Md5a wonbt start with alternator connected

"I have a recently acquired md

"I have a recently acquired md5a- equipped Chrysler 26. It has a 66 amp Delco 3 wire alt. The problem is it won't start with the alternator belt on. When I re-wired the boat 4 mos. ago I wired a relay in to isolate the field wire to eliminate parasitic drag from the alternator while cranking. At the time it worked fine but now when I want to use it it won't start with the belt on! Even removing the relay to isolate the field wire won't allow it to start. I'm guessing the alt. is producing power even though the field wire isn't connected. I did manage to start it with a very loose belt and then tensioned it with the engine running- something that could easily cost me some flesh! Any thoughts? Maybe the starter motor is marginal, but that doesn't explain the loading from the alt."

"Gday Lamont,
A md5a

"Gday Lamont,
A md5a can be hard to start unless every thing is up to scratch at the best of times.I regulary service one that has a bosch 60 fitted starts no problems. My starting procedure on that engine is wot [neutral] decompress untill max rpm drop lever and stand back.Other suggestions are 1.check batt condition & volts + sg.

2.check alt turning resistance by hand.
3.check voltage at starter powered up
4. starter condition ?
5.doe's the engine normally start promptly ? if not you have no show. Cheers Shakey."

"Hi Shakey,
Thanks for the re

"Hi Shakey,
Thanks for the reply. Here are answers to your points:
1.new batt. 12.8 volts
2.new alt. just normal new bearing resistance
3.full voltage right to starter (tried measuring while cranking and got ~11.8-not easy to do with motor jumping around!)
4.sent starter to dealer today. While cranking with decompressor on I notice the speed slow then pick up several times. It also seems to spin at about the same speed (approx.) under compression or not.
5.with the belt removed the engine starts in about 3-4 secs. cold or warm every time. I was quite pleased with the ease with which it started (without alt. of course!)

I'm guessing that the starter is weak and that the alt. is actually energizing and producing power when cranking, which it must be, wouldn't you think? The alt. has the small automotive pulley so the ratio is 5:1 (5x crank speed)

Thanks, Lamont"

"The alternator 'load'

"The alternator 'load' has no influence during cranking.
If you still have the charge light connected, just monitor it. If light stays on, no charging (load) from alternator, just the extra load from pulling it by the belt."

"I would think that the fact i

"I would think that the fact it starts with the alt. disconnected says that the alt. is a considerable source of drag. The charge light goes out when cranking, but it goes out because of the relay I've installed to open the field (charging light) circuit when cranking. That's why I don't understand why the alt. is energizing and causing this drag.
I rewired the engine and control panel in the spring and it worked fine then but I didn't try it again until last weekend."

"'In the Balmar Alternator

"'In the Balmar Alternator Output diagram below, the power output curves are shown 65 amp and 85 amp alternator. Note that the 65 amp alternator in this example, produces more current output (power) at a lower RPM that does the larger alternator until approximately 3300 RPM. Also note the difference that the crankshaft pulley size makes. A larger crankshaft pulley will create a higher alternator RPM; thus, causing the alternator to produce more power at a lower engine RPM. An alternation require one horsepower on a diesel engine to produce 20 to 25 amps and for gas engine 10 to 15 amps.'



You will need to crank your engine up to about 3-500 rpm before the alternator starts delivering. Your MD5 should start long before that!!!"

"If you are not sure if the al

"If you are not sure if the alternator is producing while you have the field coil switched off, measure the battery voltage with engine off and monitor as you atart up. It should go down as engine is cranking under load then go up after engine starts when there is no longer a cranking load and then again more as the alt kicks in. Some alt don't kick in right away allowing the engine to start easier. If the field coil is off the alt will not produce power. If your alt is producing power, then your switch must be on or shorted or there is another path to the field coil from the starting circuit."

"The alternator must be energi

"The alternator must be energized as that seems to be the only reason for not starting when it's connected. The difference in cranking speed when the belt is on vs. off is barely perceptable to me, but not once has it started with the belt on.

When I first tried to start it on Sunday I released the key from the cranking position after 2 sec. because I could feel it fire and thought it was on its way. My son did the same thing the next day thinking it had caught right away.

I keep feeling I'm forgetting something, but can't think what it would be. I stated earlier that it started in May with the field circuit cut-out relay in place, but in thinking back I may have put the relay in after running it and actually not tried starting it after. Unfortunately I've sent the starter away and can't try it with the relay removed until I get it back.

thanks for your comments"

"No offense, but "Must be&

"No offense, but "Must be" doesn't work while troubleshooting. Find the real answer. If your field coil is disconnected by switch or other wise, the alt will not energise. If it is energised, then there is another problem as yet not mentioned by you and that is a short somewhere in the electrical system. Address that issue and your other problem may fix itself or give you a new symptom. Unrelated issues don't usually happen at coincidentally exactly the same time. They are usually related"

"I'll take the alt. to a s

"I'll take the alt. to a shop tomorrow and have them test it, perhaps it's a problem.
From info I've found it is a Delco series 12, but it doesn't have the plastic fan. Instead it has the fan found on the series 10.
It seems that the 3 wire Delco will self energize without the field wire connected, but revs have to be quite high. Of course, an internal short to Bat. could energize the field coil . . ? ?"

I'm wondering why you felt

I'm wondering why you felt it necessary to rewire the alternator circuit in the first place. Was there a starting problem you were trying to address?

"I used to re-fit all Volvos,

"I used to re-fit all Volvos, both diesels and gas engines with the Valeo Motorola 75Amp alternators.
A straight hook up to existing wires, and never anything like this!
I think you are looking in the wrong end of the horse.
The only trouble with the MD5 after such a modification, it was not much power left for the propulsion when alternator was fully loaded!"

"I bought the boat last winter

"I bought the boat last winter in a rather neglected cond. The alt. was there but not wired in and the ign. switch was a mess.
The reason for wiring in the cut-out relay was to eliminate (I thought) any drag from the alt. when cranking.
This engine, apart from this alt. problem, starts easily, within 4 sec."