Battery not charging

I'm not sure what voltage readings on a battery actually tell. The tests I know, at least on alternator charging systems, require a load tester. A load tester places a load on the charging system close to an alternator's rated output and then measures both the alternator voltage and current output under those conditions. A charging system's performance can't really be determined unless the system is under a high load. There are a bunch of tests for both the alternator and regulator if the alternator output tests fail.

However, I'd start by ensuring a good battery and low resistance in the battery terminals and cables. A battery capacity test with a hydrometer should be taken and all battery terminals and cables (including the chassis end of the ground cable) should be inspected and cleaned.

I'm not completely certain yet but a cracked battery cable end and some dirty terminals may be the explanation for a starter problem I have rather than a bad solenoid. It's good practice to clean everything periodically. High resistance in the wiring certainly will keep a battery from charging as will a bad battery. Bad batteries can have good voltage readings.

There should be 14.2 or a little above volts on the battery terminals when charging. If you see less than that, check the voltage on the battery cables. If there is a poor battery connection you will see a higher (or your needed 14.2 volts) on the cables. If there is a difference it is a clear indication that you need to clean the battery connections.

If you have lights or other accessories that can be turned on, do so and see if the alternator/generator still maintains the 14.2 volts charging voltage. If it does that is a pretty good indication that the charging system is doing what it is supposed to do. The only time it might not is if the battery is real low and the alternator is already putting out lots of current trying to charge the battery. Check it again after it has run for awhile to see if the voltage has come up to the required amount.

Of course testing it with a load system is a good thing to do to find out if there any open diodes or other problems that would not allow full output, but most of us don't have access to that equipment.

Checking battery voltage drop during starter engagement can tell a lot too. If the battery voltage dives way down to only a couple of volts it is a good chance you have a bad battery. If the battery voltage holds to around 8 to 10 volts or more when starting, watch the voltage at the starter terminals. If there is a much greater voltage drop at the starter, you may have bad connections at the battery or on one of there other cable connections.

The first thing that should be done if you suspect battery / charging / starting problems is to clean the connections. Remove and clean the battery terminals themselves and the cable terminals. Buy one of those little battery terminal cleaning brushes. Well worth the few bucks they cost. If you don't have one take a knife and scrape the post all the way around until you have shiny lead on the whole surface. Do the same with the cable ends. They must be shiny clean.

The other ends of the battery cables can sometimes be the culprit too. Take them off and scrape / wire brush them shiny clean too. It is amazing how a little corrosion can cause problems. Even though you may have the connection tight, if it is dirty it may not make good connection under high current loads.

On 6 volt systems good connections and proper size cables are even more important than on the 12 volt systems.

Regards
Gary

My only comment is that these checks aren't entirely conclusive and I have found myself testing around in circles. The good thing about the formal procedures with a load tester is that they give a decision-tree that identifies an exact problem quickly--run the first test; if it passes go to the next one; if fails run a different test etc.

The poor man's load tester for cars is just turning on all the accessories, but most tractors only have lighting, which isn't enough of a load.

Tests for my 35W-rated alternator takes a 30A load. The load would be created through about .5 ohm and would generate around 420W. An expensive load tester uses a variable carbon pile. My lights (including aux work lights) give me about half of that. I suppose that using a cigarette lighter car accessory like an air pump would get me into the ballpark. In the past I've thought about rigging up a series parallel network of 110V light bulbs for a load but the resistance of light bulbs changes when they heat up.

Anyway, the load test thing can be done without an expensive shop tester, but of course it would be best if the problem was found with the checks you describe. As we've both said, you have to start by knowing that the battery and wiring are good.