Charging voltage

[suntreemcanic]

Replaced the eight year old battery in my B7800. Before I removed my old battery I checked charging voltage and it was 12.4 volts. I installed my new NAPA Legend battery and it was still charged at 12.4 volts. I am waiting for my manual so I have to rely on you guys. My experience tells me 14.0 volts is a more desirable charging voltage. Does anyone know if 12.4 volts is maximum charging voltage for a Kubota B7800 or do I have a charging problem?

 

[number two]

You have a charging problem.
A fully charged 12 volt wet cell battery will test at 12.6 volts-2.1 volts per cell x 6 cells.
Yes,14 volts is about right.
Good Luck!

 

[CobyRupert]

^ This. I second number two.

 

[rswyan]

What engine rpm was the charging voltage measured at ?

 

[k0ua]

You have a charging problem.
A fully charged 12 volt wet cell battery will test at 12.6 volts-2.1 volts per cell x 6 cells.
Yes,14 volts is about right.
Good Luck!

After a startup the charging voltage may be around 14.0 to 14.2 or even a little more on some systems.
After a few minutes when the battery is becoming fully charged, the running voltage should be around 13.8 at any kind of normal RPM. At idle it may dip a little bit, and of course under heavy load it may dip down some, but even under full load, lights etc, it should not drop below 12. 6 in any way shape or form. At 12.6 the alternator is not charging the battery, but just keeping up with all the loads on the system, At 12.4 you are losing ground. Not only is the battery not being charged, it is actually discharging into the load. So the Alternator/voltage regulator is not functioning. Most modern alternators have the regulator built in to them. If all connections are clean and tight on alternator, grounds, battery terminals, and at say 2000 RPM, if you are not seeing at least 13.8 volts, you need to have that alternator tested. Many automotive shops will test them for a fee. A really bad battery might make the reading show that low, but I would think it would not crank the tractor the next time. It would be worthwhile to put your meter on another good working vehicle (your car or truck), and measure its resting voltage, and start the vehicle and watch its initial charge voltage, and after several minutes watch it come back down to maybe 13.8 or so. They all vary a little, but 12.4 if your meter is accurate is not going to work out for you.

 

[suntreemcanic]

I checked my volt meter against another vehicle and validated it was measuring properly. Measured voltage at new tractor battery after sitting all night 12.6 volts. Then turned on head lights for one hour, ran battery down to 12.1 volts. Started tractor, idled it for a while to get it warmed up then ran up to 2,000 RPMs. Started out at 12.4 volts charge then after a couple minutes worked its way up to 13.6 volts and stayed there for about 20 minutes. I could not get any amperage measuring devise on those little short wires, but the alternator was warming up also so I am sure it was charging the battery at near maximum output. Just an old battery that would not take a charge, gave the appearance of maybe a charging problem. I am happy with 13.6 volt charge. Also along the way running the engine up to 2,000 for 20 minutes I checked the cooling system with my temp gun. Read 178* at the thermostat housing, so it probably has a 180* thermostat in it. So cooling is probably OK. I am going to look into some beet juice tomorrow.

 

[number two]

The B7800 comes standard with the dynamo with a 13-14 amp output.
An alternator kit is/was available for about $200.
I believe the dynamo produces AC voltage.
Trouble shooting procedures should exist in TBN somewhere.

 

[suntreemcanic]

I do not believe I have a charging problem, it charges at 13.6 volts. The battery was 8 years old, I have found a written record the tractor has run 8 hours in the last 6 years. So just some good exercise is doing wonders in perking her up. I am going to change all the oils and filter when I get my manuals.

 

[rswyan]

The reason I asked about the rpm was I have a B2910 (also with a dynamo) - which is a near twin to your B7800 - and have found that when using a Fimco electric sprayer for spraying for extended periods of time (hours) - at fairly low rpm (1200) - the battery will be severely discharged and would not have enough juice in it to start the tractor if it was turned off immediately.

Difference between a dynamo (generator) and an alternator I believe.

 

[suntreemcanic]

I often plow snow at night because I am busy during the day and I plan installing a couple work lights. I will have to check output of the dynamo. It looks like it would be real easy to install a small single wire Delco alternator.