Charging issues with Toyota style Denso Alternator

[billytuffnuts]

I had some issues with my 60 amp denso alternator with being able to put out enough power when my electric fan was running, especially at idle. The fan was pretty loud and you could hear the rpms drop at stop, similar to the common issue of headlights dimming at idle. Idle @ ~900 RPM (mild cam) voltage was around 12.5-13 volts without fans/headlights and about 13.5 at 2000+ RPM

Anyways the alternator bench tested good (autozone) so I decided to upgrade to a 170 amp version and 4awg B+ cable thinking the 60 amp just didn't have enough to keep the fan powered at idle. The test report I received with the alternator states it puts out 80 amps at 833 rpms.

I Hooked everything up and I'm still having the same issue, except at 2000+ RPM the battery voltage increased to 14.5 volts. I've also checked voltage at the alternator B+ terminal with similar values so I don't think its a voltage drop issue.

• Sense wire to Starter Relay B+ terminal
• Switched 12v IGN spliced to Electric Choke wire
• Lamp - Not used
• Ammeter Bypassed

I've also had the battery tested which was deemed "Good" although they mentioned it's "towards the end of its life. Sounds suspicious.

In addition to the battery I'm also wondering about the engine pulleys: Using March underdrive pulleys on the water pump, crankshaft, and P/S pump - but not on the alternator itself.

Any thoughts on what I might be missing here?

 

[72bluNblu]

What electric fan?

The battery either checks good or it doesn’t. The whole “near the end of its life” thing sounds like a salesperson trying to sell you a battery. It could be lower voltage than it should be, but that could just as easily indicate a charging problem. If the voltage is low you have to rule out a charging issue. Or buy a battery and cross your fingers, because if it’s a charging problem that won’t fix it.

Also consider the fan motor could be on its way out, overheating and drawing too much power.

I run my ford contour dual electric fans with a 100 amp Tuff Stuff alternator, not even a Denso which should have a higher output in lower rpms. I can understand the 60 amp possibly not being enough at idle especially when the fans first kick on, mine draw between 30 and 40 amps at start depending on who you ask. But 80 amps at 833 rpm should be more than enough.

The underdrive pulleys could definitely be an issue. Just because the alternator pulley is standard doesn’t mean much, it’s all about the ratio between the crank pulley and the alternator pulley. If that ratio isn’t stock or close to it, that could be the issue as the alternator will be spinning slower and you’d get a lower than rated output.

 

[pishta]

your underdrive pulleys are working against the alternators RPM. Try a smaller pulley on the alternator. What is your estimated alternator shaft speed with your underdrive pulleys (OD of crank pulley / OD of alt pulley X RPM = shaft speed)

Pretty close to your output, this is a Denso graph.

 

[billytuffnuts]

What electric fan?

It's a 2 speed fan out of a early 90's Volvo 940

The underdrive pulleys could definitely be an issue. Just because the alternator pulley is standard doesn’t mean much, it’s all about the ratio between the crank pulley and the alternator pulley. If that ratio isn’t stock or close to it, that could be the issue as the alternator will be spinning slower and you’d get a lower than rated output.

your underdrive pulleys are working against the alternators RPM. Try a smaller pulley on the alternator. What is your estimated alternator shaft speed with your underdrive pulleys (OD of crank pulley / OD of alt pulley X RPM = shaft speed)

I looked into the pulley sizes & ratios and believe this is definitely the issue

Crank Pulley dia= 5.25"
Alt pulley dia= 2.63"
Ratio: 2:1

I looked again at the test report and they used a ratio of 3:1 (probably correct for a late 80's 4Runner). 80 amps @ 2500 RPMs (alt speed) / 3 (ratio) = 833 RPMs (Engine Speed).

With my actual pulley ratio of 2:1, at my idle speed I'm only pulling about 30 amps...

I'm not sure what the stock crank pulley OD is but bouchillon lists one with an OD of 7.375 and would get me to a ratio of 2.8. If my idle speed is around 900 RPM that should get back around 80 amps.

 

[pishta]

yeah, thats the problem then. 900 rpm (at idle?) is only 1800 alt RPM @ 2:1, putting out 30A...your boggin'!

 

[72bluNblu]

It's a 2 speed fan out of a early 90's Volvo 940





I looked into the pulley sizes & ratios and believe this is definitely the issue

Crank Pulley dia= 5.25"
Alt pulley dia= 2.63"
Ratio: 2:1

I looked again at the test report and they used a ratio of 3:1 (probably correct for a late 80's 4Runner). 80 amps @ 2500 RPMs (alt speed) / 3 (ratio) = 833 RPMs (Engine Speed).

With my actual pulley ratio of 2:1, at my idle speed I'm only pulling about 30 amps...

View attachment 1715545466

I'm not sure what the stock crank pulley OD is but bouchillon lists one with an OD of 7.375 and would get me to a ratio of 2.8. If my idle speed is around 900 RPM that should get back around 80 amps.

Your other alternative would be a smaller alternator pulley. Changing the crank pulley would change ALL of your pulley ratios, so that might mean all new pulleys. If everything else works fine changing the alternator pulley would be easier.

Are you running a v-belt or serpentine? March makes serpentine alternator pulleys down to 1.676, even with your current crank pulley that would be 3.13:1. V-belt down to 2.125, so that would be 2.5:1. Not all of them may fit that alternator but there are options.

 

[billytuffnuts]

Your other alternative would be a smaller alternator pulley. Changing the crank pulley would change ALL of your pulley ratios, so that might mean all new pulleys. If everything else works fine changing the alternator pulley would be easier.

Are you running a v-belt or serpentine? March makes serpentine alternator pulleys down to 1.676, even with your current crank pulley that would be 3.13:1. V-belt down to 2.125, so that would be 2.5:1. Not all of them may fit that alternator but there are options.

It's a V Belt setup, 15mm bore. After quite a bit of searching I was able to find a 2" OD pulley to give me a 2.625 ratio. Based on the report above, I should be in the 65-70 amp range which I think will be ok.

 

[billytuffnuts]

Update:

I received the new pulley and quickly realized I had a problem. The OD of the recessed area (where the flanged nut sits) on the new pulley is a little over 29mm. With the 22mm pulley nut that came with the alternator, all of my 22mm sockets were too large too fit inside the recessed area

Original vs. new pulley

OD of Craftsmen 22mm Socket

New pulley installed with original 22mm nut (hand tightened only)

After a long internet search I came across a fastener supply site that carried a 19mm nut to fit the 14x1.5mm alternator shaft. A 19mm socket was small enough to fit inside the recessed area and actually tighten the nut.

New pulley installed with new 19mm nut (torqued)

Finally reinstalled everything and its now charging between 13.5-13.8 volts at idle speed and 14.2 at a fast idle. Not great at idle but certainly much better than before the alt pulley swap.

I'm going to see how the car performs driving around town and at stop lights and make a decision on whether I need to consider going back to the stock diameter pulleys (crank/water pump).

 

[goldduster318]

Anything more than 12.8V (voltage of a 100% charged battery) under all the loads is just fine, since this isn't a police car or something where it will idle all day.. I'd say your problem is solved.

Another question would be what gauge wire goes from the stud on the alternator on it's path to the battery? It should probably be 6 ga for that high output of an alternator but you might be able to get by with 8. If it's 10 or smaller the wire will almost certainly be causing a voltage drop.

 

[billytuffnuts]

Anything more than 12.8V (voltage of a 100% charged battery) under all the loads is just fine, since this isn't a police car or something where it will idle all day.. I'd say your problem is solved.

Another question would be what gauge wire goes from the stud on the alternator on it's path to the battery? It should probably be 6 ga for that high output of an alternator but you might be able to get by with 8. If it's 10 or smaller the wire will almost certainly be causing a voltage drop.

I suppose it’s because I always seem to get an uneasy feeling when I come to a stoplight and see everything dim slightly, turn signals start blinking slower, etc...that I think the car is going to die but maybe you’re right.

I am running 4AWG cable from the alternator B+ stud to my inline fuse and then to the starter relay. Voltage drop across this circuit is about 0.10 volts.

 

[goldduster318]

I suppose it’s because I always seem to get an uneasy feeling when I come to a stoplight and see everything dim slightly, turn signals start blinking slower, etc...that I think the car is going to die but maybe you’re right.

I am running 4AWG cable from the alternator B+ stud to my inline fuse and then to the starter relay. Voltage drop across this circuit is about 0.10 volts.

Cool, yeah, I think you are good.

To put this in perspective, I have a 2012 Chevy Cruze, and it has a "low charge mode" where the computer senses the battery is full and then will change the alternator output even while moving down the road to 12.8V. This has the same effect, slow windshield wipers, etc. When it needs to charge it goes back up to a higher voltage.