I was having a starting problem on my GMPD4106 that I traced to a bad ground at the battery disconnect.
The disconnect is a Blue Sea Systems unit with the following specs.
32VoltsDC
350 Amps continuous
600 Amp intermittant
700 Amps Cranking
1600 Amps Inrush.
I have this on the negative cable going to the starter thru a junction bolt in the body of the bus. The disconnect is connected to the junction bolt via a copper strap. Both positive and negative cables go directly to the starter (as stated the negative cable thru the junction connection)
Is this disconnect large enough for my setup. I have 3 group 31 batteries in parallel.
thanks
Fred
What size starter cables do you have? How are their lugs attached? How long are they? What engine do you have? I'm thinking the Blue Sea switch is probably adequate, provided it has suitable cables (and lugs) between the batteries and starter. If the cables are less than 4/0, if their lugs are hammer-crimped or just badly attached, if the lugs are corroded internally where the cables enter, if the outsides of the lugs are corroded where they make contact, if the cables are just too long, these could be reasons for poor starting. Obviously the starter itself could also be failing, but I would look at the cables first.
John
i would consider everything john said but would also look at the contacts inside the switch...
An easy way to tell if the switch is the problem is to move the cable going into the switch to the junction bolt which will bypass the switch. If the starting problem goes away, then the switch is the problem, otherwise check the cables/lugs/connections. If they are corroded or have an otherwise bad connection, they will heat up after you crank for a while and you can feel which connection is warm/hot. Careful, sometimes they can be very hot!! -Steve
The cables are the same size as the original cables (1/0, i think) but were custom built and machine crimped and go directly to the starter(about 3 ft long).They are attached with 9/16 nuts at the batteries and disconnect. The engine is an 8/71. I took the disconnect apart and there is no apparent burning or arcing inside. I also bypassed the disconnect and went directly from battery to starter and it did start better.Howver, I dont want to eliminate the disconnect due to phantom draw on the batterys . Im going to eliminate the copper strap and junction bolt and see if I can go directly from disconnect to the starter with the cable. The less connections the better, I think.
Regards
Fred.
Quote from: Fred Mc on October 02, 2015, 10:21:45 AM
The cables are the same size as the original cables (1/0, i think) but were custom built and machine crimped and go directly to the starter(about 3 ft long).They are attached with 9/16 nuts at the batteries and disconnect. The engine is an 8/71. I took the disconnect apart and there is no apparent burning or arcing inside. I also bypassed the disconnect and went directly from battery to starter and it did start better.Howver, I dont want to eliminate the disconnect due to phantom draw on the batterys . Im going to eliminate the copper strap and junction bolt and see if I can go directly from disconnect to the starter with the cable. The less connections the better, I think.
Regards
Fred.
If they are 1/0 cables, I think they're too small. As a general rule, starters on buses should always use 4/0 cables, the fattest ones generally available (they're about 3/4" to 7/8" diameter). A 42MT starter is rated at up to 10.5 HP, so it can potentially draw many hundreds of amps. Most Group 31 batteries have 3/8" threaded terminals and starters usually have 1/2" studs, so cables need to be made with the right size lugs on each end. It's also a good idea to use tinned lugs because they corrode less quickly, especially in the presence of battery fumes and road dirt. Whatever lugs you use, have them crimped on with a good circumferential crimper such as the FTZ 94284 that squeezes the lug all the way around to produce a "gas-tight" cold-welded fusion of the cable strands to the lug - a lug crimped this way will appear to be a solid mass of copper if cut apart, with no individual strands discernible. Good heat-shrink should be used to prevent any moisture getting to the joint. If you do all this, whatever starting problems you may still have won't be the fault of the cables!
John
I would think that a disconnect should be on the hot side, not the ground
If you are looking for a high resistance connection or undersized cables use your IR thermometer to check the temperatures.
The factory hot cable to the starter on a 4106 is 4/0.
I fought a starter issue on my bus for a few years. I had the starter rebuilt several time. I replaced all the ground cables. I added a 4/0 ground cable from the engine to the batteries. I replaced the hot 4/0 cable with a new one. In the end I finally found a shop that actually knew how to test and rebuild a 42MT. Both starters (the one on the engine and a spare) I had rebuilt a couple times each had bad windings. Too much was leaking to the housing, lowering the amperage to spin the starter. I even replaced my 8Ds thinking they were the problem! With the properly rebuilt starter, I'm amazed at the speed the engine cranks at now.