Are these Voltage readings OK? Considering Alternator Upgrade? (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Dissent

Questioning my life choices...
Joined
Sep 27, 2012
Threads
265
Messages
3,754
Location
Sweetwater, TN (East of Knoxville)
I need some assistance/clarification/comparison to dtermine if I need to improve my OEM 80A alternator to a 150A Sequoia alternator. I'm 1/2 way to the Sequoia, I have all the parts from Photoman, just need the actual alternator. Before I buy it, however, I need to validate the alternator is the issue.

I seem to be draining the battery faster than it can fill based on my assessment this afternoon. Wheeling trips at idle/low speed RPMs with the A/C running result in a resting battery of about 12.7v at the end of the day with the solar panel pumping in 4.4A all day. Late night with minimal LED light usage I see 12.6-12.5v. Starting isn't an issue the next day.

Daily driving is 32 miles each way, the truck sits in the sun all day charging.

I never see 14.4v anywhere. The best is 13.8 and the average is 13.8 on the freeway. Sitting in traffic idling is 12.3v typically running the LCP fan, Alpine amp and A/C on high, sometimes the headlights are on too.

I know modern vehicles read about 13.7-13.8v at idle and 14.4v on the freeway. I've never seen that with a new alternator AND battery.

I had a series 31M Diehard Platinum (AGM) 4 years ago which died shortly after my original alternator died. I replaced the battery with a Diehard Gold (standard wet) with the 6 month old alternator and have seen the same results for the past 3 years.

Below is my list of improvements and test conditions. Any help would be greatly appreciated!

Improvements:
  • Big 3 2AWG Cabling (225A rated) - Battery Ground to Frame, Battery Positive to Alternator, Alternator Ground to Battery
  • 500W Alpine amplifier
  • LCP Radiator Fan (LX470 fan)
  • Toyota OEM re-manufactured alternator 3 years ago
  • Sears Diehard Gold OEM size battery 3 years ago
  • 100W Renogy Panel and MorningStar PWM 30A Solar Charger

Battery Cable Ohm Readings:
  • Battery to Alternator - 0 ohms
  • Battery to Frame - 0 ohms
  • Frame to Body - 0 ohms
Test Engine RPMs:
  • Idle (670 RPM)
  • Freeway Speed (2000 RPM)
Accessories Engaged:
  • Headlights
  • LCP Radiator Fan
  • Alpine Amp (normal listening and music choice)
  • Air Conditioner on High
Test Conditions:
  • Readings on Positive Battery post in sun with Solar feeding 4.4A (by accident)
  • Alternator is within .10v of all Positive post readings
  • Battery specific gravity is above 1.3v per cell
  • 100 degrees ambient, removed from 85 degree garage

Test Results:
  • 14.10v - Idle with no accessories at all
  • 13.5v - Freeway Speed with all accessories
  • 12.75v - Idle with all accessories
  • 13.35v - Idle only A/C and LCP Fan
  • 13.23v - Idle only A/C, LCP Fan, Alpine amp
  • 13.10v - Idle only A/C, LCP Fan, Alpine amp (heavy bass)
  • 12.85v - Idle only A/C, LCP Fan, Alpine amp (heavy bass) & Solar covered
  • 13.75v - Freeway Speed only A/C, LCP Fan, Alpine amp (heavy bass) & Solar covered
  • 13.0v - Sitting for 30 seconds after turning off key
Bottom Line:
  • 12.2-12.8v is what I typically see driving around town.
 
At the main battery terminals, you should be getting 13.5 to 14.4 volts when the motor is running at idle and nothing major light headlights is turned on.

If you're not, get the alternator itself checked out first. Simple things like checking the brushpack (brushes are designed to wear) and the condition of the sliprings are often the most common cause. Even a standard 80 amp alternator should take care of all basic elec requirements.

Not sure with the petrol motors, but with the diesel motors, the 80 amp original alternator can be replaced with a 110 amp one and the only things that need changing are the tensioning bracket (as the alternator body is bigger) and the later alternators use a flat sealed three-pin connector instead of a round connector so an adaptor cable may be needed.
 
Those numbers look normal to me. I run the @Photoman 150A Sequioa alt and have a dual battery setup. Both batteries sit at 13.2VDC resting. Per my Ultragauge, I run 13.8-14.1VDC driving on the freeway. I think the higest voltage I’ve seen driving is 14.4, and that was right after I started the vehicle after it sat for two weeks. For what it’s worth.
 
Sitting at idle with nothing turned on is typically about 13.45-14.1v. I'm never in that condition though and those 4 accessories are always running. Trouble is, monsoon season is coming up and I'll be adding wiper blades to that load...even at night.
My typical sitting in the garage, out of the sun, reading is 12.7-12.8. It's never in the 13.x range sitting for over a couple of hours.
 
Forgot the ARB 50 fridge...it's running on trips.
 
I played with this a bit last night and found that after a full night of charging, the voltage is not an issue. However, I have no idea what the amperage load is. I've been looking at the wrong factor. The alternator works fine. I loaded up beyond my normal load adding the rear defroster and the rear heater on high and the battery dropped to 12.2v and stayed there. I could hear the engine load while I turned these things on. When I revved it to 2000 RPM, it held steady at 13.7v indicating the alternator was putting out it's 80A rating.

I need to put an ammeter (clamp most likely) on the alternator and the battery load to see what's actually happening but suffice to say, I need these 80A at idle.

I'm 1/2 way to the 150A Sequoia conversion but now I need to know that it can put out say 80-100A at idle. Can anyone address this specifically?
 
Why do you need 80-100A at idle? Most alternators will not produce that at idle without putting on a smaller pulley, which has its own issues. That's why you would add a hand throttle.
 
The smaller pulley will pull a few extra amps from an alternator by spinning it faster. Ideally a 3:1 pulley ratio is perfect. If the truck idles at say 670RPM, the 3:1 ratio would put the alternator speed at 2,010 RPM which is fine for modern alternators but most legacy alternators don't really kick in until 2400 RPM.

I'm sourcing a clamp DC ammeter to get actual readings but I'm absolutely confident that my current draw at idle surpasses the OEM alternator output at idle which is why my voltage reading is so low at idle speeds with the following loads engaged: A/C blower on high, LCP radiator fan, stereo/amp, headlights. When i include windshield wipers, it gets even worse. The 110+ temps here during the rainy season require all of these running even at night when it's still 90+ degrees.

All modern alternators put out at least 100A at idle to run all these systems plus the 6-12 onboard computers. 100A at idle is normal in 2018, very uncommon in 1997.
 
Oh, and I have a hand throttle...
 
disconnect the battery and test the cells with an actual battery tester not multimeter. if you have overheated your battery it could kill it just after 1 time. I refuse to use wet cell batteries anymore. they go too quickly here because of the heat. its rare that a wet battery lasts for more than 3 years with heat...

one way to see if you need more is add up your normal load and if it more than 80% of the max rating of your alternator you need a higher rating alternator
 
Last edited:
also, its not uncommon for a battery to show normal voltage with a bad cell. seen it many times on the military generators while I was in. that was the reason we switched to optimas...
 
disconnect the battery and test the cells with an actual battery tester not multimeter. if you have overheated your battery it could kill it just after 1 time. I refuse to use wet cell batteries anymore. they go too quickly here because of the heat. its rare that a wet battery lasts for more than 3 years with heat...

one way to see if you need more is add up your normal load and if it more than 80% of the max rating of your alternator you need a higher rating alternator
I did test each cell (see below)...I don't think the battery is faulty. I had an AGM too but it died in about 1.5 years. Our OEM alternators aren't designed to properly charge AGM batteries but many use them without issue.

Adding up real amp draw numbers is on the list of things to do, when I get ahold of a clamp meter. That 80% threshold is what made me realize that 64A is what Toyota designed for, I've added at least 30A to that with my daily load. Considering the truck runs on the alternaotr (not the battery, it's only for starting), the stock specs show the alternator is too small at max output. I think the idle output is less than 30A if that. All my driving is low/slow speed during the week. I need all my amperage at less than 1000 RPM.

Test Conditions:
  • Readings on Positive Battery post in sun with Solar feeding 4.4A (by accident)
  • Alternator is within .10v of all Positive post readings
  • Battery specific gravity is above 1.3v per cell
  • 100 degrees ambient, removed from 85 degree garage
 
also, its not uncommon for a battery to show normal voltage with a bad cell. seen it many times on the military generators while I was in. that was the reason we switched to optimas...
I used to run Optimas exclusively and only went back to wet cell when the quality suffered. Tried AGM but it lasted less than my typical 3 year wet.
 
Here's a neat amperage quick calculator I found. Calculate the Amperage You Need

My initial run shows 206A required for all my stuff driving around town. Stripped down to just the car, A/C and the LCP fan shows 100A.
 
I doubt the alternator is ok if it’s under 13 volts when it’s running. I don’t think you’re pulling 200 amps. 200 amps is a lot, like as much as a 2000 watt RMS stereo would draw.
 
Keep in mind, it's a rough calculator.

This is a rough forum sometimes. I see a lot of push back to upgrade the charging system. Everything else on these trucks is upgraded as a matter of fact, usually to the point of exceeding ANY real world requirement. I'm not sure why 2+ batteries is blessed by all, primarily for winching, but a larger alternator for daily loads and drive-ability is met with blank stares and mutterings about one's mental stability. I realize that many 80 owners don't have any additional current draw but some do. I've moved this Alpine amp around the past 3 vehicles, all had 150A alternators and never had any issues. Now I've added a cooling fan for the radiator. I also run my headlights all the time for visibility. I also have to run my A/C and headlights and wipers at night during the summer. There are real world requirements that push the demand past the 40-50A OEM loads.

Why is there a 100A option for the 1998 LX470 (100 Series)? What changed where they needed additional amperage? One year later, there was a noticeable improvement. Nobody questions why the 2003 Sequoia comes with a 150A alternator, it's accepted and they move on. Nobody wonders why the 2018 Tundra has a 150A alternator. If the 1997 80A is more than sufficient, why did they increase it by 20A one year later and 70A 16 years later and maintain that value until today? Nobody questions these values because it's assumed that your car will keep up with the times. Time traveling 20 years into the future expecting antiquated tech to keep up is absurd. In the 70's a standard family car had a 40A alternator, the police cars of the day ran 100A alternators. Why is this? They only ran a couple of twirly lights with a siren and radio. Why would they increase the amperage? The higher end consumer models had the same high output alternators to keep up with the defroster/heater fans of course.

A hand throttle is a wonderful gadget to get the alternator to put out max amperage when the truck is sitting still. Great for winching and what not. I use it all the time to keep my radiator and A/C blower fan in the 13.5v range rather than the 12.4v range at idle. Driving in traffic is not great. If I had that amperage at 800 RPM (2400 RPM on the alternator) I'd be a happy camper. 1997 tech simply didn't deliver this. I guarantee you if you find a market with the 80 equipped with rear A/C and an OEM fan and whatever else draws power, it probably doesn't have an 80A alternator, I'd guess at least 90A to offset some of that equipment.

I haven't asked around but I'm sure the V8 conversion guys probably kept the 80A OEM alternator too. Why would they change it since it's more than sufficient? I bet there's not one V8 conversion running an OEM 80A alternator.

This is a great forum but the allegiance to the 80A alternator makes me scratch my head.
 
More amps is better but still you’re not drawing 200A and probably a fresh 80a would bring you at least over 13v. Even my truck charges at 13v at idle and I’m planning on replacing the alternator ASAP.
 
Here's a neat amperage quick calculator I found. Calculate the Amperage You Need

My initial run shows 206A required for all my stuff driving around town. Stripped down to just the car, A/C and the LCP fan shows 100A.
I'd like to see what you're including to come up with a 200A draw.

The categories on that calculator are far too vague to be of any use. Easiest way is to use a DC clamp meter with the engine idled up.
 
[QUOTE="Dissent, post: 11697017, member: 81471]"Keep in mind, it's a rough calculator.

This is a rough forum sometimes. I see a lot of push back to upgrade the charging system. Everything else on these trucks is upgraded as a matter of fact, usually to the point of exceeding ANY real world requirement. I'm not sure why 2+ batteries is blessed by all, primarily for winching, but a larger alternator for daily loads and drive-ability is met with blank stares and mutterings about one's mental stability. I realize that many 80 owners don't have any additional current draw but some do. I've moved this Alpine amp around the past 3 vehicles, all had 150A alternators and never had any issues. Now I've added a cooling fan for the radiator. I also run my headlights all the time for visibility. I also have to run my A/C and headlights and wipers at night during the summer. There are real world requirements that push the demand past the 40-50A OEM loads."[/QUOTE]

I agree with you. I don't understand the push-back. Its clear you need more output at idle. Before I replaced my headlight bulbs with LED I noticed my alternator couldn't keep up with the load if my AC or wipers are on. If a bulb could be replaced, I replaced it with LED. It helped a lot. I do have Photoman's 150amp conversion and a Denso 150A alternator waiting for my 80A alternator to crap the bed. I know that if I add any more load to the electrical system, which I will, it will require a higher output alternator to accommodate. Its pretty simple to figure that out. I think you're on the right track and 100% correct in your thinking.
 

Users who are viewing this thread

Back
Top Bottom