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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars

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Alternator option

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Old Dec 28th, 2017, 21:31   #1
Noddy 123gt
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The alternator in my 123 gt appears not to be working properly. I have taken it to a local repair shop who maintain its ok. When its wired up I get 4.5 volts hanging around the amp and oil lights with the ignition off these lights are dim when the ignition goes on the light brighten to what they should be. I have changed the voltage regulator but this makes no difference. The alternator is showing 12v at the red wire on terminal 61 I don't think this is right also the alternator has a very slight heat on the casing.

I am of the opinion ( with my limited electrical knowledge ) that it's done and a new one needs to be purchased. I have rewired the car wth a new loom and everything is working ok except the fuel gauge, that will need a bit more thought and I am sure it will be easily resolved it shows full.

What is the best one to get is it one with or without the built in charging regulator 55 amp.

The old alternator has been out the car for several years.

Thanks
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Old Dec 29th, 2017, 08:15   #2
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Hi
I have had one of these fitted for a number of years. Small, super reliable, easy to hook up.
Self regulated so no need for the voltage regulator.
Needs to be mounted with spacers to ensure it aligns with the front pully. The excite wire is looped into the output, plenty of guides on the web.
Loads of options, i have the 40amp unit as im not driving a huge amount of kit but there are 100 and larger units available.
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Old Dec 29th, 2017, 09:17   #3
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Before you do anything more check all your earth connections. Make sure they are clean tight and bright.
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Old Dec 29th, 2017, 12:32   #4
Derek UK
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Note that the correct alternator for a 123GT is a Motorola and needs its own matching regulator. Mixing Motorola and Bosch won't work. Easiest to go Bosch with Bosch.
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Old Dec 29th, 2017, 15:47   #5
Ron Kwas
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Noddy;

The "local repair shop" has no reason to lie to you, but ask for details how they are energizing it and what kind of VRegulator they are using (or simply giving it full field with a test lead). Alternator and VReg work together as a "Charging System".
"When its wired up I get 4.5 volts hanging around the amp and oil lights with the ignition off" (something is clearly wrong there, but I don't think with Alt...I'd start at Ign Switch) "...lights are dim when the ignition goes on the light brighten to what they should be"(?).
"I have changed the voltage regulator but this makes no difference." (VReg must be the correct one as Derek mentions.) The alternator is showing 12v at the red wire on terminal 61 I don't think this is right (There should be Bat V on Term 61 when Ign is ON and Fuse 1 is intact! See below!) also the alternator has a very slight heat on the casing. (Probably nothing to worry about at this time, and under low Load.)

Here is an Excerpt of the 123GT Wiring Diagram to help with troubleshooting:

Notes and Functional Description:
Ign Sw supplies Ign Pwr to Term 61 (and VReg monitors this voltage) of Alt by way AMP Ind, daisy-chain connection to other Ign Pwr Loads, and of Fuse 1 (Important: F1 and associated connections must be intact for Chg Sys to function!).
When VReg senses a low sys V, it enables Alt output by enabling Alt Field Current (this is where I'm not absolutely certain if it is by "supplying power side" or "sinking low side" which is more typical...and this may differ from Motorola to Bosch units [that's why it also important not to mix and match VRegs!]...maybe someone who is intimately familiar with internals of Mot and Bosch Alts can clarify/verify here!).
Output of Alt at B+ is routed to Bat by way of Sec FB. [It is important never to intentionally disconnect Alt output from the rest of Sys even for test purposes...as voltage can soar to damaging levels! Do Not run Alt with No Load! See: http://www.sw-em.com/123GT_Reliabili...mprovement.htm

AMP Ind Function: Before motor is started and Chg Sys has output, one side of Ind gets Ign Pwr and Term 61 sinks power to light AMP Ind. Once motor is stated and VReg enables Alt output, Term 61 stops sinking Ind power and Ind extinguishes (has 12V on both sides at this time!).
As with Generator based Chg Systems, two very different conditions can cause Voltage across AMP Ind and cause it to light up:
1. No Chg Sys output.
2. Open F1 (but open F1 will result in no Chg Sys output!...and with the well-known FB and corrosion issues, this would be particularly important place [as all the other connections on Wiring Diag ] to assure good connections! Ref: http://www.sw-em.com/gastight.htm )

I suggest you connect a voltmeter to Bat to monitor Bat/Sys V, start engine, raise idle to get Chg Sys output. Before starting, meter will show Bat V after starting, Bat V should rise as Chg Sys contributes its output to Sys and charges Bat. If it does not rise, Chg Sys has no output.

Hope this helps and is not too much, but this is not a yes/no question!

Good Hunting!

Last edited by Ron Kwas; Dec 29th, 2017 at 15:54.
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Old Dec 29th, 2017, 21:19   #6
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I don't quite understand the description of the problem here Noddy. Are you saying that the amp light stays on when the ignition is switched off? If that's the case, then I would say that the voltage regulator is the wrong type or is buckered.

In basic, BASIC explanation, the voltage regulator has a click-clack switchover in it: when the engine's running, it clicks into the charge position. When the engine's off and the alternator's not charging it clicks into the non-charge position. If this function fails and it stays in the charge position when it's not running, the amp light stays on. All this can happen even if the other function of the regulator - that's to regulate the voltage - is working proper job, which in your case it seems to be as it's charging and the headlights brighten off idle, if that's what I think you're saying.

My apologies if the above explanation is too low level, but I hope it makes sense.

Usually, if the amp light is on when the engine's off, the battery goes flat very quickly. I have no experience of voltage regulators on Amazons with alternators, but I do with Amazons with dynamos which have the same voltage regulators as Beetles. The click-clack functions in those tend to deteriorate with a build up of corrosion on the terminals and can be put right with a clean up.

As mentioned 2 or 3 times above - are you certain you have the correct voltage regulator to match the alternator?
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Old Jan 5th, 2018, 16:34   #7
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Noddy;

I have compiled additional notes on the 123GT (Alt) based Charging System here: http://www.sw-em.com/123GT_Charging_System_Notes.htm

...hope the info helps!
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Old Jan 5th, 2018, 22:08   #8
Noddy 123gt
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Ron, thanks very much I haven't been back to investigate any further as yet.

This forum is great me I appreciate all the responses.

Thanks
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Old Jan 25th, 2018, 20:09   #9
Noddy 123gt
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New alternator fitted with built in charging regulator and all working now.

Thanks for the help and advice much appreciated
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Old Jan 25th, 2018, 20:46   #10
simon roberts
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Can we have a picture showing the connected wiring please?
Many thanks
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