'71 RL700L charging issues

[Tomb8764]

Long story short, my truck charges fine on the right bank of batteries (2 6 volt).   But the left bank (2 6 volt) only maintains at 12 volts, never reads anything higher than that when running.  I do have to jump the left side from time to time to get started. Also a bonus, whenever you run any accessories, such as headlights or heater, you get a voltage drop on the left bank.   The right bank stays fine and always charges as it should.   Any thoughts?  

[doubleclutchinweasel]

Bad batteries on one side?  Bad crossover cables?

[Joey Mack]

I'm guessing it's a 24 volt system with negative ground?  I would just check the battery cables for proper routing, and tightly crimped ends. D.C.W. has a good point as well...  I assume the 2 6 you post is 26 volts when running...  it should be 28.4 ish when running...  any thoughts?  jojo

[Tomb8764]

Thanks for the input guys.   Batteries are all good, the 2 that dont seem to charge were new last summer.   I'll definitely check the crossover cables.  Honestly I'm not sure if the truck is 12v or 24v.   All the lights seem to be 12v.    I've got someplace to start, thanks!

[Tomb8764]

Also I'm pretty sure the truck is positive ground.   I'll double check that information in the daylight tomorrow. 

[Hayseed]

10 hours ago, Joey Mack said:

  I assume the 2 6 you post is 26 volts when running

I think he means 2 6volt batteries.. But I have been wrong before (Just ask My Wife)

[mowerman]

Faulty parallel switch????! Sounds like an easy fix with a test light good luck.. Bob

[mowerman]

Nice lookin ride.. Bob

[h67st]

4 hours ago, mowerman said:

Faulty parallel switch????! Sounds like an easy fix with a test light good luck.. Bob

I'm with Bob on that...if it's got a S/P switch, could be the problem.

[Joey Mack]

Hayseed, I laugh... If you ask my wife, a broken clock is right more times a day than I am..     (2) 6volt batteries makes sense to me..  jojo

Edited February 24, 2022 by Joey Mack
More content needed

[tjc transport]

22 hours ago, mowerman said:

Faulty parallel switch????! Sounds like an easy fix with a test light good luck.. Bob

i agree with Bob. sounds like a faulty switch, or a bad cable going to the left side batteries.. if i remember correctly, you should have 12 volt electrical system with 24 volt start and positive grounds. 

this system uses all 12 volts parts EXCEPT for starter and batteries.

the 2 6 volt batteries on each side should be hooked series for 12 volts, and then connect parallel to the other side to start. but when running and charging, the two sides are connected in series for 12 volts to each side.

[Joey Mack]

Yeah.... What he said.....    

[tjc transport]

you actually understood that???  😲

[Joey Mack]

I did, however when you first said to parralel them I believe you meant 'series' because thats how you double the voltage.  it would make 12 v on each side, then for the starter you would series those cables. and for the cab power you would come off one set at 12 volts...  Good chance I F'd this up now...  jojo

[mechohaulic]

all right answers ; just said in different ways. two 6's per box cabled together in series  + of one to - of other equals a X factor= 6x2=12volts per box.purpose of series parallel  switch  take the four  big sixes(12volts each per set) put the two sets in SERIES making it 24 volts to starter ONLY. the unit should be 12 volt positive ground. does it have a generator or alternator??? one set when a S/P switch involved always gets less charge not that noticeable like your though.   with all the new stuff today 12 volt start . batteries parallel to each other + to+ to + can go on endless no matter how many connected its still same voltage. 

[mechohaulic]

back to original situation, i would consider a faulty S/P if all cables are ok. NO  S/p switch just two sets of batteries; a connection seems likely. a cable ::1 would still carry voltage; 2 - putting a charger on it  shouldn't make a difference  having a bad cable . power can go from charger to starter, should go from generator/alternator to battery set .   was a voltage check done at both battery boxes AND off the gen/alt output. 

[mechohaulic]

don't remember for sure ,  i think on those "new trucks"LOL  ground  cables go from batteries to frame rail. at engine area short cable goes from frame to  starter.  not like older units that ran a cable  entire length from  batteries to S/P switch. corroded cable end behind battery box usually first place to check. enough of  connection  from frame and cable too get very little voltage    possible

[tjc transport]

12 hours ago, Joey Mack said:

I did, however when you first said to parralel them I believe you meant 'series' because thats how you double the voltage.  it would make 12 v on each side, then for the starter you would series those cables. and for the cab power you would come off one set at 12 volts...  Good chance I F'd this up now...  jojo

nope, you got it rite. and i fixed the typo too.  👍

[h67st]

14 hours ago, tjc transport said:

you actually understood that???  😲

I did right up until he mentioned the flux capacitor.

[Joey Mack]

I would like to be educated on the S/P switch, not sure if I know what it is... jojo

[Joey Mack]

O'Rielly's sells flux capacitors ...  

Flux Capacitor

Part # 121g Line: EB

This item is not available for purchase.

[doubleclutchinweasel]

Didn't all the 24V starting system trucks use the manual push button to activate the series starting circuit?  Seems like all the ones I saw did.  Turn on the key then push the button.  All the 12V starting systems I ever saw just started with the key.

Maybe that's a way to tell if it has a 12V or 24V starting system.

If it IS a 24V start, then that unit would definitely be a good place to start.

Edited February 25, 2022 by doubleclutchinweasel

[mechohaulic]

1 hour ago, Joey Mack said:

I would like to be educated on the S/P switch, not sure if I know what it is... jojo

a series parallel switch is (WAS) the big bulky switch located between seats in cab under a metal box (B-models). later units had some mounted in battery box. ALL the battery cables went to the S/P switch. key on- push button; power (12 volts) went to the S/P, internally the switch took the two sets of 12 volt batteries connected them in SERIEs ---- 2x12 = 24 volts to starter. truck starts ; coil in the S/p clicks off unit is a 12 volt with 24 volt starter. the S/P was basically the same as soliniod  on a starter. large power to it , small power source to click it on. like the use of 55 rears many things in the good days were "over kill". todays electronic world  it only takes 2 0r 3 batteries in PARALLE  to start things. 

[doubleclutchinweasel]

The old R600 I drove back then had the 24V start.  Pushbutton to engage the S/P switch was on the dash.  Seems like the key was on the left side and the pushbutton was on the right side of the steering column.

The one I had more recently was all 12V.  So, it did not have the S/P switch or the pushbutton.

[mechohaulic]

41 minutes ago, doubleclutchinweasel said:

Didn't all the 24V starting system trucks use the manual push button to activate the series starting circuit?  Seems like all the ones I saw did.  Turn on the key then push the button.  All the 12V starting systems I ever saw just started with the key.

Maybe that's a way to tell if it has a 12V or 24V starting system.

If it IS a 24V start, then that unit would definitely be a good place to start.

I never gave that a thought . All the older series =B's, L's, some very early R's etc had button start. another factor is in the day a key was on/off ONLY. no acc position. key was one wire in one out.  newer key switches gave the acc position  no need for button start . B's didn't need acc position to turn on the AC !

[tjc transport]

3 hours ago, Joey Mack said:

I would like to be educated on the S/P switch, not sure if I know what it is... jojo

no you don't... believe me. they are/were a royal pain in the asterisk. 

when we had problems with them, we ripped them out and put 12 volt starters in.

2 hours ago, doubleclutchinweasel said:

Didn't all the 24V starting system trucks use the manual push button to activate the series starting circuit?  Seems like all the ones I saw did.  Turn on the key then push the button.  All the 12V starting systems I ever saw just started with the key.

Maybe that's a way to tell if it has a 12V or 24V starting system.

If it IS a 24V start, then that unit would definitely be a good place to start.

we only had one 12/24 truck with pushbutton. the other 9 12/24 volt positive ground trucks were all key start. 

but then again, those 9 trucks were all custom built/ordered new.