electrical gurus

For discussions related to designing and making ski/snowboard-building equipment, such as presses, core profilers, edge benders, etc.

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bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

electrical gurus

Post by bobbyrobie »

i seem to be having a serious problem with my heater controller. running 2 PID controllers. with 2 SSRs running 2 seperate heaters. 2 of my fuses that come directly off the switch to my block terminals keep melting down for some reason cant seem to figure out why? i obviously must be over looking something. the tc's and everything are working fine.

heres a general schematic.

Image

any ideas???
twizzstyle
Posts: 2204
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle »

How many amps are the fuses you're using?

Sounds like you're just using fuses that are too small for the current draw. These heaters pull a LOT.
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

i am using 12 amp fuses. and when i mean its melting down the actual fuse housing is melting down!
twizzstyle
Posts: 2204
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle »

How many watts are your heat blankets? Often they specify a watts per inch rating, so use that to find total wattage at full power.

Are you using 110 volts or 220?

Amps = Watts/Volts
doughboyshredder
Posts: 1354
Joined: Mon Sep 17, 2007 7:37 pm

Post by doughboyshredder »

I think your fuses are too small, or the wrong type. I don't know, I didn't use any fuses.

I am guessing 240v blankets from the wire colors on your schematic. What's your wattage rating on your blankets. 2 blankets at 2400 watts each at 240v would be drawing approximately 20 amps and could melt instead of blow a slow blow fuse. I also don't think it's necessary to have a fuse on each hot lead, but I am not 110% on fuses. Regardless you shouldn't load your fuse up anymore than 75% of it's rating, and for what I assume you are trying to protect against a fast acting fuse is best.

If you can handle real technical stuff this is a great page about fuses http://www.lnl.com/howto/fuse.htm
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

Okay, for starters, we need some more detailed information...

Your diagram shows that you are using two different wires that come off your 'breaker switch'. Is the 'breaker switch' that you describe in your diagram your 'circuit breaker' in your electrical panel, or is it your 'power switch' on your heater control box? If it's the circuit breaker in your electrical panel, then we've really got some problems to deal with. So, hopefully, it's the power switch on your control box.

You don't need to fuse two different lines in a 110 volt circuit. Only one fuse is required. Generally, it is safer to ground early on the hot lead (right after the power switch is good) so that a short that might develop anywhere within your circuit design will be protected by the fuse. I've read discussions on-line that assert that fusing the hot lead or neutral lead is equally effective, but those discussions never seem to end in agreement.

How are you getting power to the PID's? Where's your ground circuit? You absolutely must properly ground both your press frame and your aluminum pressing layers. Sharp edges, lots of pressure, and high current loads are a really potentially dangerous combination. If the sharp edge of a pressing layer should happen to cut into a heat blanket and your system isn't properly grounded, you could end up providing the run-a-way electricity a path of least resistance back to earth.

Basically, your diagrams are not complete enough for us to give you much detailed help, but I'm guessing, as stated above, that a 12 amp fuse is not near big enough to cover the current draw of two large heaters. Example: an 8 inch by 80 inch heater is 640 square inches. At 5 watts per inch, that's 3200 watts. Divide that by 110 volts and you get 29 amps per heater. Two heaters, running simultaneously, could draw as much as 60 amps... holy @*$#, did I do that right?? That's a lot of amps. I use much smaller heaters and I didn't realize how many amps the big boys could draw. This doesn't rule out that you could still have some sort of short circuit somewhere, but it certainly does seem to indicate that a 12 amp fuse is too small, regardless of what other problems might be present.

good luck,

G-man
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

thank you for the reply, sorry i should have gave you more information. i am using a smaller electrical service panel that is attached to the press and i have a 240 volt plug that is attached to it. using a 30amp relay in the box which also serves as the switch seemed like a good idea?. so its fully ground and everything. the red and black wires in the diagram are the separate 120v's coming off the breaker. the pid controllers are ground to the service panel. and are being powered from the left distribution block pictured in the diagram.

the blankets i am using are 240 volt blankets. 2400watts a piece. which works out to about 10 amps a piece.

i will get some pictures up asap
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

My earlier post was during a quick lunch break this afternoon, and after looking at this thread again, I realized that I wasn't being as attentive to some possibly important details as I could have been. I had not considered that you might be using 220/240 volts (thanks doughboy for pointing that out), but since you may well be drawing considerable amperage, 220/240 certainly has it's merits. Even so, it's difficult to be sure from your diagram if you're using 120 or 240 (I'm somewhat old school and still often refer to line voltages as 110/220), but it probably doesn't make a significant difference what voltage you're using in terms of solving your problem... you either have a short circuit, or your fusing is under-rated for the amount of current you are drawing. I'm still hoping that you are grounded correctly since you didn't mention that a circuit breaker was tripped, although it's reasonable to expect that a fast acting 12 amp fuse would blow before a 15 amp circuit breaker would trip. What size circuit breaker controls the house circuit you're using?

A question still remains, though, in that if you are in fact using 240 volts, do you need to fuse both hot lines?.. or do you need to fuse at all? To answer this, we need to ask what, in fact, are you trying to protect with the fuse. I generally use optional fuse links to protect sensitive components and wiring that may be vulnerable to damage by current levels that are below the protection capacity of the actual circuit breaker... like the PID device or some small gauge wiring in your control box. Your heater blankets draw such large amounts of current, that fusing at that level doesn't protect sensitive components that aren't rated for high current. Fusing a high current 240 volt device can actually be dangerous. As an example, I'll assume that you are, in fact, using 240 volts, and you're drawing 20 amps on a circuit that is protected by a 30 amp double pole breaker (standard 240 stuff). Let's say that you decide to install a 25 amp fuse on one of the 120 volt legs. If you were to experience a short circuit that resulted in a current draw of greater than 25 amps, the fuse would blow, but you'd still have one 120 volt leg of the 240 that would continue to energize the circuit, possibly without you realizing it. If, on the other hand, you were not to install a fuse at all, and just let the circuit breaker handle the circuit protection, the double pole breaker would de-energize both hot lines if an over-current event should occur. If you fused both hot lines, there's no guarantee that both fuses would blow and you could still be in the same boat of having a 120 volt line that was still energized. So, I say that for big current loads on 240 volt circuits, forgo the fuses and let the circuit breaker handle the over-current protection. For the same basic reasons, I don't think I'd fuse over 10 or 12 amps on a 120 volt circuit. If a fuse is blown on any device, there's always a voltage potential at one end of the fuse if the device is still plugged in or if the power switch is on. This voltage potential is always looking for a path to ground, which I have regretfully provided a f-f-f-f-few t-t-t-t-too many times. Whew. Oh, and obviously, I'm certainly no electronics guru, but I'm on quite good terms with Google.

G-man
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

Okay, the new information is helpful. Sounds like you're trying to pull 20 amps through a 12 amp fuse. Because the different 120 volt legs of the of the 240 circuit are out of phase with one another, I believe (not totally sure) that they both still pull the full amperage load during their positive phases. In other words, 20 amps each. You might still want to consider not using the fuses, and try a 20 amp breaker in the small sub-panel box that you have attached to your press. You might have to go with a 30 amp breaker because 20 amps is so close to what you are theoretically drawing, but your heaters can certainly handle 30 amps. If you were to actually check your line voltage, you might discover that you aren't actually getting the full 240 volts... I seldom do. If you're getting less than 240, it changes your circuitry math, and increases your amperage draw, putting you over 20 amps.

So, if I understand you correctly, you're running your PID's on 120 volts. Most that I've seen can go either way.

I'm curious... do the 240 volt heaters still just have 2 wires?.. or do they also include a ground wire?

Yes, pictures would be good. I'm curious about the 30 amp relay that you're using as a switch.

G-man
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

wow that was quick G-man haha. yeah i even have the blankets fused aswell. figured it wouldnt hurt. those are on 10 amp fuses i believe and they never trip. im not really sure whats going on to be honest. the last board i did i warmed it up to 120 degrees for about an hour and it worked great no problems. the top blanket sits above the alum cat track in between 2 pieces of alum. so wanted it all warm and ready to go. so i go to press and i slowly ramp it up to the 200 degree range then i notice that the temps start dropping once i get it to 200. something i just realized is that the PID controllers were still working yet the blankets weren't that seems odd since there basically feeding off the same power. the inline fuse that were melting down i believe are at least 10 gauge if not bigger. so they are much larger then the blanket wires.
so my question is if there was a short. would it not melt down when i had it up at 120 degrees?
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

ok well i just looked at it again and the power to the PIDs melted down but was still was intact enough to provide power.
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

The PID's themselves (unless they're damaged) can't draw enough current to melt the insulation on a wire, so you almost must have a short circuit close by. We need pictures of your entire system... lot's of pictures. Be sure to get one of the connections to the back of the PID's. At what point 'downstream' from your power source did your wires to the PID's cease to melt?

G-man
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

Image


Image

there are 2 wires that attach to the left ssr that come from the PID but there not attached in the bottom picture. but you can see the basic layout

none of the actual wiring melted only the plastic fuse housing.
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

Yikes. Things certainly did get hot. It's still pretty difficult to see what you have going on. It looks like there are a number of wires going to your ground bar that shouldn't be going there. I'm sure much of it is just the way the pic makes things look, and the wires may actually be going under the black plastic mounting plate. I'm thinking that there are 3 red wires that are actually connected to the ground bar, and the others that look like they are connected actually go beneath the black plate... the 2 joined red wires from the left buss bar that carry one of the 120 legs to both heaters, and the black wire from the right buss bar that carries the other 120 leg to the supply side of the right SSR. At any rate, it's a little tough to tell what's going where. One thing is pretty evident, however, and that is that you have some significant overloading problems. Even though certain wires didn't melt, in the photo, they sure look like they got pretty baked. I don't think this is just a matter of not a big enough fuse. It's probable that you have a short circuit, and it's possible that you have an improper continuity or polarity issue with the 240 volt lines. I think at this time it's best to suggest that you have an actual electrician take a close look at what you have. It looks like you're real close to having it right, and an electrician could probably zero in on the problem pretty quickly. Given what you have reported so far, it seems that you're real lucky your PID's still function properly (melted wires that supply them), and it seems prudent to not take too many more chances with them. I really don't understand why your breaker didn't trip, considering the kind of stress your control box appears to have gone through. The kind of heat effect we're seeing here doesn't happen in just an instant. It's usually more prolonged... although, it does take a bit of heat to blow a 12 amp fuse, and even more to trip a 30 amp breaker. Maybe someone else will pick up on something I'm not seeing or realizing... probably something right in front of my nose. Be sure to keep us informed of your progress and resolution.

G-man
bobbyrobie
Posts: 124
Joined: Wed Sep 17, 2008 9:17 pm

Post by bobbyrobie »

their is only 2 wires actually connected to the ground, which are the controllers ground. everything else goes under the black part 2 the other side either exiting to the heaters or to the right side SSR. it must be something i am overlooking. or their is a short some where. its really frustrating. my uncle is an electrician il see if i can get him to help me out. if the heaters were shorting shouldn't the fuses that are attached to the heater. blow first? those are the 10 amp fuses with the yellow wires pictured. i will have to go over every inch of the heaters and wiring making sure nothing is shorting out.
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