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Old 18-05-2019, 11:59   #1
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Relay for Autopilot Pump

Hello sailors,

I am about to wire up a new L&S hydraulic ram to our boat. I would rather not run a larger wire to it from the panel, about 60'+ total run, and wondering what relay would be best to do this?

I have bought a 12v SS relay off Amazon for our reefer compressor but it was relatively cheap. (YFFSUN B0753ZTWPH https://www.amazon.com/dp/B0753ZTWPH..._wsf4CbFTAC7P8)

I have a Blue Sea electro mech relay for our windlass but it's 250amp and way overkill. What about a regular Cole Hersey relay? Or an automotive type relay?

I just want something reliable and possibly doesn't draw crazy power so I'm reaching out for some help from the hive. I tried the google search but most results are about relays for the clutch or a smaller pilot driving biggee loads.
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Old 18-05-2019, 12:24   #2
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Re: Relay for Autopilot Pump

There is so much cheap-Chinese crap out there,

just google YFFSUN to see their usual product lines

Always grossly exaggerated ampacity specs, like sometimes 5x actual, so a 100A rated contactor welds shut or burns out at even momentary 20A.

The known-good brands seem crazy expensive but for me on a boat I'd go that way.

The automotive stuff is afaik only OK for tiny currents.

I'm looking too, for 3-5Vdc rated continuous 20+ amp cutoffs controllable from BMS or Arduino, haven't found anything reasonably priced enough to bundle into a LFP powerpak, they all burn out within the first hundred cycles. . .
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Old 18-05-2019, 12:35   #3
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Re: Relay for Autopilot Pump

I think you're going to want to use a 12 volt solid state relay.

https://www.amazon.com/uxcell-ASH-40...gateway&sr=8-5
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Old 18-05-2019, 12:54   #4
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Re: Relay for Autopilot Pump

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Originally Posted by sailorchic34 View Post
I think you're going to want to use a 12 volt solid state relay.

https://www.amazon.com/uxcell-ASH-40...gateway&sr=8-5


How do you wore that thing? Where does the trigger wire go?
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Old 18-05-2019, 13:01   #5
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Re: Relay for Autopilot Pump

Wow if that's a unit known-good via experience by members, fantastic value!

Might even stand up to 20A with a good heat sink!

https://images-na.ssl-images-amazon....SR420,420_.jpg
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Old 18-05-2019, 13:08   #6
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Re: Relay for Autopilot Pump

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How do you wire that thing? Where does the trigger wire go?
https://electronics.stackexchange.co...troller-to-ssr
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Old 18-05-2019, 13:09   #7
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Re: Relay for Autopilot Pump

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How do you wore that thing? Where does the trigger wire go?
For an autopilot you need to use two. And depending upon how it's internally constructed you might need a diode on each one. One is wired straight with plus to plus and minus to minus with the other wired backwards. Probably would not need a diode but if it messed up adding a diode to each plus side of the relay would most likely stop any crosstalk.

heatsinks may be required.
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Old 18-05-2019, 13:18   #8
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Re: Relay for Autopilot Pump

If using TTL logic, say with a home-brewed autopilot control head, the robot shop has a nice 13 amp continuous 30 amp intermittent motor H Bridge that's using the low amp TTL logic from say a Raspberry Pi or similar for not much money. That's what I used for my little home-brewed autopilot. it probably has enough capacity to run a linear actuator under deck
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Old 18-05-2019, 13:19   #9
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Re: Relay for Autopilot Pump

If it is running an autopilot ram, I assume you actually need a motor reversing relay. You'll want one that is solid state, because it will accumulate LOTS of operating cycles, and you'll want minimum power consumption by the relay coils.

Skip looking at Amazon. They have cheap Chinese junk. You might find something in one of the industrial sections of ebay, but not unless you know what you really want.

You want something like a Crydon D53TP50D. Select the exact part number to match your needs based on amp draw and voltages used. I used one of these to connect a high amp draw hydraulic ram to a AP controller than had a lower amp rating, but was otherwise fully functional. Worked great.
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Old 18-05-2019, 13:26   #10
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Re: Relay for Autopilot Pump

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I think you're going to want to use a 12 volt solid state relay.

https://www.amazon.com/uxcell-ASH-40...gateway&sr=8-5
How do you think it would compare to something like this?

https://express.google.com/u/0/produ...479468_6480675

Robust longevity under abusively high amp conditions is more important to than price.

My understanding is the mechanical ones from known good makers would be better than cheap Chinese DSS relays
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Old 18-05-2019, 13:30   #11
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Re: Relay for Autopilot Pump

Mechanical relays are not designed for the duty cycle required by an autopilot. The contacts will get pitted and wear out really quickly. That's why solid state as the only way to go for an autopilot. One could add a capacitors across the downstream side. That would reduce but not eliminate contact pitting. Much like the points in an old car.
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Old 18-05-2019, 14:02   #12
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Re: Relay for Autopilot Pump

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How do you think it would compare to something like this?

https://express.google.com/u/0/produ...479468_6480675

Robust longevity under abusively high amp conditions is more important to than price.

My understanding is the mechanical ones from known good makers would be better than cheap Chinese DSS relays
You are an order of magnitude cheaper than what you need.

This is an automotive relay designed to turn on lights, or windshiled wipers. Probably has a MCBF of 100,000 or so. Enough to last 50 years in a car.

If your autopilot pump turns on once a second, this would last you about one day...
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Old 18-05-2019, 14:31   #13
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Re: Relay for Autopilot Pump

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Originally Posted by sailorchic34 View Post
I think you're going to want to use a 12 volt solid state relay.

https://www.amazon.com/uxcell-ASH-40...gateway&sr=8-5
Great, thanks! This will be to power the Pelagic auto pilot, I guess I didn't think about my question long enough. It's jus to turn on the pilot computer which will drive the pump so it will be 20-30amps and I didn't want that long of a run with large wires. I have another heat sink I can use for this as well for heat management. I believe I have a uxcell ssr for my battery charger for BMS cutoff, but its AC. Would you reccomend that 40A one so it's not running near full load at times?
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Old 18-05-2019, 14:33   #14
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Re: Relay for Autopilot Pump

Sorry for the confusion in my original post, it's not for the pump but for the whole pilot system. So basically when I turn my breaker on it turns the relay on to turn on the Pelagic autopilot which in turn powers the hydraulic pump/ram. I was clearly not thinking earlier. So this would be a turn it on and it stays on kind of relay, not one for switching the pump on/off.
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Old 18-05-2019, 15:04   #15
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Re: Relay for Autopilot Pump

Yes my use case is also not millions of duty cycles, maybe a dozen per day maximum.

Thanks for the insights. While I've got you,

if a contactor is rated for Y amps at X Vdc,

does going to lower volts or higher volts potentially mean you might be pushing the ampacity limits?

For example if rated 40A at both 12 and 24 Vdc, but my current is actually

A. 2-5Vdc

or maybe

B. 48-60Vdc

which direction is more stressful to the relay, keeping current at say 30A, but it's a uxcell not crydon unit
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