New speedhut gauges, no alternator now

[5t341tH]

Hey all. I recently installed some Speedhut gauges into my 620 and so I removed the stock cluster with the dummy lights. I disconnected the harness that plugs into the back of the cluster and I have it hanging there. I had a feeling that my alternator wouldn't charge anymore because the dash light is no longer there. What do you guys recommend I do so I can get the alternator to charge the battery again? Thanks

 

Edited November 18, 2020 by 5t341tH

[thisismatt]

You need to hook up the charge lamp. The alternator needs the power supplied through the lamp to power the field windings until it gets going, at which point it then starts putting out +12V and cancels out the potential across the lamp, making it go off.

[5t341tH]

18 minutes ago, thisismatt said:

You need to hook up the charge lamp. The alternator needs the power supplied through the lamp to power the field windings until it gets going, at which point it then starts putting out +12V and cancels out the potential across the lamp, making it go off.

That’s what I figured. But how can I trick this charge lamp now? I am running aftermarket gauges now so that charge lamp will no longer be available 

[Draker]

Hook it up to 12v switched power

[thisismatt]

Why do you not want a charge lamp? KOEO it lights to show you have power, KOER it goes out to show you everything is working, or it glows dim or comes on fully to show you the alternator is failing/failed.

Edited November 18, 2020 by thisismatt

[datzenmike]

A 8* watt bulb draws about .6  amps so it's resistance is 18 ohms. Replace the bulb with an 18 ohm resister rated at 8 watts. The wattage is important as this is how much heat it must dissipate just like the dash light it is replacing. 

 

I would find a way to mount a red lens and charge bulb in the dash somehow/somewhere. It's only on at start or if something goes wrong with the charging system. The rest of the time it's invisible.

 

*I think the brightest bulbs like the signals and charge lights are 8 watts but is significantly different I don't think it will matter to the alternator.

 

 

Icehouse.... do you still have that ohm's Law tattoo???

[thisismatt]

You're right, I take my previous comment back. You shouldn't hook it straight to switched ignition because it is essentially a ground (why the light comes on before alt is operating).

[5t341tH]

Yea I will probably just wire up a bulb to bridge the 12v and alt light on the harness. I would assume an led bulb wouldn’t provide the same affect I need?

[thisismatt]

I think it can be done, but I don't know the specifics.  It may also not warn you correctly if the alt is trying to, essentially, illuminate the bulb in reverse.

[datzenmike]

Probably not, here's why. Both ends of the bulb have to have 12v on each end to be off. If the alternator is not charging power flows from the battery through the bulb (lighting it) to the alternator. If for some reason the alternator should begin over charging, current would flow from the alternator through the bulb (lighting it) to the battery. LEDs are diodes, they only flow in one direction and also the current may be so low that it won't 'excite' the alternator to 'get the ball rolling' on the charge.

[thisismatt]

Right, I'm just not sure that's the correct failure mode from the alternator.

[5t341tH]

I just tested by question with an led bulb. I bridged 12v from the harness plug and the alternator light with an led bulb. Looks like the bulb comes on with ACC and turns off once engine is started. Alternator does kick in and charge to 14.5v. I removed the LED bulb and started the engine and alternator does not come on and voltage stays at 12.7v

[datzenmike]

NO and ACCY ....Yup because I was looking at a 720 wire diagram. Well that's good to know about the LED.

[5t341tH]

Thank you both for your inputs. I think I have it figured out