Electrical: What size of fuse/circuit breaker?

[junior]

So finally after many, many years of not having a heater, I got around to hooking up my heater blower motor. Now I need to know what size of fuse or circuit breaker to use since the motor is now 12v instead of the original 6v one. The topic of fuse sizes versus 6v to 12v conversions is not covered in Randy Rundel's Guide. Would I measure the total amount resistance in the heater circuit with the heater switch in the 'high' position and the circuit dead, and then divide that into 12volts (E=IR)? Regards, Junior.

[brngarage]

If you are using a 12 volt heater blower motor from a later Studebaker, I'd just find out what fuse rating that later Studebaker used.

[junior]

If you are using a 12 volt heater blower motor from a later Studebaker, I'd just find out what fuse rating that later Studebaker used.

Do you know what that would be? Thanks. The motor I used was a generic one from NAPA, and was not supplied with any data such as maximum current draw. The question I posed is specific to me for the heater blower motor, but also what does one do for all the circuits when converting from 6 to 12 Volts? I never considered that before, until now, and have never had an issue with the circuit breakers/fuses before. When converting from 6 to 12v, the approx. current draw with all things considered should be about 1/2 of what is with the original 6 volt system...does that mean changing all original circuit breakers/fuses to half their original values to protect the component, not just the conductor wires.? Thanks, Junior.

[52hawk]

How about asking NAPA if they can recommend fuse size? All I can say is a modern car would have a 25 or 30 amp fuse on the heater. If you have your heater in the original mounting 'can' would you give me the NAPA part# ?? I need to get one for my '61.

[brngarage]

Junior:
I think you are "generally" correct. Since doubling the voltage reduces the amp draw by 1/2, using fuses of 1/2 the 6 volt requirement should be correct. I will try to contact Randy Rundle tomorrow and see what he has to say and if he would like to update his 6 volt to 12 volt conversion book with some discussion of this subject. Since the amp draw is 1/2, the existing wiring (if it is in good condition) should be MORE than adequate as it handled the original amps load.

Thanks

[junior]

If you have your heater in the original mounting 'can' would you give me the NAPA part# ?? I need to get one for my '61.

made a mistake, did not get my motor from napa, but a local place called Greggs. regardless, if you do a search on the forum you`ll come across a thread where a guy did use a generic napa motor which worked as I recall with no modifications. even if I did buy it from napa, the canadian part number would do you no good, as napa uses a completely different numbering system from american napa, go figure. anyways, the motor I purchased was a Siemans PM325 for about 50$ 3 years ago. I think I had to cut the mounting studs a little shorter to fit in the stude housing, and no modifications to the squirrel cage, but I as I said, that was 3 years ago, and only installed it in the car this summer, works like a charm! Regards...Junior

[junior]

Junior:
I think you are "generally" correct. Since doubling the voltage reduces the amp draw by 1/2, using fuses of 1/2 the 6 volt requirement should be correct. I will try to contact Randy Rundle tomorrow and see what he has to say and if he would like to update his 6 volt to 12 volt conversion book with some discussion of this subject. Since the amp draw is 1/2, the existing wiring (if it is in good condition) should be MORE than adequate as it handled the original amps load.

Thanks

Be interested in what Randy has to say...I did some research on the net today and am now somewhat confused. Regards, Junior.

[brngarage]

Junior:
I just spoke with Randy Rundle of Fifth Avenue and he confirmed that using a fuse of half the amperage required for a 6 volt system would be correct for a 12 volt system.

[junior]

Junior:
I just spoke with Randy Rundle of Fifth Avenue and he confirmed that using a fuse of half the amperage required for a 6 volt system would be correct for a 12 volt system.

Howard, thanks for checking into this...will swap the 20 amp breaker with a 10 amp. Hope this helps others out with 6 to 12V conversions. Regards, Junior

[studebakerkid]

Which generic one from NAPA.....some of those later heater motors had a tube running from the motor housing to the fan and actually used part of the air flow to cool the motor and without the tube the motor will burn out faster.

[johnod]

A fuse is to protect the wire. The fuse you use should be rated no more than the max rated ampacity for the wire size. There are charts on the net.

Starting to look like winter here Junior hows things your way?

[junior]

A fuse is to protect the wire. The fuse you use should be rated no more than the max rated ampacity for the wire size. There are charts on the net.

Starting to look like winter here Junior hows things your way?

ya, thats what I discovered, and why I am confused...what about the components, say radio, tach etc, aren`t fuses for these to protect the component, not the circuit wires? We've already had some snow, winter is indeed coming. Still taking the Stude out as much as possible, coldest it's been is -7C (so far), sure is nice to have a heater after all these years. My goal is to drive the car until my birthday (mid nov.), some years I make it, some years I don't. How about you guys....did ya see all the snow Winterpeg got last week? Regards, Junior.

[brian6373]

Since motors by far are much higher amp draw, I don't think radios and tachs should be very high in comparison. As was posted earlier your wiring, if in good condition, is way more than anything you'll need for 12V loads. Are those components original 6V with resistors. or later 12V?
Brian

[johnod]

ya, thats what I discovered, and why I am confused...what about the components, say radio, tach etc, aren`t fuses for these to protect the component, not the circuit wires? We've already had some snow, winter is indeed coming. Still taking the Stude out as much as possible, coldest it's been is -7C (so far), sure is nice to have a heater after all these years. My goal is to drive the car until my birthday (mid nov.), some years I make it, some years I don't. How about you guys....did ya see all the snow Winterpeg got last week? Regards, Junior.

When thing are done properly, the wire is sized for the power requirements of the whatever, lets say radio.

The radio draws a certain number of amps, so you use the wire size that has a current carrying capacity closest to that number.
If the amps required for the radio fall between the ampacity/current carrying capacity, of two wire sizes you round to the larger size.
If the radio suddenly starts drawing a lot more amps there is a problem, and the wire will start to over heat etc,
This is when the fuse is supposed to blow if everything works properly, thus protecting the wire.

Given that all the pieces in a circuit remain the same except the voltage, then your wire is probably twice the size you require.

If your interested

Here is your power formula with a simple explanation of how it works.

http://www.cdxetextbook.com/electrical/princ/fund/solvepowereq.html

That along with Ohms law are very handy tools around anything electrical, be it house or auto.


There is another theory , Wires are actually small tubes, the copper is there only to give support to the tubes.
Electrical smoke travels throught the tubes to wherever you need it.
If there is a problem and the smoke escapes, the electrics don't work.
This is most easily visable in anything that has Lucas printed on it somewhere.

http://www.google.com/imgres?hl=en&sa=X&rls=ig&tbm=isch&prmd=imvns&tbnid=gNOjegDIvTufWM:&imgrefurl=http://jalopnik.com/399791/joe-lucas-prince-of-darkness-british-electrical-system-jokes&docid=Le3yRpmTo0vkcM&imgurl=http://cache.jalopnik.com/assets/images/12/2008/08/medium_Lucas-Electrical-System-Jokes.jpg&w=478&h=358&ei=yQh7UNjWLJKFyQGDp4DYBg&zoom=1&biw=1920&bih=899&iact=rc&dur=219&sig=111293245084626629019&page=1&tbnh=125&tbnw=163&start=0&ndsp=51&ved=1t:429,r:11,s:0,i:109&tx=85&ty=72

[junior]

. Are those components original 6V with resistors. or later 12V?
Brian

a mixture of both...can`t remember offhand which is which right now, but all really voltage sensitive components such as the gauges, are 12v, or have runtz converters. there is one of those really big ceramic based resistors under my dash, but as I recall, only the wiper motor is connected to that. all bulbs, fuel pump, radiator fan, and heater fan are all 12v. regards, junior.