Coil box amperage ?

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
Modeltmike
Posts: 179
Joined: Sat Mar 09, 2019 5:12 am
First Name: Mike
Last Name: Sleep
* REQUIRED* Type and Year of Model Ts owned: I have 22, 24, 26 coupe, 25 pickup, 23 roadster, 27 touring and 26 Fordson.
Location: Kansas

Coil box amperage ?

Post by Modeltmike » Wed Nov 08, 2023 5:27 am

How many amps does a coil box draw. It is my understanding that a single coil should be set at 1.5 amps. Is it as simple as 1.5 x 4 = 6 amps?


Jerry VanOoteghem
Posts: 4082
Joined: Sun Jan 06, 2019 4:06 pm
First Name: Jerry
Last Name: Van
Location: S.E. Michigan

Re: Coil box amperage ?

Post by Jerry VanOoteghem » Wed Nov 08, 2023 6:23 am

Modeltmike wrote:
Wed Nov 08, 2023 5:27 am
How many amps does a coil box draw. It is my understanding that a single coil should be set at 1.5 amps. Is it as simple as 1.5 x 4 = 6 amps?
Only one coil is fires at a time, so only 1.5 amps.

User avatar

Humblej
Posts: 1957
Joined: Sun Jan 06, 2019 12:23 pm
First Name: Jeff
Last Name: Humble
* REQUIRED* Type and Year of Model Ts owned: 1926 Canadian coupe, 1924 TT C-cab, 1924 runabout
Location: Charlevoix, Mi
Board Member Since: 2006

Re: Coil box amperage ?

Post by Humblej » Wed Nov 08, 2023 6:50 am

1.3 amps per coil if it is adjusted correctly.

User avatar

Mark Nunn
Posts: 1241
Joined: Mon Jan 07, 2019 8:01 am
First Name: Mark
Last Name: Nunn
* REQUIRED* Type and Year of Model Ts owned: 1926 Runabout
Location: Bennington, NE
Board Member Since: 2017

Re: Coil box amperage ?

Post by Mark Nunn » Wed Nov 08, 2023 8:06 am

Instructions for installing an E-Timer say to add a 4 amp fuse to the coil box. Total run amperage needs to be somewhere below that.


TXGOAT2
Posts: 7391
Joined: Sun Feb 14, 2021 10:08 pm
First Name: Pat
Last Name: McNallen
* REQUIRED* Type and Year of Model Ts owned: 1926-7 roadster
Location: Graham, Texas
Board Member Since: 2021

Re: Coil box amperage ?

Post by TXGOAT2 » Wed Nov 08, 2023 8:17 am

Only one coil at a time is in operation, and for some of the time during engine operation, no coil is operating. Average coil current during coil operation is in the 1.2 to 1.5 amp range. A 4 amp fuse would be correct, if a fuse is present. Coils behave differently when operating on battery current (6 volts DC) as opposed to magneto (Alternating current, about 5 volts AC to about 30 volts AC) Two coils will fire during each revolution of the engine.


Been Here Before
Posts: 654
Joined: Mon Oct 07, 2019 2:00 pm
First Name: George John
Last Name: Drobnock
* REQUIRED* Type and Year of Model Ts owned: 1922 Coupe
Location: Central Pennsylvania

Re: Coil box amperage ?

Post by Been Here Before » Wed Nov 08, 2023 9:21 am

To add to the discussion, and of course be criticized, if you observe your ampere meter, set the ignition switch to battery, and turn your motor by hand crank, with the coil buzzing, you should observe that the meter will show a discharge of about 2 amps, or one line to the left (a discharge). Of course if you use a buzz box with a three ampere meter, you will note a current draw of 1.5 to 2 amperes.
DSCN1618a.jpg
DSCN1618a.jpg (48.01 KiB) Viewed 1207 times
Scan3i1tester.jpg

User avatar

JohnH
Posts: 367
Joined: Sun Jan 06, 2019 6:57 pm
First Name: John
Last Name: Hunter
* REQUIRED* Type and Year of Model Ts owned: 1926 Geelong Tourer
Location: Blue Mountains, Australia
Board Member Since: 2002
Contact:

Re: Coil box amperage ?

Post by JohnH » Wed Nov 08, 2023 4:03 pm

The Ford ammeter installed in the dash is far from a precision instrument, and is certainly not accurate enough to set coil current using the buzz box method. It's just a rough guide that everything is working properly.
The 4A fuse specified for the E-Timer is to protect the E-Timer itself, in case a coil is completely short circuited.

Post Reply Previous topicNext topic