Hello Dave,

When applying 144 volts to a 1500 watt heaters that is design for 120 volts,

it becomes 1800 watts with the increase 24 volts over 120 volts and the

ampere remain the same. 1500/120 = 12.5 amps or 25 amps for two heaters in

parallel.

(1500w x 144v)/120v = 1800w

1800w / 144v = 12.5 amps

It would be 3600 watts at 144 volts if the heaters were in parallel. This

would be 25 amps. When we put two 1800 watts heater in series this is like

two resistors in series and the voltage drop is now 72 volts across each

heater which is like a voltage divider.

Now when a 1500 watt heater design for 120 volts has half the voltage or 60

volts for a 1500 watt or 72 volts for a 1800 watt, each heater section is

reduce to 1/2 the wattage or 900 watt per each heater.

900w / 72v = 12.5 amps

This is how electric ranges work. For high we switch 240 volts to two

parallel 240 rated elements and for medium it may switch the two elements in

series for reduce wattage.

Therefore two 1500 watt heaters rated for 120 volts that are install in

series should be 12.5 amps. In a series circuit, the ampere should be the

same, where the voltage divides across alike resistances, while in a

parallel circuit the voltage is the same, but the ampere doubles.

I would use a 15 amp fustron that is design for interrupting loads or a 20

amp Circuit breaker.

To test out your heaters in series, wire them up in series and plug them

into a receptacle and you should see the voltage be about 60 volts across

each heater.

Reduce voltage, reduces the wattage.

Roland

----- Original Message -----

From: "dave cover" <

[email protected]>

To: <

[email protected]>

Sent: Wednesday, September 26, 2007 2:10 PM

Subject: [EVDL] Ceramic heater wiring 101

> I'm wiring up my ceramic heaters and I want to make sure I understand

> how to properly size the wires and fuses. Suppose we have a 144v pack

> and I'm using two 1500 watt heating elements wired in series.

> To calculate wire size I would divide 3000 watts by 144 volts, 20.8 amps.

> Looking up wire sizes in an AWG chart (MIL-STD-975),

> #12 is rated for 25 amps. I want the fuse to protect the wire and

> components,

> so I should stay below the rating of the wire. But this is getting close

> to the normal draw for the heaters. So to add some margin I should go

> for a #10 wire and a 25 amp fuse.

>

> Is this the correct way to size things up? Since ceramic heaters

> limit current as they get hotter, wouldn't my real world draw be less

> than the 20.8 amps?

>

> Thanks for the help,

>

> Dave Cover

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