Im trying to sort out a starting problem that I have lived with for a couple of years.
I replaced the 2 8D batteries in my GMPD4106 with 3 group 65 batties and relocated the battery compartment closer to the engine. However the bus does not want to start when the engine is warm.
I understand that an 8D has 1375 ca and the group 65 has 950ca. I was previously told that hooking up the batteries in parallel does NOT give you more ca but rather more capacity. So , in my way of thinking then one 8D gives you 1375 ca for a certain period of time and 2 doubles the time. Is that correct?
My orignal thought was that 2 8D would give you a total of 2750ca and 3 group 65's gives 2850.Apparently thats not the case and in effect I was going from 1375 to 950ca which would expalin my problem. Therefor even adding a 4th group 65 would not give you more CA.
Regards
Fred Mc.
Not sure what your getting at, but the higher the resistance the more amperage that is required to do the job it used to do...
The hotter something gets the more amperage it needs also...as heat is resistance also...
Have you ever had the starter tested ? replaced ?
The solenoid contacts inspected ? replaced ?
Cables internally (not visibly) corroded ?
If you connect similar batteries in parallel then yes the cca of the batteries is combined. If they are connected in series (2 12v batteries connected to provide 24v) then the cca remains the same, only the voltage increases. The difference between lets say two 1100 cca group 31 and two 1100cca 8d batteries would be the reserve capacity, or the length of time the batteries can provide the cranking power. I just used 1100cca as a figure for comparison to show that all batteries of the same cca are not equal in performance.
You may want to check the starter after having the batteries load tested. 8v-71's start almost before you hit the button.(at least with 24 volt)
When cold it starts within a few revolutions but once it warms up its lucky to get one revolution.When it cools down (hour or so) its fine again. Starter was new a fe years ago as were cables with very little use since. Also cables go directly to the starter.
Quote from: Fred Mc on September 07, 2015, 06:11:53 PM
When cold it starts within a few revolutions but once it warms up its lucky to get one revolution.When it cools down (hour or so) its fine again. ...
Do you mean when it's warm, the starter only turns over one revolution then bogs down and won't turn the engine over any more? If so, that's strange.
In the starter world that is called "heat soak" maybe it needs a heat shield,too bad they don't make 39MT starter for you lefty's that would solve your problems
Quote from: luvrbus on September 07, 2015, 06:27:15 PM
In the starter world that is called "heat soak" maybe it needs a heat shield
I guess that's possible, I've just never seen one on a Detroit.
I have seen them on GM buses before the starter is real close to the manifold it's not like the average DD down by the oil pan
when your starting it, use a volt meter and check the volts at the starter solenoid, going in and coming out. should be the same on volts both sides. if the volts instantly fall off, means loose connection. check the start signal wire as well. feel the cables at the clamps and ends for getting hot. if hot at clamp or end, then loose or bad end. clamps get bad connections inside where the cable goes in some times. if the clamp gets hot while running the first time from cold its loose. gounds as well. if the cable gets hot during cranking the its too small. bad crimps are common on home made cables. those batteries are more than enough to crank even a frozen 8v71. i did my 5 with 2 65s backed by a smaller chevy side post battery each and works great. check with a torque wrench how much torque you need to turn the crank shaft cold verses warm. maybe getting tighter when warm.probably not.
We picked up a couple used 4D batteries to start our Neoplan to keep the engine alive in. They crank that 8v92 just fine. They are a lot easier to handle than the 8Ds and seem to work just as well for starting.
Don and Cary
Be careful lifting those 8D and 4D batteries. My back is sore now after lifting 105 pound batteries into the bus with a friend a week ago. The original batteries we took out were about 95 pounds and didn't seem nearly so heavy.
Check the terminals on the starter for tightness. My ground cable was loose-started fine when cold, but missed many times then sometimes would start when hot. After tightening the terminals, everything is fine.
Electricity is simple mathematics. If you have one 1000cca battery and add a second 1000cca, then you have 2000cca-if only you have enough cables to carry the load. I switched my 8V-71 from 2-8D to 2-31. Turns the engine over fine, cold, hot, etc. If I need more juice, I have a jumper solenoid that I can tap into my 2-8D AGM Lifelines. Good Luck, TomC
All starters have a max CCA the first 2 batteries in a string when parallel are the CCA you add as many as want say if you had 4 1000 CCA batteries the way it is explain here that would be 4000 CCA that would fry a 42MT starter with a max of 2500 CCA the second you tried to start a engine.
That why Delco and others use a over crank protection OCP device on starters to prevent that anything over 2500 CCA it breaks the circuit then resets after cool down some of the new model starters can go to 3000 CCA
You say you replaced the cables. What gauge are the new ones?
Virtually all new big rig trucks use 12v starters. At Freightliner (and I assume most others too) when you specify a sleeper cab, you automatically get a 4 battery system. The standard batteries are 950cca, which works out to be 3800cca. But-they are wired with two cables from the starter with each cable servicing two batteries in line. So wiring wise, that would give an effective 1900cca with twice the reserve capacity. Main reason for 4 batteries on the sleepers is to allow the drivers to run their TV's and computers. The sleeper trucks also have a 12.3v cut out for the cab. But, you leave the headlights on, you can still run down the batteries.
On my old ('85) Kenworth, I have a jumper solenoid so I can run 12v system but with a 24v starter. I run 4-1100cca batteries. Needless to say, the big Caterpiller (14.6 liter) 3406B turns over easily. Good Luck, TomC