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Old 01-06-2016, 17:57   #1
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Suitable relay for larger Condensor fan

I've got an Isotherm refrigerator with a BD35F compressor. The install is less than ideal regarding compressor placement so I am planning on adding a ducted air supply to feed cabin air to the condensor. However to do this I feel like I'll need to install a fan that draws .3-.5 amps and don't want to overload the control module.

What I was thinking of doing was removing the existing muffin fan from between the coils, then using the output of the control module to switch a solid state relay like this DC60S3 - 60 VDC, 3 Amp, DC Control Solid State Relay (SSR) to power the new fan.

Will this work without causing the module to think the fan is an open circut?

I was looking at a standard bosch type relay but I don't wan't the added power consumption from driving the latch coil the entire time the fan is running.

What is the general feeling about this? Do i need the relay? Will the relay I've selected work with minimal parasitic consumption of precious amps?
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Old 01-06-2016, 21:24   #2
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Re: Suitable relay for larger Condensor fan

Serious overkill, not to mention about a half a volt voltage drop across the semiconductor junction.
I'm not sure you even need a relay, but you could certainly get by with a smaller sized one.
The fridge circuitry will handle up to an amp if I remember correctly, but check your documentation.
If you do decide to add to the original works, first find a fan that meets your needs then get a relay which will handle the fan current.
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Old 02-06-2016, 06:02   #3
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Re: Suitable relay for larger Condensor fan

The reason for the relay is that the compressor controller is rated for 1/2 amp max, with "a higher current" allowed for 2 seconds at startup.

However I had missed that little gem about the voltage drop across the semiconductor. Scratch the ssr......

Ok, so I'll move to a smaller relay, unless someone can say with some authority that running a larger fan pulling a 1/2 amp continuously through the controller won't create another set of problems regarding heat failure.


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Old 02-06-2016, 06:54   #4
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Re: Suitable relay for larger Condensor fan

Danfoss BD35 and BD50 compressors are electrically protected from failures by a series of safety circuits the fan circuit F- and small Plus + modules terminals are but one of these boot up and run safety devices. If this fan circuit sees a current higher than 500 milliamps (1/2 amp) compressor will be prevented from running. If the condenser fan is drawing too much current control module assumes poor compressor cooling and stops compressor. Water cooled Danfoss powered systems do not have this compressor protection feature.

If a second fan is to be added to run at the same time as condenser fan a relay control activated in parallel by a few milliamps keeping the fan circuit terminals Small+ and F under amp at 12 volts is used. Power to relay contacts must be fused. If this Danfoss BD compressor is operated by a 12/24 volt AC/DC special converter Module will be operating on 24 volts while fans will still be powered by 12 volts.

If you do not want the relay use a inexpensive snap action switch activated by heat see FANS section on my web site.
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Old 02-06-2016, 10:46   #5
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Re: Suitable relay for larger Condensor fan

This ought to do it for you.
Only 16 milliamp coil draw with a six amp switching capacity.

2903371 Phoenix Contact | Relays | DigiKey
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Old 02-06-2016, 11:47   #6
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Re: Suitable relay for larger Condensor fan

Quote:
Originally Posted by senormechanico View Post
This ought to do it for you.
Only 16 milliamp coil draw with a six amp switching capacity.

2903371 Phoenix Contact | Relays | DigiKey

Thanks, it's almost exactly what I'm looking for (the rail mount isn't quite to my liking, but if it's what I get, it's what I get). I'm beating my head on a wall trying to find coil current for most of the Bosch relays or micro relays I've looked at!!!


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Old 02-06-2016, 12:07   #7
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Re: Suitable relay for larger Condensor fan

These guys take 8mA and will handle 1A:http://www.amazon.com/Electronics-Sa.../dp/B015GN83I6
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Old 02-06-2016, 12:09   #8
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Re: Suitable relay for larger Condensor fan

Quote:
Originally Posted by senormechanico View Post
This ought to do it for you.
Only 16 milliamp coil draw with a six amp switching capacity.

2903371 Phoenix Contact | Relays | DigiKey
And as an aside, i feel like a kid in a candy store with the digikey website!!!
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Old 02-06-2016, 12:57   #9
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Re: Suitable relay for larger Condensor fan

You can buy this relay on Ebay for $5 (or $1.50 ea in lots). Coil uses almost no power, contacts are rated 40 amps NO and 30 amps NC.
I use them all over the boat. You probably have one or more in your car.
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Old 02-06-2016, 16:52   #10
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Re: Suitable relay for larger Condensor fan

Quote:
Originally Posted by Lepke View Post
You can buy this relay on Ebay for $5 (or $1.50 ea in lots). Coil uses almost no power, contacts are rated 40 amps NO and 30 amps NC.
I use them all over the boat. You probably have one or more in your car.
I've got those coming out of my ears, but the coil current is a little too much for what I want to do. I hooked one of the Hella brand up in the garage and it's coil was pulling 300ma from a battery to close the contacts. Not bad but more than I want to add as a parasitic load to the already hungry refrigerator.
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Old 02-06-2016, 17:05   #11
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Re: Suitable relay for larger Condensor fan

I connected a high efficiency computer fan directly to my BD35 output terminal to expel air from the closed cabinet it's located in. No need to pump out more air than the unit heats up. From memory that fan draws around .13 amps @ 12VDC.

And on that note, you should draw air from an enclosure rather than pump air in whenever possible. This reduces dust, and quite possibly moisture, build up inside the cabinet. If you expel from the top and draw from the bottom, convection will assist, too.
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Old 02-06-2016, 18:50   #12
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Re: Suitable relay for larger Condensor fan

I use a digital thermostat that switches up to 10amps to run a computer fan.... It's not connected to the Danfoss at all. The cabinet's temp is set at 85 degrees, and as soon as it hits that, the fan starts running and cools that area.

We also use the same digital thermostat for a fan in the spill-over fridge (so it's easy to keep spares aboard). You can get them on Amazon for $15.


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Old 02-06-2016, 19:25   #13
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Re: Suitable relay for larger Condensor fan

Quote:
Originally Posted by funjohnson View Post
I use a digital thermostat that switches up to 10amps to run a computer fan.... It's not connected to the Danfoss at all. The cabinet's temp is set at 85 degrees, and as soon as it hits that, the fan starts running and cools that area.

We also use the same digital thermostat for a fan in the spill-over fridge (so it's easy to keep spares aboard). You can get them on Amazon for $15.


Matt
Bingo...I think Matt went about this the best way.
Why spend the extra Amps when the space it not too warm?
This way the fan only runs when it "needs to" and then you can use a large enough fan to actually make a difference and move some serious air out of the locker!

Another advantage is that it is totally independent from frying your controller and putting your refrigerator/freezer out of commission mid cruise, anther Big Plus.
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Old 03-06-2016, 13:43   #14
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Re: Suitable relay for larger Condensor fan

I have a keel cooled Vitrifigo. No fan, but when I'm really putting it to work freezing one of these things:

Amazon.com : Arctic Ice Tundra Series Reusable Cooler Pack, 5-Pound : Sports & Outdoors

for our Aerogel insulated freezer bag (one of two which we swap daily)
the compressor gets quite warm. I installed a 130 degree snap disc switch on top of the compressor to ventilate its compartment.

We also use a couple of these:

http://www.amazon.com/Arctic-Ice-Ala...7PYE33TYBHFSJC

for the insulated veggie bag. Same scenario as the freezer blocks.
If your freezer can attain a low enough temperature (zero f.), the first one really works great.
The second one doesn't need to go much below 32f. to work for a veggie bag.
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Old 03-06-2016, 18:41   #15
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Re: Suitable relay for larger Condensor fan

My unfortunate install location puts the condenser in the top of a cockpit locker that shares air with the engine. I know, not ideal, but it's what I've got.
So the snap thermostats won't work for me. I'll be using a small relay to run an additional fan to pull cooler air from the cabin and duct it over the condenser.

If/when this reefer dies, I'll be relocating the condenser to a better place, but for now I'm using what the PO left me with.


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