Starter Cable Size

[ArtGill]

I'm changing my NJT model 20 from air start to 12v start.  I have 4/0 cable to run to the starter.  It will take 10 ft of positive to run from battery to master disconnect to starter.  If I go straight from the batteries to the starter it would only be 5 foot.  The ground cable from the starter to the battery grounds will be 5 feet.  Questions:  1.  Is the cable large enough to prevent voltage drop over 10 ft?  2. Should I run the starter through the master disconnect switch?

Thanks,  Art

[Cary and Don]

Our starter cable runs 20 feet and it is 4/0. Our disconnect is right at the battery and the engine starts through it. It is a big manual switch.  There was a medium sized switch on it when we got it and it died.

Don and Cary
1973 05 Eagle
GMC 4107
Neoplan AN340

[Melbo]

4/0 cable is the correct size

The disconnect switch has to be the heavy duty switch like the one that you already should have on your bus.

HTH

Melbo

[JohnEd]

4-0 is the right size and should be sufficient.  Operative word there is "should".  You can tell if it is with a simple test:  Measure the voltage from the lead battery plus terminal to the starter bolt.  Run the starter and the voltage you see is the "LOSS" in you +12 volt cable.  It should be a volt or less.  Do the same to your ground, -12 volt, run.  add the two losses together then subtract that number from your bat voltage, while cranking, and you have some idea of what the starter actually gets to do its job.  The fastest check is to measure between the starter + bolt to the - bolt while cranking.  The mfr calls for 10.5 volts MIN and prolonged cranking at 9 volts will burn it up.  If you only read something below 10.5 you then must determine which run has the loss and which connector in that run is the problem.  Could be the bat term connector or the starter connector term or it might be the wire.  And those problems might be in either the + or - run or BOTH.  There is no compromise on this....you must get the correct voltage.  The battery itself has resistance and a weak battery has more than allowed so getting a reading on the actual bat voltage while cranking is the starting point.  You should establish a base-line for all these readings for future troubleshooting.

HTH,

John

[luvrbus]

Art the Eagle used a Cat style disconnect switch 25 bucks from a Cat dealer you can buy 2 styles with keys or a handle I use the key type inside you can remove the key and it is flush on the out side the handle type.
Still I like the keyed type best the key stays in the unit  only way to  remove the key is in the shutoff position part # 7N0718 from Cat.
Eagle used 1 on each battery the 15 and 20 had 3 group 31's 

good luck 

[rv_safetyman]

I did not realize that the Eagle switch is the same as the CAT.  

I have had to do a bit of work getting ready to do a customer demo this week out in CA.  The unit is a 950H and uses the switch that Clifford mentioned (key style).  The customer wants the power shut down if there is a fire.  I had to look up the capacity of that switch.  It is rated at 125 amps continuous and 1000 amps intermittent.  The demo will have an electric solenoid that is rated at 500 amp continuous and 1500 amp intermittent.  In the actual installation, it will be in series with the Key switch.Big sucker and gets very warm without a special control unit ($205!).  The solenoid is $235.

The  CAT switch is the same as this one:

http://www.britaxae.com.au/am/new_product/ch_disconnect_switch_key.html

Art, since you shut off switch did not have to deal with starting loads, I wonder if it will have enough capacity for your conversion.  My guess is not.  Pretty easy to buy the CAT switch and then you will know that it will work.

A bit a trivia.  I was told that the CAT and similar equipment is required to have a key battery switch by homeland security.  They said that it was to make sure that the equipment was not used to do a ton of damage to structures.  Second bit of trivia:  CAT puts the disconnect on the ground cable.  I think that is a great idea.

Jim

[HB of CJ]

Could you go to 000000 cable?  How much would that $cost?  Does the existing master disconnect switch have enough amperage rating to handle your starter needs?  I was also told that such heavy cable should have a special swagged connection with shrink wrap with no sodder used...just the very heavy swage.

If all of the above are done, then you could use the master disconnect switch between the batteries and starter.  You could even use a little bit more six ott cable to hide the switch somewhere only you know about for more security...like somewhere up hidden by something.  HB of CJ (old coot)

[Len Silva]

The Cole Hersee 75908 is rated at 300/2000 and readily available.  Here is one source:
http://www.ryderfleetproducts.com/ryder/af/ryder/core/content/product/srm/key/V30%2075908/pn/Master-Disconnect-Switch/erm/productDetail.do

[chev49]

course almost equipment uses generic keys which will fit all the others of the same type and/or even the same make... and you can  buy the keys from the dealers....
i have about a dozen keys i keep on a ring for when im working on something and the real key is in the office...

[ArtGill]

Thank you for the replies.  Even with the additional 5 feet of starter 12+ cable, I feel the available ability to disconnect from the starter could be worth while.  I think the disconnect is the same one Eagle used on electric start coaches.  I will check for the voltage drop after completing the install.

Thanks,   Art