Amp draw on starter is to much? - PeachParts Mercedes-Benz Forum

stephenc03 · #1 05-03-2008, 07:14 PM

I finally tested the starter on my 85 300SD W126. It had over 350 amps when cranking. Does anyone know what the safe amount of draw for these starters are. This seems a little hig considering I tested my amp draw on my 97 dodge 2500 cummind diesel and it was only 250.
-Stephen

babymog · #2 05-03-2008, 09:55 PM

Seems high, looks like time for a starter rebuild.

Although, it is a direct-drive, I believe the cummins is a gear-reduction starter.

stephenc03 · #3 05-03-2008, 10:00 PM

Quote:

Originally Posted by babymog

Seems high, looks like time for a starter rebuild.

Although, it is a direct-drive, I believe the cummins is a gear-reduction starter.

What does that mean direct drive?
-Stephen

babymog · #4 05-03-2008, 10:05 PM

Pinion gear on the end of the armature shaft, no gear reduction.

Mister Byrnzoil · #5 05-03-2008, 10:41 PM

is it having starting problems? That doesn't sound too far out of line... were you testing just the starter or the draw of the starter and glow plugs?

stephenc03 · #6 05-03-2008, 11:15 PM

i tested it with a mechanics tool that measures the amps when it cranks. yes I have had trouble with it starting. within about 2 or three attempts, it will completly drain a charged battery.

Johnt49 · #7 05-04-2008, 10:09 AM

Sounds like your battery might be suspect. To load test a fully charged battery you load it at 1/2 the cold cranking amps rating for 20 seconds. It should not drop below 9 volts. The battery in my car is 1000 cca, yours should be similar. That means it's tested with a 500 amp load. If your fully draining the battery in 3 attempts at 350 amps, it sounds like your battery is weak. A weak battery will cause the amp draw to go up. It will also over heat the starter causing it to fail.
If your battery checks good, the initial draw when you first hit the key should be around 350-400, but this should drop to around 175-200 after engine starts turning. If it remains at 350 that's too much. Your bushings are probably worn causing the armature to drag against the field windings. If your handy with tools the bushings & brushes can be replaced for next to nothing.

stephenc03 · #8 05-04-2008, 10:17 AM

Quote:

Originally Posted by Johnt49

The initial draw when you first hit the key should be around 350-400, but this should drop to around 175-200 after engine starts turning. If it remains at 350 that's too much. Your bushings are probably worn causing the armature to drag against the field windings. If your handy with tools the bushings & brushes can be replaced for next to nothing.

I didn't notice what it dropped down to. However, I do know that it will drain a completely charged battery in a matter of seconds to maybe a minute. I am not cranking for a minute but at most ten seconds rest for 30 seconds a try again. The battery will be dead in a minutes. That would tell me that it has excesive draw?
-Stephen

Johnt49 · #9 05-04-2008, 10:28 AM

Sorry. I was in the middle of editing my post when you replied. Reread it & see if it makes any more sense. I'd hate to see you spend money in the wrong direction before a complete diagnosis.

stephenc03 · #10 05-04-2008, 10:38 AM

Well, i know that the battery is good because it was replaced a month ago. it is the typical cca850 and ca 1000. I did a load test with one of those old school load testers. it held fine. It took me a half an hour to jump start it yesterday. I had my 2500 dodge cummins diesel at 2000 rpm with two batteries and it finally started.
-Stephen

Johnt49 · #11 05-04-2008, 10:59 AM

Quote:

Originally Posted by stephenc03

Well, i know that the battery is good because it was replaced a month ago. it is the typical cca850 and ca 1000. I did a load test with one of those old school load testers. it held fine. It took me a half an hour to jump start it yesterday. I had my 2500 dodge cummins diesel at 2000 rpm with two batteries and it finally started.
-Stephen

New doesn't=good. Babies die! A generic "old school load tester" will not put enough of a load on a battery that size to give you accurate results. Most of them are good for about 200 amps. I'm not saying I'm convinced your barrery is bad, but your numbers are telling me something's not right with the battery, or the amp readings aren't accurate. I just want you to be sure before spending money on the wrong part. You'll still need to repalace the ofending part whether you get it right the first time or not.
I owned an auto electric business for over 20 yrs and somethings not adding up.
To properly test the battery it needs to be fully charged, then let it cool for about 1 hr before load testing.

stephenc03 · #12 05-04-2008, 12:16 PM

The original battery in the car is about a month old and i took a new battery that I bought 2 months ago and stuck it in there as well. I have two identical batteries that have been purchased in the past two months and the car has killed both of them in a matter of minutes. I did charge the donor battery and had the same results; low cranking rpms with 350 amps at initial cranking and it kills the battery way to soon. also i charged the battery with my truck for 15 minutes at 2000rpms my volt meter on my truck was ready well over 15 volts when charging. that isn't enough to charge the battery?
-Stephen

Johnt49 · #13 05-04-2008, 04:11 PM

Sounds like you've eliminated the battery as the problem. Let us know what you find.

Diesel911 · #14 05-04-2008, 05:49 PM

I checked the current draw twice on my so far good running starter with an inductive type amp meter and it had only a little over 100 amps of current draw. This was after cycling the Glow Plugs with a temp of around 76 degrees.

P.E.Haiges · #15 05-04-2008, 10:42 PM

stephen,

More likely a bad armature in the starter than bearings. The armature gets internal shorts and draws a lot of current but doesn't develope enough torque.

Only solution is to replace armature or starter.

P E H