When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Long story short. Replaced faulty alternator (lg case 6g with Lg case 3g) been noticing 14.4 once GP ccycles off. But once driving for about 15-20 minutes. Voltage drops off to about 13.7. Sometimes as low as 13.5. Seems a little low to me.
Haven't checked voltage at batteries yet. I'll do that this evening. Just wanting a little feedback on what others think on the some what lower voltage readings I'm seeing. Is this normal or something I should be concerned about for fully chcharged batteries?
I'm not convinced it's a bad alternator. Your regulator will change voltage charge depending on needs or requirements.
To Bullit's point, it will also vary depending on where you measure that voltage. OBD, terminal on alternator, battery, etc.
When you see 14.4 volts, that's about the max that regulator will allow. I see mine dip into the mid 13's when fully charged. OBD will show lower, battery terminal will also be lower due to wire resistance between alt and batt.
Are you having issues now or just concerned with the numbers?
There is no ideal charge voltage. The regulator should put out what's needed. A fully charged 12v battery is 13.2 volts(6 cells 2.2 volts apiece). Depending on the load demanded the regulator will vary output. After the glow plugs kick on and shortly thereafter the batteries need to be recharged so voltage should increase. After the load from the batteries drops off the voltage should drop back down. As a general rule most floats on the battery will be 13.8 +/- a couple of tenths. Is voltage stays high all that does is gas the battery and usually causes plate flaking and electrolyte loss if demand is not there.
I'm not convinced it's a bad alternator. Your regulator will change voltage charge depending on needs or requirements.
To Bullit's point, it will also vary depending on where you measure that voltage. OBD, terminal on alternator, battery, etc.
When you see 14.4 volts, that's about the max that regulator will allow. I see mine dip into the mid 13's when fully charged. OBD will show lower, battery terminal will also be lower due to wire resistance between alt and batt.
Are you having issues now or just concerned with the numbers?
Just concerned with the numbers. All my readings are from the OBD port through my scangauge. I'll be taking readings from the batteries this evening. I consistently read 14.3-14.4 for the first 10-20 minutes of driving (on the first start of the day)
Then it varies from 13.5 to 14.0 throughout the rest of the day.
Going to turn all accessories on once warmed up and see what my values are this evening. I will add that i do have the smaller pulley installed 58mm and was looking for better higher constant voltage. But, as you stated. The regulator will go by supply and demand.
This 3G is supplying better first start idle voltage than my 6G large case that I took off.
Thx.
I too would expect a higher charging value after first starting with the starter motor draw and the glow plug demand.
I too would expect it to taper off once the batteries get that charging jolt.
If your batteries are fairly new, I again, would expect to see a lower charge rate after a few minutes of running.
I would test your batteries overnight with a vom for their static charge, then start up the engine and see what the charge rate is too validate the alternator effectiveness.
I wouldn't chase good money after bad just quite yet.
I think its working as designed. Just got a little nervous knowing how important the voltage is for these trucks. Going to spend a little time this weekend and check all grounds and clean the cables. Been wanting to upgrade to the big 3 wire upgrade. Maybe give Ed a call or make on up myself. Shouldn't be too hard.
Thor'sHammer I haven't checked my cables in a year either. Going to check'em all. Was that the passenger side cable that was bad? I just turned 166K on my truck. Time to give her the once over
When I know that the truck is going to be resting for a while
and the engine is cool I have a Schumacher battery charger
that would just freak you out with the charge voltage it puts
out. But once the battery reaches 100% it drops off to a float
charge state. I can tell you that the batteries seem to act much
better after a few cycles.
On the ODB2 port and the SGII I find that it lags the battery post
voltage by as much as 1/2 volt. When your talking battery health
it's the post voltage that really counts. That is why testing cables
is a good idea. The test you want to do is called a voltage drop test
