Parasitic battery drain

[Denna]

Regarding a 1976 Massey Ferguson 245 Diesel.

After replacing the following with new parts, the battery is constantly drained if the tractor isn't used within 4 days.

Battery
Battery cable to starter
Starter
Alternator

Two electrical items are not currently working.

A wire is connected to the fuel gauge, but is not connected to the fuel pump.

The headlights have never worked.

Any ideas on how to confirm what is draining the battery ?

 

[Dieseltech]

I remove the battery ground cable and put my test light between the cable end and battery post. The light should not come on if everything is OK. If light DOES come on, there's a draw somewhere. Unhook the alternator plug in connector and see if light goes out, if not unhook the large alternator battery post wire too. MF used an excite diode in the wire to the alternator to turn it on, and diode MAY be bad. Could also be the oil pressure switch bad on the back of the oil pressure gauge, MF used it on diesel models instead of using the key switch like gas engines used.

 

[shaeff]

(quoted from post at 17:42:57 05/17/22) I remove the battery ground cable and put my test light between the cable end and battery post. The light should not come on if everything is OK. If light DOES come on, there's a draw somewhere. Unhook the alternator plug in connector and see if light goes out, if not unhook the large alternator battery post wire too. MF used an excite diode in the wire to the alternator to turn it on, and diode MAY be bad. Could also be the oil pressure switch bad on the back of the oil pressure gauge, MF used it on diesel models instead of using the key switch like gas engines used.

All of this. Great post as usual.

For what it's worth, my brand new alternator causes a parasitic drain. I have a quick disconnect on my negative terminal because I didn't feel like going through the hassle of sending it back and waiting forever for a new one.

 

[Denna]

Dieseltech,

Thanks for the help.

If it's the diode, where can you buy a replacement wiring harness between the starter and alternator ?

 

[Caryc]

(quoted from post at 09:43:50 05/23/22) Dieseltech,

Thanks for the help.

If it's the diode, where can you buy a replacement wiring harness between the starter and alternator ?

And if you get tired of going through all that crap, this little gem is worth it's weight in gold.

 

[Jim.ME]

The alternator has internal diodes, that is where the bad diode would be. The diode in the external excitation wire, that is often discussed, would not cause the drain. So the alternator would need repair or replacement.

If you want to use a disconnect switch, Research what you are getting. I would recommend a heavier one to minimize cold start issues. These larger types are used on heavy equipment and can be had with 1000 amp surge ratings.

 

[jvin248]

.

The big cut off switch is a really nice solution ... but it's expensive. $30 for the switch and $30 for the extra battery cable. Then finding a place to mount it and making a big hole in sheet metal.

Or the $6 Harbor Freight 'Green Knob' solution ... however it is a bit long and exposes the lug to shorting against the hood, dash, fuel tank, etc around the battery if not careful during installation.

But disconnecting the battery saves a premature battery replacement cost.

.

 

[J.Wondergem]

(quoted from post at 07:31:39 05/28/22) .

The big cut off switch is a really nice solution ... but it's expensive. $30 for the switch and $30 for the extra battery cable. Then finding a place to mount it and making a big hole in sheet metal.

Or the $6 Harbor Freight 'Green Knob' solution ... however it is a bit long and exposes the lug to shorting against the hood, dash, fuel tank, etc around the battery if not careful during installation.

But disconnecting the battery saves a premature battery replacement cost.

.

Could turn it side ways so it don't hit anything.

 

[Caryc]

(quoted from post at 14:19:06 05/28/22)

(quoted from post at 07:31:39 05/28/22) .

The big cut off switch is a really nice solution ... but it's expensive. $30 for the switch and $30 for the extra battery cable. Then finding a place to mount it and making a big hole in sheet metal.

Or the $6 Harbor Freight 'Green Knob' solution ... however it is a bit long and exposes the lug to shorting against the hood, dash, fuel tank, etc around the battery if not careful during installation.

But disconnecting the battery saves a premature battery replacement cost.

.

Could turn it side ways so it don't hit anything.

Yep been using it for many years. Not one problem or dead battery.

 

[shaeff]

(quoted from post at 08:31:39 05/28/22) .

The big cut off switch is a really nice solution ... but it's expensive. $30 for the switch and $30 for the extra battery cable. Then finding a place to mount it and making a big hole in sheet metal.

Or the $6 Harbor Freight 'Green Knob' solution ... however it is a bit long and exposes the lug to shorting against the hood, dash, fuel tank, etc around the battery if not careful during installation.

But disconnecting the battery saves a premature battery replacement cost.

.

The disconnects go on the negative side, so unless you're positive ground shorting won't really be an issue.

I use the green knob style because it's inexpensive and gets the job done.

 

[J.Wondergem]

I do too and I didn't have a drainage problem to start with. Works good for tractor shows and winter storage.

 

[Denna]

Jim.ME,

Thanks for the help.

The alternator is new from NAPA.

However, this parasitic drain was also occurring with the old alternator.

I thought the old alternator was malfunctioning and not supplying power to the battery. Which is why a new alternator was installed.

 

[Jim.ME]

You haven't said if you have an original three wire or if it has been replaced with a one wire alternator.

Test for the problem or you are just guessing at the cause. You need to follow Dieseltech's suggestion to find the draw. There could be a short somewhere that will get worse over time and could cause a fire. The new alternator could be a drain. Unhooking the battery wire from the alternator (same test for one or three wire ones) is one check to see if that stops a drain. For a three wire alternator, other possibilities are the oil pressure switch that controls the charging and gauges (located behind the oil pressure gauge) has failed closed and is supplying power to the alternator excitation (#1) terminal all the time. Or if someone did some rewiring, bypassed the oil pressure switch and just hooked the excitation wire to a constant live power, source it would cause a drain. Use a test light to check the excitation wire at the alternator to see if it is dead when the engine is stopped. (I believe you diesel uses a pull to shut off cable so the problem of not being able to shut the engine off [if a diode is not used in the excitation wire] due to back feed from the alternator on gasoline or electric shutoff injection pumps, would not occur.)

If it's not in the alternator, or other electrical component you can isolate, you will need to move harness wires and search for worn and chaffed areas.

I will highly suggest unhooking the battery or adding a disconnect, of your choice, until it is found and repaired.

This post was edited by Jim.ME on 06/01/2022 at 03:36 am.