# How to determine heater size...

#### catman81056

Joined Apr 7, 2012
12
I'm rewiring my lathe motor from the original 440 3ph to 208/220 3ph. The motor is rated at 5hp. I'm using a 10 hp 3ph motor to make my RPC. I'll post a few pics of the electrical panel and voltage application plaque. I've been told the when I convert to the 208/220 I'll need to change the heaters. Thats where I get lost. I'm sure I can switch the motor wires via the tag diagram but how can i figure what heaters to get?
Any help would be greatly appreciated.

#### gerty

Joined Aug 30, 2007
1,276
Typically what happens is when you cut the applied voltage in half, you double the required current. Since you're going from 440 to 240 that's what's happening.

edit: A quick look at your motors data tag will tell you what the current will be at both voltages, and if you do themath you'll see what I mean.

#### catman81056

Joined Apr 7, 2012
12
So you figure what heater you need by the current you will use? Are the heaters rated by current used? Not meaning to sound nieve here, but I don't know squat about heaters or how the pick them. And thanks for the reply.

Just went out and checked the tag. By current do you mean amps? I see on the tag low voltage amps are 17.5 and high voltage amps are 8.8. So would you get heaters rated for 17.5 amps?
The tag also says voltage 220/440. I've measure the legs coming from my RPC and they are L1-L2 203, L1 L3 203, L2 L3 246. Would this run the motor?

Last edited:

#### mcgyvr

Joined Oct 15, 2009
5,394
heaters in a lathe???
anti-condensation heater or something?

#### catman81056

Joined Apr 7, 2012
12
Thanks for the link. I have to say that looking at the pic of the control box on my lathe I'm pretty sure where the 3 circuit breakers are, but where are the heaters located?

#### strantor

Joined Oct 3, 2010
5,226
Thanks for the link. I have to say that looking at the pic of the control box on my lathe I'm pretty sure where the 3 circuit breakers are, but where are the heaters located?
That's hard to say. They are usually built into the main starter contactor, or a separate block from the starter contactor. I think the 2 components in the bottom left are a mechanically interlocked reversing contactor? So I would assume that the component to right of that is your starter contactor, so I would look there. Google motor starter heaters so you know what you're looking for. If you still can't find it, post a pic that is more straight-on, or from a downward perspective, looking up into the panel, that would help me identify it more easily.

EDIT: to make sure you get the right heaters, check the model & rev # on the contactors. There are different heaters for different models of contactor, they do not work across all platforms. If you contact your local GE electrical supplier, they should be able to help you select the correct heater.

#### gerty

Joined Aug 30, 2007
1,276
heaters in a lathe???
anti-condensation heater or something?
A lot of machinery uses thermal protection. The way a heater works is to be in series between the contactor and moter. One for each phase. When the motor current gets higher than the "heater" is rated for, it actually heats up and trips a lever in the overload unit.
That in turn opens a set of contacts, usually wired into the neutral side of the motor contactor coil. Shutting off the coil voltage keeps the motor from further damage. Heaters, unlike fuses, are normally not interchangable between manufacturers.

http://www.southlandelectrical.com/itemdesc.asp?ic=W59-NS

edit Strantor beat me by 2 min

#### catman81056

Joined Apr 7, 2012
12
Dug alittle deeper and took more pics. I found the hearter elements, 4 altogether, 2 different kinds. The 2 contactors on the bottom left have a tag stamped; CR109 CT or CI, the second letter is faint. The heater elements are marked 81D 551. The single contactor on the right is tagged with CR106BO, with elements CO36A. Here are a few pics:

What do these do?

#### strantor

Joined Oct 3, 2010
5,226
yep those are your heaters. If you take them to your electrical supplier, they should be able to help you find properly rated replacements.

Those that you asked about in the last pic are (the 4 in the bottome left) probably control relays for whatever functions the lathe has. The thing in the top right is a 200VA control voltage transformer. This transformer is probably also going to give you problems because now it's only going to be outputting half the voltage that the relay coils need. Normally it would step down 480 to 240 for the relays. However, the relays have 110V coils so I assume it is center tapped. Now you have 240 coming into the panel, so I figure your relays will only be getting 55V. This information I am providing about the transformer is a best guess; if you had a schematic I could tell you with more certainty.

#### catman81056

Joined Apr 7, 2012
12
When I got the lathe I didn't get any kind of paperwork with it. I just recently ordered an owners manual and blueprint/electrical schematics from Tony Griffiths at lathes.uk. Theres no guarantee that they cover my year of lathe, hopefully they do.
I took all the info off of the transformer.
GE mod#9T51Y1430,
primary 240/480
sec 120/240
kva .200
cy 50/60
60* c rist
This lathe has a motor that controls the spindle speed that runs on 220 1ph. I could probably wire the control motor for 120v.

#### GetDeviceInfo

Joined Jun 7, 2009
1,702
I'd start by checking that your motors are dual voltage. When you look for heaters, make sure you compensate for 208vac. Your main inline fuses and transformer fuses will also require replacement, as likely will all of your power wiring. And even though your contactors will be HP rated, make sure you check that your not exceeding thier amperage rating.

Last edited:

#### catman81056

Joined Apr 7, 2012
12
Tha main motor is 220/440 3ph, the speed control motor is 220 1ph only. I'm sorta stumped on what to do about that. The electrical drawing I got today don't look anything like my lathe. Probably an earlier model.

#### catman81056

Joined Apr 7, 2012
12
Well, I found a decent buy on a transformer thats 480 primary, 208/120 secondary. The tech department at Acme said to reverse wire and use the 456 tap. The killer is its 420 miles away. Figures around $225.00 in gas which is still cheap for a total of$354.00. We'll see what happens.

#### strantor

Joined Oct 3, 2010
5,226
ok, so you're going to step up the 220 to 456 and leave all the wiring as-is? Are you sure about the amp rating on the transformer? is it going to be big enough?

#### shortbus

Joined Sep 30, 2009
7,611
You guys are making this harder than it needs to be, unless I'm missing something going on in PM's.

You have a lathe motor that is capable of running on 220/240 three phase. You have a phase converter (RPC). You have a speed changer motor that runs on 220 single phase. You have 220 to feed the RPC. Am I correct so far? then you do the following;

1) you wire the RPC to the 220 single phase.

2) you wire the RPC to the spindle motor controls and change the spindle motor to run on the 220 from the RPC.

3) you take the 220 single phase from the RPC input and wire it to the speed change controls and motor.

4) you take 110 single phase from the RPC input for any 100 single phase controls. If needed.

5) you change the heaters on the contactors as needed to match the new 220 voltage rating of the spindle motor.

6) you sit back and have a beer.