I have a dual battery set up in my truck. I also have a 130 amp alternator upgrade from a toyota tundra 4.7L v8. Couple weeks ago my battery light came. I found that my battery isolator failed so i replaced it. Driving home the other night my battey light came on again. Voltage drop on the battery is 11.92 volts (its a brand new battery). Voltage drop at the isolator is 1v. Voltage drop at the alternator is 1v. When i rev up the engie the battry light goes off on the dash as soon as rpms drop down again the light goes back on. Had the alteranor bench tested at two auto parts stores. Both stores said the alternator is good. Any ideas? thanks in advance

 

Also i forgot to mention i have a wire split of from the signal lead wire on the alternator connection that goes on the delcotron connection on the battery isolator

 

Alternator should put out between 13.5V and 14.5 when engine is at operating rpm. Alternator has output that ("L" I believe, but may be different on T100) at 12V when alt is working fine. When batt/alt voltage goes outside that range while ignition is on, "L" output goes low and provides ground to Batt/Alt light.

What's your batt voltage when rpm drops? Does it go lower than 13.5V? If it does, that's why your batt /charge light fault light comes on.

Your alternator may be fine but maybe two batteries are just to much for it. Tried running with auxiliary battery and isolator disconnected?

Would be very helpful to monitor charging current with a clamp-on ammeter. Don't want my nice Fluke in the rough and tumble world of the 4Runner so I Got this from HF.

If current coming out of your alternator is less than rated 130Amps, Voltage is between 13.5-14.5V, but "L" output is low then alternator is bad.

 

maybe the alternator isn't putting enough amps out at idle. Time for a smaller pulley

 

ok i have to double check on that wiring L might be the light signal not sure. I cut apart a lot of my wiring harness and could not find any broken wires or anything like that. I do have a wire that t's off from the L terminal (or at least i think its L terminal) wire onto the delectron connection on the alternator which i though could of been bad wiring. I will fix that wire tomorrow. If i by pass the isolator would the wire from the alternator connect to positive side of the battery?

 

I will run more tests in the morning and i will keep you updated

 

cccp,Yes, please verify your schematic. IF it's same as older yota's charge light bulb should have steady +12V on it's positive side. It's "negative" side would be connected to "L" output of Alt. During normal operation, "L" would be +12V so no potential difference across charge light. When there's a fault, "L" goes low (i.e., around 2V). Now you have difference between two sides of charge light so light comes on.

I'm not familiar with Isolator. It may be less work to first measure current output of alt with isolator & aux battery connected, then IF current exceeds alt capacity, temporarily wire like stock to see if the second battery is causing overload.

Best wishes.

 

If i by pass the isoltaor would i just hook up the cable from the alternator directly to the positive side on the battery?

 

Gotta check your schematic. Look for where the alternator "B" output (thick wire) connects to battery. It's usually among/in between the fusible link and fuses.

"B" Charging output of alternator:



Typical alternator pin-outs:

L - charge Light. Normal operation 12V. Fault condition L goes low. When L is low charge light on.

"B" is charging output. Thick wire, Connect to battery among/in between fusible link and main fuses.

"IG" excitation current for stator.

 

ok so i just got back from working on the truck again. After fixing my wire on the S terminal (it looked like it was pinched) I first wired the alternator terminal B on the isolator and tarted the truck when it first started the battery light dimmed out and went out for a second or two but than came back on. bringing up the rpms made the light go out. I than checked the voltage drop at the battery it was at 11.92v. Voltage drop at the isolator is 1.1v and voltage drop at aternator was at 1.1v. I than brougt up my rpms up and checked the voltage drop at the battery it went up to 13.92 volts. At the isolator it was at 13.95v and at the alternator it was at 13.95v. The battery light still is staying on. I by passed my isolator and connected terminal B from the alternator directly to positive side of the battery voltage drop at the battery was at 13.95 and at the alternator 13.96v. The battery light is still on and now it does not matter if i bring up the rpms up or not the light is on constatly

 

Hi cccp, is voltage drop at aternator was at 1.1v. the voltage you're getting at "L" output voltage? Would be nice if you could post schematic of your truck. If "L" output remains that low, even if your alt is putting out between 13.5V & 14.5V (possibilities):

• Regulator/internal electronics of alt is bad.
• Regulator is OK but something is loading (almost short circuit to ground) "L" output and forcing it to go that low (less likely, but still possibility).

 

This is what kinda threw me off when i first checked the voltage drop at the alternator it was at 1.1v but after reving up the engine it went up to 13.96 v and thats where it stayed after i brought the rpms down. I could not get it to read 1.1 v after that. Everything seemed ok like the alternator was charging but the light is still on. The battery gauge is reading normal range. I will try and pull up a wiring diagram

 

here is a write up from another site on how to upgrade the alternator http://forum.ih8mud.com/80-series-te...0-amp-pdf.html

 

this is the wiring diagram for the alternator hope the link works

 

No schematic? Need schematic that shows how Alt ("L" output) connects to charge light circuit.

 

Uploaded with ImageShack.us

 

keep in mind that my connector is different because of a different alternator but the wire colors are the same or at least i think so got to to double check that

 

Now we're talking

Please see my notes...


Here are important points to check:

With ignition off, F should be 11.92V

Disconnect connector EA1.

Leave EA1 disconnected. Ignition on, engine running:
With EA1 disconnected, charge light should be off.
If charge light stays on with EA1 disconnected, check Voltage at "E" or "C". Should be high or 12V. If low:

• Look for shorts to ground.
• Makes sure nothing is connected to negative side of charge light-diode circuit.
• Check for any after-market wiring connected to negative side of bulb-diode circuit (eqpt that only come on when IGN is on like DRL).
• IF Canadian model, also disconnect connection from dDRL circuit to isolate problem.

1) Measure current through thick white output wire (B) with clamp-on ammeter (Harbor Freight is your friend ) Should be within capacity of alternator.
2) Measure volt @ F. Should be between 13.5 & 14.5V.

Measure "D" = "L" output:

• If 1&2 good, D should be 12V. Reconnect EA1. Charge light should stay OFF.
• If If 1&2 good but D is low, IC/regulator bad. Replace alternator.

If 1 good, but 2 bad, = bad regulator/alternator.
If 2 exceeds alt capacity- check for shorts, possibly bad battery...

More details if you wanna to analyze ...

Normal operation condition:

A: 12V nominal when ignition on.
B: ALT output 13.5 to 14.5 V
E (=voltage "L") = 12V when ignition on
Volt@A - volt@E = 0 =>> no potential difference across charge light & diode =>> charge light OFF.
F = batt voltage: 11.92 With ignition OFF. 13.5-14.5 V with charging circuit running normally.
IG: (supplies current to stator to regulate output): 12V nominal when ignition on
S (sense voltage: feedsback abbt V to regulatr so regulator cna adjust.
( I think schematic is poorly labeled. The "B" pin connected to regulator should be "S" for sensing battery voltage as feedback to regulator.

Fault Condition:
A: 12V nominal when ignition on.
E: low, approx 2V? 1.1V?
Volt@A - volt@E =/~ 10V = Potential diff across charge light & diode => current flows => light ON

 

thanks a lot i will run more tests when i have some free time and i will keep you posted

 

and i do believe that is an S on the wiring diagram just smudged up or something