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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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Don't wire the ceramic elements in series with 144 volts. It will not help
you in any way.

If you live in an area where you need more heat, then wire them so that you
can add the extra elements as needed. These type of heaters blow more heat
with more air through them. You would be defeating this effectiveness by
reducing the overall voltage in series. There is not a problem running them
individually at 144 volts. If you need more heat just add relays or control
circuits depending on your needs. Switch in more elements in parallel if
needed.

I use a single 1500 watt heater that gets hotter than you can imagine on my
system.

Take a look at what I did with mine and email me if you need more info.

Mark Ward
95 Saab 900SE "Saabrina"
www.saabrina.blogspot.com



----- Original Message -----
From: "dave cover" <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 26, 2007 3:10 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
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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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
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev

 

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On 26 Sep 2007 at 16:32, Roland Wiench wrote:

> When applying 144 volts to a 1500 watt heaters that is design for 120 volts,
> it becomes 1800 watts ...

Remember that a ceramic heater element is not a simple resistive load. It
doesn't behave like a conventional nichrome wire heating element.

A ceramic element's resistance changes with temperature. Thus, as I
understand it, it tends to regulate its own current to maintain the design
temperature. To adjust the BTU output, all you have to do is adjust the
airflow through the element (that is, vary the fan speed).

David Roden - Akron, Ohio, USA
EVDL Administrator

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It is best to test out the heaters, to see what the ampere will be at a cold
startup. A 1500 watt heater may surge up to 18 amps during start up and
when the elements heat up, the ampere will drop.

I have a 640 watt ceramic under dash heaters, my DC-AC inverter amp meter
surges up to about 10 amps on start up and then comes back to about 6 amps.
A 1500 watt ceramic heater may surge up to about 18 amps at initial start up
while the elements are cold and should drop.

I may use a 15 amp fustron or a limitron fuse that is design to take this
overcurrent.

Lets say that the name plate ampere reads 12.5 amperes, you install a
service factor of 1.25 times the actual ampere you will read. 12.5 amps x
1.25 = 15.625 amps. A 15 amp fustron will take about 15 x 1.25 = 18.75
amps, so a this type of fuse is the proper protection for this circuit. It
will take a 15 amp circuit breaker with magnetic trips or a 20 amp thermo
trip circuit breaker.

Roland


----- Original Message -----
From: "David Roden" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Thursday, September 27, 2007 8:22 AM
Subject: Re: [EVDL] Ceramic heater wiring 101

> On 26 Sep 2007 at 16:32, Roland Wiench wrote:
>
> > When applying 144 volts to a 1500 watt heaters that is design for 120
> > volts,
> > it becomes 1800 watts ...
>
> Remember that a ceramic heater element is not a simple resistive load. It
> doesn't behave like a conventional nichrome wire heating element.
>
> A ceramic element's resistance changes with temperature. Thus, as I
> understand it, it tends to regulate its own current to maintain the design
> temperature. To adjust the BTU output, all you have to do is adjust the
> airflow through the element (that is, vary the fan speed).
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> EVDL Information: http://www.evdl.org/help/
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Note: mail sent to "evpost" or "etpost" addresses will not
> reach me. To send a private message, please obtain my
> email address from the webpage http://www.evdl.org/help/ .
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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