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On 9/21/2024 at 1:16 PM, Geoff Weeks said:

There are 3 ways to eliminate the Series/Parallel switch, or there used to be, one may not be available due to Elon buying then re selling Maxwell.

1st is to change the starter and cabling to a 12 volt crank/ run system

2nd is to used a TR alternator with both 12 and 24 volt output, The batteries are wired in series and the 12 volt truck loads are placed on only 2 of the batterys, the remaining two go to the starter in series with the 1 st two. Works but the batteries should be swapped around periodically for best life.

3rd and the one I would recommend, if it is still available is the Maxwell EMS, it will charge on 12 volt but supply 24 volt to the starter. It is the size of one Group 31 and can supply more than 4 group 31's can for short cranking loads.

 I had the 12 volt version in one of my trucks that didn't have room for air start. Even with the 12 volt holding less power than the 24 it cranked no problem in -25F temps.

 The 24 volt unit would charge on anywhere from 10 volt to 30 volts, so ideal for a 12 volt run truck with a 24 volt cranking system

I can honestly say I've never seen batteries like those before. The one on the left, that's wild how the fill ports are angled and caps are tied together.

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32 minutes ago, h67st said:

I can honestly say I've never seen batteries like those before. The one on the left, that's wild how the fill ports are angled and caps are tied together.

Those were industrial " floor scrubber" deep cycle batteries, a smidge wider and longer and about an inch taller than a Group 31. IIRC 155 amp/hr a piece

 I found in the end, that I didn't need the extra power and went with Gp 31 deep cycles later. IIRC 135 amp/hr.

 On two of my trucks, I had air start and four deep cycles, that truck was shorter and didn't have the space for a conventional air start tank, and the old "hot dog" vertical tanks CF used to use are hard to find, and when you do, are so old as to be not serviceable. That truck got 3 of the floor scrubber batteries and the Maxwell, which is much like an electrical version of air start, lots of cranking power for a short duration.
 

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1 hour ago, mowerman said:

I only owned one truck with the 24 V starter and it was too long ago, but it did have 4—6 V batteries of parallel switch but yeah that would make sense. I guess even today four six volts would give you a lot more cranking power than two 12s… bob

Back in the day, the only battery with enough CCA's to crank a diesel were large 6 volts, with around 900-1000 cca's

 It takes around 1800 to crank cold on a 12 volt system and 1/2 that on a 24 volt.

The main issue with 4 6 volts in series, is one weak or dead battery kills the crank. 

 When high output (Gr 31) 12 volts came out, the need for large 6 volts went away.  2 groups of two 12 volts on a 24 volt crank, makes a very powerful system

 2 group 31's is about the minimum to crank a truck engine, either in series for 24 or in parallel for 12. Most modern trucks have a minimum of 3 for a 12 volt and many opt for 4.

 For all out power and almost maintance-free, air start is hard to beat. The Maxwell come a close second, and has one advantage over the air start. If it doesn't start in 30 or more sec of cranking, it will recharge from the "house batteries" in about 10 mins as long as those batteries can provide around 18 amps without dipping below 10 volts. That isn't a hard ask of any single battery!

 The draw back of the Maxwell, and the only thing keeping it from beating air start, is all the power passes through the two 3/8" stud connections, If they become loose or dirty, the connection can arc and weld itself. Keeping them clean and tight especially with the heavy  (000 ga) cable is something that needs to be checked every few months. Going with the 24 volt version would help alot, as the cables could be much thinner.

Edited by Geoff Weeks
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Thanks for all that. I think that was the problem I had I couldn’t get mine running not enough cranking power but I think I had mismatched batteries. I just decided to get rid of it all and put the air starter in. I’ll tell you what that starter was not cheap. I think I paid it thousand dollars 30 years ago exchange but yes after all these years that thing  hold air forever. 

As you mentioned, it’s pretty much trouble free there’s not a whole lot that can go sour and yes, I remember those vertical air tanks. I got mine off an old freight truck T100 Kenworth. In fact they wound up going to work for the same company a few years later used to be Viking freight lines Now it’s Fedex freight Oh hell, I think we’re stepping all over this guy‘s tread now perhaps got him talked into air starter ha ha.. bob

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