling. That said, the original setup on my boat got perfectly good lifespan from plain on/off (no bypass) 1980s era Shurflo pumps with no pressure tank at all, the pump just cycled to its heart's content at low flow rates (which was annoying, but didn't seem to hurt anything).

It's only a concern in some setups, but as attractive as the Marco pumps look, they're significantly more limited in output pressure (most I've seen are limited to 35 - 40 psi). Plus they're quite a bit more expensive, although not having used one personally, it's entirely possible the performance and lifespan justifies the higher cost.

[Dockhead]

Originally Posted by s/v Jedi

I have a hard time following you and think you are on the wrong path.

I thought you had bought replacement parts to fix the pumps, in which case you only need to put the new part in and you’re done.

But now you seem back to using a relay that I assume is controlled by a pressure switch. First of all, your pump. No, it’s continuous current draw is 3A, not 7A. The 7A fuse value is an indication of inrush current. So where your math concludes 40A it is less than half that.

Also, the voltage drop over a SSR is a big deal. A huge deal. Have you not seen the required heat sinks that you are supposed to buy and mount to the SSR as well?

For lifespan of parts it is hard to improve over the lifespan of a mechanical relay and usually it is better to simply replace the relay periodically. While a capacitor normally outlives a relay (today’s low quality may not!) it is not likely to outlive a relay that it protects as part of a snubber circuit. This means you still have the failures but now it’s the capacitor and while replacing that, which is much more costly, you also have to replace the relay because not doing so risks another outage soon after.

If you burn up micro switch contacts in a pump and are sick of buying or repairing the pump then maybe buying a better pump is not only the logical step forward but also the one that is least involved.

What I find much more important is improving access, simplifying replacement (use Anderson connector for electrical hookup), increasing performance (flexible connectors) and availability (redundancy, two pumps) rather than trying to improve a mediocre pump.

Capacitor? Where does a capacitor figure in this? I lost you.

[Dockhead]

Originally Posted by rslifkin

Look up the full datasheet for the Jabsco pumps. They usually give a power draw vs output pressure graph.

I'm running the Jabsco Hotshot HD4 as a fresh water pump (basically the same pump as the Parmax without the internal bypass). My 12v version is listed as requiring a 20A fuse (although I have it on the 15A breaker that was there for the water pump already and it has never tripped it). Max current draw is listed as 11 amps at 60 psi, and it'll only draw that right at the end of the cycle before shutting off. Looking at the graph in the datasheet, power draw when it cycles on at 40 psi should be about 9.5 amps.

In my experience with the Jabsco pump, the pressure switch is a definite weak point, although adding a relay seems to stop them from burning up (and the pressure switch wiring is all external, so adding the relay is a 5 minute job). The actual pump has been solid for me. Unlike some pumps I've used, I can drain the entire water tank through it at the end of the season without hitting the thermal cutoff on the pump. It's not overly loud (although certainly not silent), and the mechanical parts of the pump have been reliable. It has good performance at high pressure as well, which is why I picked it. Compared to some of the Shurflo and others I looked at the flow rates in the 40 - 60 psi range are noticeably better for the same rated open flow, which likely points to a beefier motor on the pump (and therefore less loss of speed as output pressure climbs). That was a big factor for me, as I'm running my system with a 60 psi cut-out, 40 psi cut-in pressure range.

For the Jabsco pumps, personally I think the Hotshot series is more suitable for use with a pressure tank. The Parmax will take longer to reach full pressure (and waste power) as the internal bypass starts to open before cutoff pressure is reached. The bypass on the Parmax is intended to avoid the need for a pressure tank, as it will tolerate much lower flows before cycling. That said, the original setup on my boat got perfectly good lifespan from plain on/off (no bypass) 1980s era Shurflo pumps with no pressure tank at all, the pump just cycled to its heart's content at low flow rates (which was annoying, but didn't seem to hurt anything).

It's only a concern in some setups, but as attractive as the Marco pumps look, they're significantly more limited in output pressure (most I've seen are limited to 35 - 40 psi). Plus they're quite a bit more expensive, although not having used one personally, it's entirely possible the performance and lifespan justifies the higher cost.

I like the Marco pump, which looks to me like a superior unit.


But I have two perfectly good pumps which only have bad pressure switches so I think I'm going to go in that direction.


The weak point seems to be the pressure switch contacts (failed on both pumps), so that's why I will use a relay.

[s/v Jedi]

Originally Posted by Dockhead

Capacitor? Where does a capacitor figure in this? I lost you.

I brought that up on autopilot… maybe wrong but often to limit inrush, like soft start, capacitors are used.

[Dockhead]

Originally Posted by s/v Jedi

I brought that up on autopilot… maybe wrong but often to limit inrush, like soft start, capacitors are used.

Ah, OK.


In this application, it looks like a flyback DIODE is needed. According to what I read, 10x nominal voltage (so 240v) and 10x average current (so 60a or so).


Because the water pump is an inductive load.

[s/v Jedi]

Originally Posted by Dockhead

Ah, OK.


In this application, it looks like a flyback DIODE is needed. According to what I read, 10x nominal voltage (so 240v) and 10x average current (so 60a or so).


Because the water pump is an inductive load.

Correct but I think it will be in the pump already.

[Dockhead]

Originally Posted by s/v Jedi

Correct but I think it will be in the pump already.

Hadn't thought of that! Hot tip; thanks. I'll write to Jabsco, I guess.