Another voltage/alternator issue

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candymancan
Posts: 3652
Joined: Tue Mar 22, 2016 11:32 pm

Another voltage/alternator issue

Post by candymancan »

Like alot of you i have had this issue day one on owning the Jeep, you are in drive, at a stop and with the headlights/fogs on the Jeep simply cannot get enough voltage/amperage to the accesories/lights/turn signals are slow. Switching to a bigger alternator didnt fix it, going to a huge battery didnt do anything, upgrading and replacing the power/negative wiring didnt do anything.

My wagoneer has a 90 AMP alternator on it brand new within the last year, and the old one did the same which was a 76AMP i think ? somewhere around there, and with the engine at 600 to 650rpms in drive the alternator simply cannot get the voltage needed to the headlights, blinkers, fogs and blower motor, and the volt meter on the dash shows it well under the 13v line. I tested the voltage at the battery and it shows well over 13.5v but down the chain it drops. If i crank the rpms up to 750 or so idle then i have no voltage issues with the headlights/a.c on, its always right at 13v and the blinkers are blinking fast and the headlights arent dim. It gets worse when the a/c is on, with the compressor on the rpms drop about 50-100rpms and power is redlined. So i need to keep the engine idle higher to compensate


I dont think the alternators im using can supply enough power/amps to the Jeep at lower RPM's. The problem with keeping the RPMS at 750 in drive, is when i go to park its above 1,000 rpms. Around 1100. If i drop it down to 600-650 like it should be in drive, in park its around 900 rpm. Also when the rpms are too high above 1000, the engine will diesel on me when i shut it off, which you never want to happen. So im stuck, keep rpms lower where they should be so it doesnt diesel and simply rev too high in park, or keep them higher so i dont have power issues. I cant keep the rpms higher, which fixes the issue.. I dont want the engine to keep dieseling when i shut it off.


Is there anyway i could just remove the pully on the alternator and swap it for a larger/smaller one to supply more juice ? If so which gives it more power ? Smaller or larger pulleys ? And no it isnt my belts, all my belts are new the correct part numbers and its fairly tight, nothing is loose
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)

SJTD
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Joined: Tue May 21, 2013 12:02 pm
Location: Lompoc, Sunland or somewhere between

Re: Another voltage/alternator issue

Post by SJTD »

I don't get the problem with lights dimming at idle. How long do you spend at idle?

To increase the alternator speed you want a smaller alternator pulley or larger crank pulley. But then maybe it spins to fast when you're driving.

Engine speed times crank pulley OD divided by the alternator pulley OD gives you the approximate alternator rpm.
Sic friatur crustulum

'84 GW with Nissan SD33T, early Chev NV4500, 300, narrowed Ford reverse 44, narrowed Ford 60, SOA/reversed shackle in fornt, lowered mount/flipped shackle in rear.
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Another voltage/alternator issue

Post by tgreese »

An alternator makes 3-phase alternating current that's rectified to DC by a diode bridge. The voltage regulator controls the output voltage by controlling the current through the field windings. More field current, higher output voltage. If either of these don't work properly, the output will be compromised.

Popped diodes were very common with the Motorola alternators, and each open diode lowers the alternator output at idle. The regulator is a modular component and easy to replace with a low-quality low-cost substitute. You should be able to test performance of thes components - in the 70s and 80s the dealerships would repair these units, not swap them out. I'd check the TSM for step-wise diagnosis and repair instructions. At least you can determine that the alternator is performing properly.

I kinda think it's more likely that your replacement alternator has a problem than your pulley is spinning too slow.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

letank
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Re: Another voltage/alternator issue

Post by letank »

if you do not have a idle stop solenoid, install one and power the idle stop solenoid when the AC is on or the headlights are on, thru a relay. Then when you turn off the engine, the relay will be off and so will the idle stop solenoid, and no dieseling which was the attribute of the idle stop solenoid
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

hanger
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Joined: Sun Dec 16, 2018 8:09 am

Re: Another voltage/alternator issue

Post by hanger »

Where can you buy one of those? Never heard of a idle stop solenoid.

rocklaurence
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Re: Another voltage/alternator issue

Post by rocklaurence »

May be your resistive Regulator wire is too short-too long? I dont if you need to add or subtract resistance to increase the alternator output. Or your alternator belt is loose? A larger OD crank pulley will speed up all your accessories
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Another voltage/alternator issue

Post by tgreese »

The resistance wire does not affect voltage regulation. As a resistance, it sends a trickle of current to the alternator at start-up, enough so it can self-generate at low speed. Its main purpose is to prevent backfeeding of voltage to the ignition once the alternator self-generates. It either works (engine stops when key is turned off) or it doesn't (engine keeps running with the key off).
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: Another voltage/alternator issue

Post by letank »

hanger wrote: Thu Sep 05, 2019 7:43 pm Where can you buy one of those? Never heard of a idle stop solenoid.
summit has them

https://www.summitracing.com/search/par ... d-brackets

but I have not found an exact replacement, and you need the matching bracket to the carburetor

you can see it on the right bottom side of this pict

Image

it is a ford carburetor, so ford part, so you be lucky with these refs,

https://www.ford-trucks.com/forums/8154 ... enoid.html

or ebay, it looks like ours, w matching bracket

https://www.ebay.com/itm/MOTORCRAFT-215 ... -1&vxp=mtr
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)
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