Big Blue's Transformation

[ArdWrknTrk]

I'm now finding some relays. For reference the HF compressor is rated at 1.5 HP but is said to pull a max of 14 amps.

• Yeeco 30A: This says 30A at 250VAC, but then it says 1HP at 110VAC. Sorry, but 30A @ 250V is 7500W, which is technically about 10 HP. I'm lost.

• Jameco: This one is rated at 2HP @ 250VAC, and 30A @ 250VAC.

I'm trying to remember what I've learned about inductive motors, starting current, etc. Someone want to school me?

You need to look for a contactor.

These are used by machines that have a low voltage control circuit to switch AC voltage.

Often 3 phase at something like 408V, but we all know that for you there's no kill like overkill.

Old fashioned boilers also used thermostats to control line voltage circulators.

But I don't know if one of those relays could handle two horsepower.

[Gary Lewis]

You need to look for a contactor.

These are used by machines that have a low voltage control circuit to switch AC voltage.

Often 3 phase at something like 408V, but we all know that for you there's no kill like overkill. http://www.garysgaragemahal.com/uploads/6/5/8/7/65879365/laughing-25-x-25_orig.gif

Old fashioned boilers also used thermostats to control line voltage circulators.

But I don't know if one of those relays could handle two horsepower.

Jim - Thanks. Contactor is a good term. But in this case I'm not looking for serious overkill. Just adequate. But I'm trying to remember how to determine what is adequate. IOW, is a 2 HP @ 250VAC rating just 1 HP @ 120VAC? Or is it still 2 HP? I know doubling the voltage at the same current usually doubles the HP rating of a motor, but is there a parallel on contactors/relays?

Scott - Thanks for the pic and data sheet via text. The pic of the one on ebay, below, makes it look huge. But looking at the data sheet I see that the module is only 1 3/4" x 2 1/4", so I'm guessing that heat sink is only 4" square.

What I think I need to do is to is to put a box in the space above the inverter, and include in it the contactor/relay, a single AC outlet for the compressor, a fuse, and several DC power ports. I'll run 12v from the switch in the dash down the area below the threshold to the relay, and the 110V cord to the compressor through the back of the cab corner into the bed and then into the tool box to the compressor.

Given the limited space above the inverter, I think the power ports will have to point up or anything plugged into them will hit the seatback. And while I'd hoped to also put a power strip up there to make plugging wall warts in for charging things, I'm afraid they'll just have to plug into the inverter itself.

[Gary Lewis]

Jim - Thanks. Contactor is a good term. But in this case I'm not looking for serious overkill. Just adequate. But I'm trying to remember how to determine what is adequate. IOW, is a 2 HP @ 250VAC rating just 1 HP @ 120VAC? Or is it still 2 HP? I know doubling the voltage at the same current usually doubles the HP rating of a motor, but is there a parallel on contactors/relays?

Scott - Thanks for the pic and data sheet via text. The pic of the one on ebay, below, makes it look huge. But looking at the data sheet I see that the module is only 1 3/4" x 2 1/4", so I'm guessing that heat sink is only 4" square.

What I think I need to do is to is to put a box in the space above the inverter, and include in it the contactor/relay, a single AC outlet for the compressor, a fuse, and several DC power ports. I'll run 12v from the switch in the dash down the area below the threshold to the relay, and the 110V cord to the compressor through the back of the cab corner into the bed and then into the tool box to the compressor.

Given the limited space above the inverter, I think the power ports will have to point up or anything plugged into them will hit the seatback. And while I'd hoped to also put a power strip up there to make plugging wall warts in for charging things, I'm afraid they'll just have to plug into the inverter itself.

Ok, with a bit more searching, and a cup of Starbucks, I think I'm starting to come out of the fog. And I think what I'm seeing is that there is no direct correlation between voltage and HP rating for contactors.

The table below, taken from Jameco, shows that some Tyco contactors have a rating of 1HP @ 120VAC and 2HP @ 250VAC, while others are rated at 1.5HP @ 120 and 2HP @ 250. The 1.5HP rating is what I'm looking for, but now if I can figure out all of the other bits in the part number, and that will let me know the sizes. Man, this is complex!

Scott - The Crydom document doesn't mention the terms "HP", "horse", or "inductive". So while that relay says it is good for 50A, that is apparently a resistive load rating. This article at Digikey discusses solid state relays and inductive loads, which includes motors, and says:

"However, designers need to be aware that zero-crossing SSRs may not be able to turn off with highly inductive loads. To account for this, SSR vendors also offer so-called random-switching SSRs that turn on/off at the instant called for by the input transition."

I'm not enough of an electronics engineer to know what kind of SSR the Crydom one is, and the fact that it doesn't discuss inductive loads suggests to me that it isn't designed for them.

[kramttocs]

Ok, with a bit more searching, and a cup of Starbucks, I think I'm starting to come out of the fog. And I think what I'm seeing is that there is no direct correlation between voltage and HP rating for contactors.

The table below, taken from Jameco, shows that some Tyco contactors have a rating of 1HP @ 120VAC and 2HP @ 250VAC, while others are rated at 1.5HP @ 120 and 2HP @ 250. The 1.5HP rating is what I'm looking for, but now if I can figure out all of the other bits in the part number, and that will let me know the sizes. Man, this is complex!

Scott - The Crydom document doesn't mention the terms "HP", "horse", or "inductive". So while that relay says it is good for 50A, that is apparently a resistive load rating. This article at Digikey discusses solid state relays and inductive loads, which includes motors, and says:

"However, designers need to be aware that zero-crossing SSRs may not be able to turn off with highly inductive loads. To account for this, SSR vendors also offer so-called random-switching SSRs that turn on/off at the instant called for by the input transition."

I'm not enough of an electronics engineer to know what kind of SSR the Crydom one is, and the fact that it doesn't discuss inductive loads suggests to me that it isn't designed for them.

This is an interesting topic - following along and digesting. Haven't researched these beyond a casual look at them from an arduino perspective and that didn't deal with HP or loads like a compressor. Shame the crydom won't work - the design looked more like something to survive in an automotive application than some of other (ice cube) ones I found.

[Gary Lewis]

This is an interesting topic - following along and digesting. Haven't researched these beyond a casual look at them from an arduino perspective and that didn't deal with HP or loads like a compressor. Shame the crydom won't work - the design looked more like something to survive in an automotive application than some of other (ice cube) ones I found.

I can't say that the Crydom unit won't work, but the fact that it didn't list inductive load spec's makes it very suspect.

I'm heading out to the shop soon and will see how much space I think I have and if one of the Tyco contactors will fit in it. If so I'll pick one that has the needed capacity to handle the compressor and let y'all know.

[ArdWrknTrk]

Jim - Thanks. Contactor is a good term. But in this case I'm not looking for serious overkill. Just adequate. But I'm trying to remember how to determine what is adequate. IOW, is a 2 HP @ 250VAC rating just 1 HP @ 120VAC? Or is it still 2 HP? I know doubling the voltage at the same current usually doubles the HP rating of a motor, but is there a parallel on contactors/relays?

Scott - Thanks for the pic and data sheet via text. The pic of the one on ebay, below, makes it look huge. But looking at the data sheet I see that the module is only 1 3/4" x 2 1/4", so I'm guessing that heat sink is only 4" square.

What I think I need to do is to is to put a box in the space above the inverter, and include in it the contactor/relay, a single AC outlet for the compressor, a fuse, and several DC power ports. I'll run 12v from the switch in the dash down the area below the threshold to the relay, and the 110V cord to the compressor through the back of the cab corner into the bed and then into the tool box to the compressor.

Given the limited space above the inverter, I think the power ports will have to point up or anything plugged into them will hit the seatback. And while I'd hoped to also put a power strip up there to make plugging wall warts in for charging things, I'm afraid they'll just have to plug into the inverter itself.

Gary,

1 HP = 746W.

You have a 3,000W inverter, so I would think you want a relay rated for 4 horsepower continuous.

[kramttocs]

I can't say that the Crydom unit won't work, but the fact that it didn't list inductive load spec's makes it very suspect.

I'm heading out to the shop soon and will see how much space I think I have and if one of the Tyco contactors will fit in it. If so I'll pick one that has the needed capacity to handle the compressor and let y'all know.

Crydom was just a random one I found last night so know nothing about them but out of curiosity I called their tech line and he agreed it wasn't right for this case. He suggested the CWD2490-10. It's up to 2.2HP.

[Gary Lewis]

Crydom was just a random one I found last night so know nothing about them but out of curiosity I called their tech line and he agreed it wasn't right for this case. He suggested the CWD2490-10. It's up to 2.2HP.

Jim - I don't plan to run any bigger motor than the 1.5 HP one on this compressor. And since size and expense seem to go hand in hand with capacity, I just want one that can handle this compressor and a few wall warts.

Scott - Thanks for calling them. But the CWD2490-10 is $100 at Digikey. It is small at 1.75" x 2.25", but does it require a heat sink? I'll have to read more.

[kramttocs]

Jim - I don't plan to run any bigger motor than the 1.5 HP one on this compressor. And since size and expense seem to go hand in hand with capacity, I just want one that can handle this compressor and a few wall warts.

Scott - Thanks for calling them. But the CWD2490-10 is $100 at Digikey. It is small at 1.75" x 2.25", but does it require a heat sink? I'll have to read more.

Yikes. I didn't check the price. So how's that Tyco one looking?

[ArdWrknTrk]

Yikes. I didn't check the price. So how's that Tyco one looking?

Surplus City has some Heartland Controls 30A 2 pole contactors.

40A max rated for 600V

2 1/8 x 3 1/4"

MADE IN CHINA

They are not takeoffs.

$4.50 each.