Charge Ckt

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COS80

COS80

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Looking for some electrical understanding regarding the charge light circuit. The purpose of the question is in regards to using a diode in place of the charge fuse to trick the alternator into making slightly more voltage, which is supposed to be beneficial for AGM batteries. I tested this, but it did not work, presumably due to "current leakage" between the main and secondary batteries, or because of wire Y-L *2 not being present in 100 series LC. I'd still like to raise the alternator voltage, and I though perhaps a second diode on the secondary battery would create the effect.

If the picture below is illegible, it's p. 60 in the 97 LX450 EWD. I don't understand how this fuse works at all... it looks like Y-L *2 is a parallel bridge around the fuse, so what does the fuse do? Why does this fuse work at all with the parallel in place? Is the light tripped by whatever change in resistance that the loss of the fused leg would create when the fuse blows?

I haven't started looking for a 100 series EWD, but does anyone know if the 100 charge ckt also has this two-wire fuse approach?

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So now without that to fixate on, I realize that the batteries aren't even in the circuit, so adding a second diode isn't going to do anything. Anyone have an idea of why this approach works in a single battery 100 but not my dual battery 80?
 
I haven't attempted any msmts. The charge light is the indicator of correct operation with the diode installed (if the light is on with the engine running, it's backwards). My light comes on before starting the engine, but it does not seem.to come on while running without the fuse, which I understand is not the way it should work. I tried the diode both ways, and it neither raised the voltage nor turned on the battery light on the dash in either position. Patch suggested that my dual battery setup may be connecting the alternator to the starting battery in two places, which I have not confirmed.

I had to go back to emails from a year ago on these details, and I gave the diode to a friend of mine with a 100.
 
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You need to measure the voltage at the alternator. I wouldn't trust the dash gauge.

Normally, the charge light should illuminate only when the engine is not running.

The charge light will go out once the alternator is spinning and producing voltage, unless you have the diode backwards.
 
COS80 said:
The purpose of the question is in regards to using a diode in place of the charge fuse to trick the alternator into making slightly more voltage, which is supposed to be beneficial for AGM batteries.
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The alternator has a integral voltage regulator that (wait for it) regulates the output voltage to a max of 14.4 VDC, depending on the state of charge of the battery. In order to boost the output voltage, you would have to change the specifications of the voltage regulator.
Alternatively, you could install an alternator specifically made for higher voltage output.

FWIW, I've been running AGM batteries (Odyssey and Interstate) for years without issue on a stock system.
 
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jonheld said:
The alternator has a integral voltage regulator that (wait for it) regulates the output voltage to a max of 14.4 VDC, depending on the state of charge of the battery. In order to boost the output voltage, you would have to change the specifications of the voltage regulator.
Alternatively, you could install an alternator specifically made for higher voltage output.
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If you're meaning the diode doesn't work at all, it does, in my friend's 100 - just not in mine for some reason.

I thought about a custom regulator but not sure where to even start. There are no.alternator/starter shops anywhere near me.
 
COS80 said:
If you're meaning the diode doesn't work at all, it does, in my friend's 100 - just not in mine for some reason.

I thought about a custom regulator but not sure where to even start. There are no.alternator/starter shops anywhere near me.
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Does the 100 Series use the same alternator with the same specifications as an 80 Series?
 
jonheld said:
FWIW, I've been running AGM batteries (Odyssey and Interstate) for years without issue on a stock system.
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Just saw this edit. So have I, except I do have periodically charge them. Then there's this:

https://www.optimabatteries.com/charging said:
Voltage measurements of the battery when the engine is running are the output of your alternator. This measurement should be about 13.3 to 15.0 volts, which may differ due to temperature. At average operating temperatures of 50° to 80°F, your alternator output voltage should be about 14 volts to 14.8 volts.
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Mine runs as low as 13.5V on really hot days, but 13.8V is typical. This diode trick only raises V by 0.5 to 0.7V, IIRC, so a regulator would be a better choice, but the mystery of why it won't work just in my truck remains.
 
COS80 said:
I have a 130A Tundra alt w/Photoman bracket. It behaves per the same spec as stock, but I don't know how to tell what the regulator is set for, short of disassembling it.

View attachment 4108513
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You would need to measure the voltage at the output of the alternator after startup.
Again, alternator voltage will vary with state of charge of the battery. That's the "sense" wire.
 
jonheld said:
You would need to measure the voltage at the output of the alternator after startup.
Again, alternator voltage will vary with state of charge of the battery. That's the "sense" wire.
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That's 14.0V, maybe maybe 14.2V (going by memory). Electrical system is disconnected right now.
 
COS80 said:
Just saw this edit. So have I, except I do have periodically charge them. Then there's this:


Mine runs as low as 13.5V on really hot days, but 13.8V is typical.
Click to expand...
I monitor system voltage through my UltraGauge, so it's not the same as measuring at the alternator, but the only times I see anything below 13.7 is after a long drive. Typically it's sitting around 14 and change.
The only time I had to charge an AGM is when I left my York compressor engaged overnight. LOL, I actually did that twice before I moved the switch into the cab.
 
COS80 said:
Just saw this edit. So have I, except I do have periodically charge them. Then there's this:



Mine runs as low as 13.5V on really hot days, but 13.8V is typical. This diode trick only raises V by 0.5 to 0.7V, IIRC, so a regulator would be a better choice, but the mystery of why it won't work just in my truck remains.
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I was looking at the charging circuit, and if you add a diode to the sense wire (anode towards the battery), the voltage regulator will "see" about a .7 voltage drop which in theory will boost the output voltage of the unit.
However, adding a diode to the charge lamp side will do nothing. That lamp is supposed to light when the regulator voltage drops below the battery supply voltage. That's pretty much all that side of the circuit does.
 
jonheld said:
I was looking at the charging circuit, and if you add a diode to the sense wire, the voltage regulator will "see" about a .7 voltage drop which in theory will boost the output voltage of the unit.
However, adding a diode to the charge lamp side will do nothing. That lamp is supposed to light when the regulator voltage drops below the battery supply voltage. That's pretty much all that side of the circuit does.
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Where exactly are you suggesting? I'm not sure where the sense wire is (I thought this was it). I searched the EWD for "sense" before I left for work, and nothing came up.
 
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