Battery/Starter question

A friend of mine has a 40 John Deere and called me to look at it with him today. Has a 1 year old 6vdc battery and when I put the meter on it it reads 6.2 volts but when he tries to start it the battery drops to 2.7. He had the battery tested, tested good, brought it home, ran the tractor twice then this again. In my mind
the battery should hold the voltage if its a starter problem. The starter doesnt get hot or anything. Whats the thoughts out in tractor land, I am kind of puzzled on this one. Thanks

Here is just my thoughts: You say he has a 6 volt battery. Started it up ran it for two times. Now I want to
ask. Have you ever thought of taking the voltage off the generator while the engine is running. what I am
thinking here is like maybe the generator Or the voltage regulator could not be charging up the battery. the
starter might be the problem Is the starter old? When they start to go they require more voltage to make them
work.

Thanks for the reply Brent. I just got involved today so never had a chance to see what the generators was putting out. Starter looks original , but don't know the full history either. I just have never seen a battery drop Vots like that.

A carbon pile battery tester will tell the right story. When you can see the amp draw
and at the same time read the voltage, it takes out the guesswork.

I have a 1951 Farmall M over here at this house that took all lot to start it up. I had to change the
generator and the voltage regulator over to 12 volts and put a 12 volt battery in. Because the engine had
high pressure piston put in when over it was a rebuild.

It's near impossible to get a good voltage reading while cranking. The voltage will drop as the engine comes up on compression, go back up between compression strokes.

Start with a fully charged battery. It should read 6.2-6.4v off the charger.

Get the tractor running, check the revved up charging voltage across the battery. It should be 7-8v.

What size battery cables does it have? It needs size 0 or 00 to operate correctly. Every connection needs to be perfect for a 6v system to work.

If everything checks out, no hot connections when cranking, the generator is working, take a look at the starter. Typically if the starter is trying but can't, and it's worse when the engine is up to temperature, it's only worn bushings. Easy fix.

(quoted from post at 19:39:44 08/11/20) A carbon pile battery tester will tell the right story. When you can see the amp draw
and at the same time read the voltage, it takes out the guesswork.

Click to expand...

+1

it all depends who tested that battery. it can show over 6 volts and be no good. you need to load test the battery first thing to see if it
the battery or starter or engine at fault.

I agree with Steve, if all the battery connections are clean, the battery is charged, and it drops that much I would say the battery is bad.
Check the cranking voltage at the battery, and again at the starter, you may have a bad connection that is not visible.

Henry, a full charged lead acid 6 volt battery AT REST AND STABILIZED should read close to 6.3 volts. HOWEVER A real test which many
sellers offer for free IS A LOAD TEST I suggest that be performed ASAP.

Next if a battery tests okay under load and is full charged, while subject to starter draw and battery condition and capacity, I might
expect it to drop to as ow as even 4.5 volts BUT NOT 3 VOLTS. NOTE if the starter switch or solenoid is bad/resistive (seen that often) it
can drop voltage leaving low voltage on the starter motor itself. Those contacts can bet burned and pitted and resistive and corroded
causing voltage drop across them EVEN IF THE BATTERY AND STARTER IS GOOD A BAD SWITCH CAN CAUSE THE PROBLEM !!!!!!!!!!!

If coupled to a good working charging system subject to battery and RPM at fast RPM Id expect the battery voltage to rise to at least 6.5
volts up to near 7

If voltage is actually dropping that low AT THE STARTER there's excess current flow and the starter motor itself could be the problem.

HOWEVER there can be many causes of excess voltage drop such that voltage remaining at the starter is so low such as

Bad/loose/resistive cables or cable connections or terminals
Too small battery cables
Bad resisitve ground connections
Faulty voltage dropping mechanical push starter switch or electric solenoid starter switch

I suggest A good battery load test,,,,,,,,,,,Check each and every battery and starter and ground cable connection for rust or corrosion or
evidence of heat,,,,,,,Check for voltage drop ACROSS THE STARTER SWITCH OR SOLENOID,,,,,,,,,,Use at least 1 Gauge or even 0 or 00 gauge
starter and ground cables can help

If you can measure the voltage drop ACROSS THE SWITCH/SOLENOID or voltage on the starter input post and voltage on the switches BAT Input
that can find a switch problem

John T

Had a similar thing happen with my diesel 3020. No start, jumped left side battery and it started (24 volt system). Load tested battery, showed 12.7 before load test, went to 4 volts at 100 amps of load and returned to 12.7 after load removed. Replaced battery and it starts perfect. I believe your battery is bad. I don't spend a lot of time messing with a battery that acts odd as I had one that was performing oddly explode during testing. Makes quite an impression. That particular battery was a side post with a crack in the lead strap going to the connection.

I buy my batteries from my local independent auto parts store. Whenever I am suspicious of a battery I take it in and they hook a tester to it which will measure the actual CCA

Thanks everyone for the replies. He did have the battery load tested and they say the battery is good. He brought it home and put it in and it would start twice, the next day it would not. The cables and everything are what has been on the tractor, the ends look good, the starter does not get warm. He has a "smart" battery charger and it says "bad battery" I suggested to him to take the battery to a different source and have it load tested. If they say its good then maybe the starter, which has a mechanical switch attached to it. This little guy is all painted up and I don't want to be the person to chip the paint so he may take it to the local mechanic if the battery tests good. I will update on what is found.

Batteries don't test just good and bad. They should tell you the CCA capability which you then compare to original. More so than if the starter heats up what you want to find out is if any of the cable connections heat up. If you find one that heats up during cranking you have found one that has poor conductivity. It can "look good" but be bad.