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 Post subject: Ammeter bounce
PostPosted: Sat Aug 12, 2017 1:35 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
Following recent replacement of my starter and alternator, my ammeter is bouncing like a wild metronome at idle. This didn't exist before the swaps. This is beyond my experience. It appears to calm down somewhat at speed. No other symptoms or complaints with any electrical systems in the Z; everything works as advertised, even the clock keeps perfect time :shock: .

Researching the problem I read similar complaints from owners of Cobras, Corvettes, Ferrari, and even aircraft. The only believable response in all of those threads indicates an overloaded diode acting as an internal voltage regulator at the (now new) alternator. (I do use a diode instead of an external regulator). That thread also mentions the needle seems to calm down at speed, but the response was that the frequency of voltage change increased so greatly at high engine speed, the ammeter needle couldn't physically keep up with it and so appeared to be steady.

Has anyone else experienced this problem and, if you did, what siZe magic wand did you hit it with to fix it?

Frank T

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1970 240Z


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 Post subject: Re: Ammeter bounce
PostPosted: Sat Aug 12, 2017 9:51 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 1181
Location: Ansonia, CT
So you no longer have the external voltage regulator? :? Hmm, you might try contacting Mike Winters. He is a wiZ on Z wiring.

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John Kish
1971 240Z - original owner


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 Post subject: Re: Ammeter bounce
PostPosted: Sun Aug 13, 2017 12:42 am 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
No I don't, but you just gave me an idea. I used to have the stock externally-regulated alternator with a standard external electro/mechanical voltage regulator box. When I upgraded to a stronger externally-regulated alternator, I deleted the external voltage regulator and installed a diode in line with the alternator instead. That of course performed the same function as the old regulator had; it only allowed current to flow one direction.

Now I have installed my 3rd alternator and I'm wondering if maybe I didn't install an internally-governed unit by mistake. If so, that would give me two diodes to flow thru instead of one. I won't be sure how that could effect my ammeter until I study a schematic and maybe take a few readings on the car, but your comment just made me think that should be considered. Thanks.

The diode was required when I earlier installed a pointless electronic ignition. If you don't use the diode, the key won't shut the engine down after that. I'll try to bridge the diode and see if that has any effect on my hyper ammeter.

And I'll PM Mike Winters.

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 Post subject: Re: Ammeter bounce
PostPosted: Sun Aug 13, 2017 8:57 pm 
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Joined: Sat Jun 01, 2013 5:38 pm
Posts: 572
Location: Orange, CT
It's going to do that. I forget why but when I did mine the procedure was to bypass the ammeter. So mine's not reading anything. I think you need to run a new wire with a resistor if you want it to work.

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Nov/70 late series one HLS3014777 Sunshine Yellow 919


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 Post subject: Re: Ammeter bounce
PostPosted: Sun Aug 13, 2017 9:46 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
Not clear, say again?

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 Post subject: Re: Ammeter bounce
PostPosted: Mon Aug 14, 2017 8:17 am 
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Joined: Sat Jun 01, 2013 5:38 pm
Posts: 572
Location: Orange, CT
Frank T wrote:
Not clear, say again?

What I meant was when you use an internally regulated alternator the ammeter circuit in the harness no longer registers what it's meant to. What you're seeing is noise since that wire is disconnected from the original alternator wiring. If you want the ammeter to work you need to run new wires to the charging system. Or just bypass it like I did. All I did was take the leads off and screw them together. I re-used the rubber boots as insulators and put some electrical tape around them.

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Nov/70 late series one HLS3014777 Sunshine Yellow 919


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 Post subject: Re: Ammeter bounce
PostPosted: Mon Aug 14, 2017 3:14 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
I'm not picturing that in my mind. I'll have to meet you somewhere and let you show me what you mean.

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