Board logo

Alternator exciter wire without lamp
Mudchute - 14/7/18 at 01:07 PM

Hi guys,

My Acewell 7659 dash uses its own power wire to monitor voltage levels and will bring on the battery light at whatever programmed voltage I input. Subsequently I don't need a lamp in my alternators exciter wire.

Can anyone help me determine what resistors/diodes/if any I will need in this wire for my mx5 alternator in my Haynes please?


This is my 2nd to last electrical hurdle to jump before I can call the loom done and fire it up!

[Edited on 14/7/18 by Mudchute]

[Edited on 14/7/18 by Mudchute]

MikeR - 14/7/18 at 01:44 PM

Could you measure the resistance of the bulb then get a resistor of the same value that can handle the wattage the light outputs?

Mudchute - 14/7/18 at 01:46 PM

I have no bulb. I've not used any of the MX5's loom or engine management and instead used my own.

theconrodkid - 14/7/18 at 01:50 PM

i seem to remember you do need some sort of a resistance in the ind lead so either a bulb, hidden or otherwise or a resistor, i would go for simple and have a bulb as in the original, i also wired a LED into the oil pressure gauge on my MK1 MX5 (the best car ever built) as its,s nice to see when a problem is occuring
if it,s a MK2, the alternators are different and i think have an external regulator

SteveWalker - 14/7/18 at 02:13 PM

Just a thought. The resistance of a normal bulb increases around 15-fold from cold to white-hot in a fraction of a second. A resistor will vary little. I don't know whether this would have any effect on an alternator and the choice of resistance.

Mudchute - 14/7/18 at 02:25 PM

Whilst looking for a wiring diagram for my MX5's alternator (unsuccessfully) I began looking up 3 wire alternator wiring and multiple looms had some form of diode or resistor in them hence the question. If anyone can say with any certainty I don't need any form of resistor/diode then I'll wire it straight up.

Its a mk1 alternator not the ecu controlled mk2.

theconrodkid - 14/7/18 at 03:15 PM

as i said above, pretty sure you do need one, i seem to remember people putting all LED bulbs in their dash and it not charging till they put the correct bulb in the circuit, might as well stick one in now than find it dont work and do it again later.

adithorp - 14/7/18 at 03:50 PM

Quick mental calc' days somewhere around 50ohm resistor would do. Alternative would be hide s bulb holder away somewhere.

gremlin1234 - 14/7/18 at 05:00 PM

quote:
Originally posted by adithorp
Quick mental calc' days somewhere around 50ohm resistor would do. Alternative would be hide s bulb holder away somewhere.

yep 50 ohm is about right
2.4W at 12V is 200mA, which is about 60ohm
so a 50 or 60 ohm resister at 3W would do.

as adi says... just hide a bulb under the bonnet or dash

MikeR - 14/7/18 at 08:16 PM

Why hide it? Could be useful to have a light near the engine if you have a problem at night ?

starterman - 15/7/18 at 02:51 PM

Why not have a self-exciting alternator?

gremlin1234 - 15/7/18 at 04:36 PM

quote:
Originally posted by starterman
Why not have a self-exciting alternator?
I guess because he already has the one from the doner car.
but certainly an option

Mudchute - 15/7/18 at 10:50 PM

I don't want a light hidden or otherwise as that'll mess with my OCD and I'm definitely not buying another alternator as I have a working one fitted already I just need to wire it up correctly.

Thanks for the suggestion on resistor. One further question on that, the diagrams I've seen for people with similar scenarios had a bulb, resistor and diode, do I need the same?

gremlin1234 - 15/7/18 at 11:49 PM

quote:
Originally posted by Mudchute
I don't want a light hidden or otherwise as that'll mess with my OCD and I'm definitely not buying another alternator as I have a working one fitted already I just need to wire it up correctly.

Thanks for the suggestion on resistor. One further question on that, the diagrams I've seen for people with similar scenarios had a bulb, resistor and diode, do I need the same?
the light is just a high power resistor. show us the diagrams, but I doubt you would want extra diodes etc
ps for ocd, you can know it's done right with a bulb, since that's what the original circuit required.

starterman - 16/7/18 at 06:37 PM

quote:
Originally posted by Mudchute
I don't want a light hidden or otherwise as that'll mess with my OCD and I'm definitely not buying another alternator as I have a working one fitted already I just need to wire it up correctly.

Thanks for the suggestion on resistor. One further question on that, the diagrams I've seen for people with similar scenarios had a bulb, resistor and diode, do I need the same?


I wasn't suggesting you buying another alternator. You could make your current one self-exciting.

Mudchute - 16/7/18 at 06:48 PM

quote:
Originally posted by starterman
quote:
Originally posted by Mudchute
I don't want a light hidden or otherwise as that'll mess with my OCD and I'm definitely not buying another alternator as I have a working one fitted already I just need to wire it up correctly.

Thanks for the suggestion on resistor. One further question on that, the diagrams I've seen for people with similar scenarios had a bulb, resistor and diode, do I need the same?


I wasn't suggesting you buying another alternator. You could make your current one self-exciting.


Sounds like witchcraft, how is this possible?