odd battery voltage

[Donald]

I checked the voltage on my new to me Bobcat (diesel) and it was 13.00V at the battery on 2 DVMs. The battery should be close to being fully charged but not 100%.

I ran the machine for maybe 1 hour and it does not appear the alternator is charging as the dash voltage gauge does not change from engine off to engine on.

The alternator is pretty new, I was told and is a self exciting single wire alternator (I think). I ran the engine to full RPM to "kick on" the self exciting alternator.

It has not been on an AC charger for a week.

 

[George7941]

If you have a DC amp clamp you could load the battery and see how much current the alternator is generating.

 

[JHZR2]

13V sounds like a surface charge on a fully charged battery, if it was at rest.

If the gen is on, sounds like a bad ground. Open ciurcuit voltage on the battery should be around 12.7V, especially after a glow and start. The fact that it is higher means to me that there is some voltage there, regardless of the current level.

 

[Donald]

The other minor to maybe major problem is the machine "creeps" even with the parking brake on. So at this point I cannot climb out of the cab with the machine running and would not trust my wife in the cab nor doing any measurements. Remember a Bobcat is 100% hydraulic so there is no "in gear" or anything like that.

But there is no way the alternator can be charging if the voltage does not go up to around 14 V and as I said the dash voltage gauge does not budge when the engine is running (from not running).

 

[wrcsixeight]

13 volts is a bit high for a rested, fully charged battery. Some people say 12.6 some say 12.65, I've even see some claim 13.7 as a battery's fully charged rested voltage.

I have a single ever start remaining out of my trio of batteries. It's fully charged rested voltage, even at 4+ years of age is 12.8.

I replaced 2 failed ever starts with 2 high quality Crown true Deep cycles, and these have a fully charged rested voltage of 12.6.

By no means does this lower, fully charged rested voltage indicate the everstarts were/ are a better battery, just that they have different fully charged resting voltages.

I've read some AGM batteries are 13.1.

I'd be more worried about the functionality of the alternator, and if that battery is reading that, I wouldn't worry, unless you tested right at engine shut down, instead of waiting for a long while.

It takes 6 to 8 hours resting, more or less, depending on temperature and battery for the surface charge to dissipate.

 

[bmwtechguy]

It's not clear from your post whether the engine was running or not when you measured the 13V. If that was measured with it running, then either the battery is very discharged and taking a lot of current from the alternator to bring it up to full charge, or the alt is not charging at a high enough rate for some reason. Check wiring from alt to battery for any high resistance connections. Use your voltmeter to measure voltage drop between any connections. You should get very little voltage drop with a typical 30 or 40amp charge. It is not uncommon to see only 13.5V output at the battery from one of these one-wire alternators after they get heated up from running a while. There is an internal voltage regulator that has a temp-sensitive diode that reduces charging voltage somewhat after the alt heats up. This allows a quick re-charge after a cold start, but then the charge rate tapers off some as the alt heats up.

 

[eljefino]

I was reading somewhere that you need RPMs *AND* a load to kick the things on. The diesel has no ignition load, and your battery is well charged. Do you have headlights and stuff?

 

[Donald]

Originally Posted By: eljefino
I was reading somewhere that you need RPMs *AND* a load to kick the things on. The diesel has no ignition load, and your battery is well charged. Do you have headlights and stuff?



If memory serves me right, with a single wire alternator, you need to go to a fast idle before it will go into self excite mode, after that it will charge at idle. It does have 3 kind of headlights.

The green light is flashing on my float charger this morning so it looks like the battery is fully charged. I will test the voltage in 24 hours.

 

[Donald]

A flooded cell battery that is fully charged and about 70F is 2.13 V per cell. After any surface charge has worn off. It simply cannot be anything more no matter the make/model, could be less if battery is not up to snuff.

 

[mechtech2]

At 13V, there appears to be some charging.
With the engine off, put your test leads on the battery posts. 12-12.5 is normal. Start her up and rev it to 1,500 or so. 14V should be produced. Voltages vary, but it should increase.

 

[eljefino]

I wonder if your alt "lost its magnetism." There might be a way to put it back in. DO SOME RESEARCH and don't take my word on it, but I BELIEVE you hook it up with reverse polarity real quick. Take appropriate safety measures against sparks and blowing up batteries.

Do you have an ignition switch? You would seem to, if you have a dash voltage gauge. With a switch you can run a two wire alt like you'd find in a normal 70s-90s era car (from before computers made things 20x more complicated.)

Might be easier to switch to a two wire alt. Advance auto has one for an 80's GM for $30-- and you can use coupons on that! This is apparantly the same case that they use for most of the "hot rod" 1 wire alts-- 10SI? So it could bolt up.

If you're real lucky, you might be able to take the cover off what you have, and access the field control directly.

 

[Donald]

So I fully charged it with an AC charger and let it sit 24 hours to eliminate the surface charge and the voltage is 12.78, basically snot on.

But I do need to look into the voltage with the engine running and the self excite alternator. There is something odd there.

 

[mechtech2]

Turn on lights for 15 seconds to eliminate the surface charge before taking a reading.
Or whatever makes a draw.