Ski Builders Forum

I got my controller built, limped along with some wiring diagrams and pictures and managed to get it wired up right the first time. I was pretty stoked to see it working without getting zapped or breaking anything expensive. I've done some research on this stuff, but haven't gotten straight answers or read over some things. Sorry if there is any repetition and I hope some one gets some value out of this.

Here are the questions so you know before you read on:
1. Do need a 220v50A power cord or would a lower rated cord work?
2. What wattage can I go up to on heat blankets?

But I really don't know enough about wiring it up to what I have available at the shop. What I know is that we have 3 phase available, Wired for 220v with a 50 amp outlet for a welder. I assume the fact that I have 3 phase available won't be much of a factor. My questions are more toward the 50 amp outlet.

I built my controller with a standard 3 wire cable I bought from the local hardware store. I believe it is actually rated for 120v. I connected it to a 220v, 20 amp outlet because I could test it out with my air conditioner socket. Everything worked perfect.

Now I've learned that the cable I bought isn't rated for the 220v I'm using, and much less than the 50 amp plug I may have to use. So my question is, will hell break loose if I put the 220v,50a plug on the lower rated power cord? I'm also assuming a 50amp outlet will not cause any harm to my controller or blankets, correct? Basically I'm trying to save some cash here and not buy an EXPENSIVE cord for a 50 amp outlet. I'm not wired up for any other 20 or 30 amp service. Any suggestions?

The next question is related. before I go into it, I am running a controller based on happy monkey with 2 pids and 2 SSRs. With the general rule that I've heard on heat blankets to have 2 to 3 watts per square in this would leave 14"x80"=1120 *2 or *3 would give me 2240 and 3360 watts respectively for 2-3w target . I calculate that I will need 10.1818 amps for 2w/in 15.27 amps for the 3w/in. I'm not totally sure what happens to amperage when I have the contactor switch splitting into 2 25A SSRs, then into 2 heat blankets. Basically does having 2 blankets pulling 15 amps each burn out the 25 amp contractor switch? Would something more like 2600 watt pair of blankets work better because they are each pulling 12 amps (12*2 is less than the 25A available)?

Thanks for the help everyone!

pretty sure you won't be able to use 3 phase power with the PID and heat blankets. They will have been designed for single phase 110/120 or 220/240V. Not entirely sure though. I think also that's why noone has replied to this thread. Electricity is the one thing is this dangerous hobby that should be at least checked by someone who absolutley knows what they are talking about. Not trying to be a narc.

Thanks for some input.

I'm really just concerned on using that lower rated power cord. There are others that have talked about what blankets to use, so I can go on what they have used.

I think DBS might know a thing or 2 on this?

As far as what I've read, 3 phase has 3 120v lines coming in, but somehow is not a series and somehow works out to be something like 208V. No idea why it is used.

prospectsnow wrote:I got my controller built, limped along with some wiring diagrams and pictures and managed to get it wired up right the first time. I was pretty stoked to see it working without getting zapped or breaking anything expensive. I've done some research on this stuff, but haven't gotten straight answers or read over some things. Sorry if there is any repetition and I hope some one gets some value out of this.

Here are the questions so you know before you read on:
1. Do need a 220v50A power cord or would a lower rated cord work?
2. What wattage can I go up to on heat blankets?

But I really don't know enough about wiring it up to what I have available at the shop. What I know is that we have 3 phase available, Wired for 220v with a 50 amp outlet for a welder. I assume the fact that I have 3 phase available won't be much of a factor. My questions are more toward the 50 amp outlet.

I built my controller with a standard 3 wire cable I bought from the local hardware store. I believe it is actually rated for 120v. I connected it to a 220v, 20 amp outlet because I could test it out with my air conditioner socket. Everything worked perfect.

Now I've learned that the cable I bought isn't rated for the 220v I'm using, and much less than the 50 amp plug I may have to use. So my question is, will hell break loose if I put the 220v,50a plug on the lower rated power cord? I'm also assuming a 50amp outlet will not cause any harm to my controller or blankets, correct? Basically I'm trying to save some cash here and not buy an EXPENSIVE cord for a 50 amp outlet. I'm not wired up for any other 20 or 30 amp service. Any suggestions?

The next question is related. before I go into it, I am running a controller based on happy monkey with 2 pids and 2 SSRs. With the general rule that I've heard on heat blankets to have 2 to 3 watts per square in this would leave 14"x80"=1120 *2 or *3 would give me 2240 and 3360 watts respectively for 2-3w target . I calculate that I will need 10.1818 amps for 2w/in 15.27 amps for the 3w/in. I'm not totally sure what happens to amperage when I have the contactor switch splitting into 2 25A SSRs, then into 2 heat blankets. Basically does having 2 blankets pulling 15 amps each burn out the 25 amp contractor switch? Would something more like 2600 watt pair of blankets work better because they are each pulling 12 amps (12*2 is less than the 25A available)?

Thanks for the help everyone!

First thing first there is no difference between a 110v wire and a 220v wire. All wire used for 110 or 220 is rated for 600v. The only thing is you're using the white wire as a hot. This wire should have red tape applied to both ends indicating that it is a hot wire.

Now, you didn't say what gauge wire that is or how long of a distance it's ran though, and that's where you may have an issue. For a 30amp circuit you should run at least 10 gauge.

If each blanket is pulling 15 amps and wired to an individual ssr then that ssr has a 15 amp load on it. If both loads are coming through the same contact on a 25 amp rated switch, then yes you are overloading the switch.

You really may want to replace the 50amp breaker with a 30amp breaker, replace the 50amp outlet with a 30amp outlet, and stick with 2600 watt blankets.

prospectsnow wrote:As far as what I've read, 3 phase has 3 120v lines coming in, but somehow is not a series and somehow works out to be something like 208V. No idea why it is used.

3-phase is used for power distribution because there's less transmission loss. When you have 3-phase to the premises, it's usually then split down to single phase(s), but in some cases, like yours, you have 3-phase available. that's a good thing if you want to run heavier machinery.

There's 2 types of 3-phase supply. 3-wire supply gives you 3 hot wires, each 120° out of phase with the next, 4-wire supply gives you 3 hot + neutral.

Getting a single phase from a 4-wire supply is easy - you connect your single phase load between one hot wire and neutral. With 3 phases at a nominal 120V, that gets you the possibility of 3 totally separated 120V supplies.

From a 3 wire supply, it gets a bit more complex. Timply connecting phase to phase (again assuming 120V) gets you 208V. The dded, you say? Indeed. But it's explained by this phase diagram -



At any point, you have at most 208V between any 2 given phases. 208V is 120 * sqrt(3), not that this helps you.

Where 3-phase is really useful is in running big motors (woodworking machines, for example), where a 3-phase motor gives you a lot more clout. 3-phase machines can be "converted" to single phase operation, but, as can be expected, you lose a lot of power and efficiency.

I concur with DBS. Get a sparky to run you a supply capable of supplying the amount of current you want to use, with breakers at the right ratings. Overloading your breakers is risking this: