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Old 12-29-2012, 10:19 PM   #1
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Default Trying to select a relay for my fermentation temperature contrroller.

Howdy, folks,

My objective is to add a heating function to my Mother of Fermentation chiller. The chiller was great in the summer, but now I need heat!

As suggested by another board member, I am going to use a reptile heater for this purpose. This type of heater is a 60W unit that plugs into a standard lightbulb socket. I aim to use the same thermostat that I already have, the Ritetemp unit that has been popular in the past. I am currently using this, in the typical setup, to power a 12VDC fan, with an AC adapter rated at 0.5 Amps. I looked at the relays at the Rat Shack briefly. I'm not sure whether the voltage and the ratings listed for the relays are for the relay's power source, the AC adapter, or for the the demands of the heating element.

Any guidance would be appreciated,

Todd

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Old 01-03-2013, 02:34 AM   #2
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Bump.

I'm looking for similar information - just picked up a BCS-460 and need to figure out what relays to use with fermwraps and a 7cf GE freezer. It looks like a 15-20 amp SSR is sufficient for the freezer. However, it looks like the fermwraps draw about .5 amps, (40 W at 115v). Since there don't seem to be many 1 amp relays out there, the relay would be of dubious value, and i'm concerned that it'll blow under a power spike, i'm wondering if i can get away with a standard 20 amp 110/115v AC relay.

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Old 01-03-2013, 03:06 AM   #3
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You need a analog relay as opposed to an ssr

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Old 01-03-2013, 11:41 AM   #4
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If you are going to control both heating and cooling with a BCS-460 you should probably use SSR's for each. The current rating of the SSR does not have to match the rating of the load, but it must be as large or larger. Personally, I have standardized on using only 40A SSR's, as that way I only have to have 1 or 2 as backups for any application. The increased cost is minimal.

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Old 01-03-2013, 04:24 PM   #5
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Originally Posted by brewguyver View Post
Bump.

I'm looking for similar information - just picked up a BCS-460 and need to figure out what relays to use with fermwraps and a 7cf GE freezer. It looks like a 15-20 amp SSR is sufficient for the freezer. However, it looks like the fermwraps draw about .5 amps, (40 W at 115v). Since there don't seem to be many 1 amp relays out there, the relay would be of dubious value, and i'm concerned that it'll blow under a power spike, i'm wondering if i can get away with a standard 20 amp 110/115v AC relay.
A 20A relay will work, as long as the amp rating is greater then the device you are switching you are fine. If you have a 12vdc power supply already then get one that switches with 12vdc.
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Old 01-03-2013, 04:56 PM   #6
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Originally Posted by Monster Mash

A 20A relay will work, as long as the amp rating is greater then the device you are switching you are fine. If you have a 12vdc power supply already then get one that switches with 12vdc.
You'd recommend using a 12v dc power supply rather then directly using the BCS's 5v outputs to control the relays?
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Old 01-03-2013, 05:51 PM   #7
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Since you have a BCS-460 which uses a 5v supply, stick with relays that work on 5 volt. Also, whether electro-mechanical or solid state, make certain that the total low voltage current required is less than that available from the power supply.

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Old 01-03-2013, 10:57 PM   #8
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Thanks to everyone for your help so far!

It looks like I've got some flexibility with the amperage of the relays and I could standardize (e.g. 20A, 25A or 40A). I'm planning on connecting this to a dedicated 20 amp circuit with a GFI enabled breaker (to protect against condensation or blow-off shorting the system).

As far as relay type goes, should I be using a random turn-on relay for the freezer and zero-voltage turn on for the heaters (resistive loads)?

Also, any thoughts on using fuses between the outlet and the SSRs? Originally I wasn't going to wire them in, but it looks like a lot of diagrams in the eBrewing section have dedicated fast-blow fuses wired in. Some also have heat-sensitive fuses as a back-up.

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Old 01-03-2013, 11:45 PM   #9
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Quote:
Originally Posted by brewguyver View Post
Thanks to everyone for your help so far!

It looks like I've got some flexibility with the amperage of the relays and I could standardize (e.g. 20A, 25A or 40A). I'm planning on connecting this to a dedicated 20 amp circuit with a GFI enabled breaker (to protect against condensation or blow-off shorting the system).

As far as relay type goes, should I be using a random turn-on relay for the freezer and zero-voltage turn on for the heaters (resistive loads)?

Also, any thoughts on using fuses between the outlet and the SSRs? Originally I wasn't going to wire them in, but it looks like a lot of diagrams in the eBrewing section have dedicated fast-blow fuses wired in. Some also have heat-sensitive fuses as a back-up.
You may be trying to over engineer this. At most I would put a 1 amp fuse in the line to the BCS power supply. The normal 20 amp circuit breaker will be all that is necessary for the freezer and heating element. I would think that a zero crossing SSR isn't required for a resistive load. I'm not sure that it is even required for an inductive load, only for delicate electronic applications.

I'm not certain if a GFCI outlet is a good idea for a freezer. The instructions that came with my freezer said to not use a GFCI protected outlet, but that may be only to reduce the possibility of the freezer not running.
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Old 01-04-2013, 12:59 AM   #10
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Quote:
Originally Posted by ChuckO View Post
You may be trying to over engineer this. At most I would put a 1 amp fuse in the line to the BCS power supply. The normal 20 amp circuit breaker will be all that is necessary for the freezer and heating element. I would think that a zero crossing SSR isn't required for a resistive load. I'm not sure that it is even required for an inductive load, only for delicate electronic applications.

I'm not certain if a GFCI outlet is a good idea for a freezer. The instructions that came with my freezer said to not use a GFCI protected outlet, but that may be only to reduce the possibility of the freezer not running.
Good point on the GFCI. I have a plug-in one that I use with my pumps on brew day - I could use that with the heaters instead of having a GFCI for the whole circuit. That way the fridge is covered and I have extra protection where a short is likely to occur.

My brewing partner is an electric/product engineer - he wants to make extra sure I don't burn down the house. There are handful of different parts that he's concerned about, including using quencharc capacitors to reduce switching noise on the relays, use of random turn-on relays to protect the freezer compressor, and a few special fuses as fail-safes, etc. That stuff is over my head.

My goal is to follow the KISS approach as much as possible, but make sure there's a little CYA in there as well. My initial thought was just to wire in the 4 appropriate relays along with the BCS, and then have the right wiring and fuses at the breaker to protect against surges and shorts.
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