24v/12v food for thought. Might it work?

[Kodiakkris400]

In my quest for infinate wisdom and to boggle the minds of the thinkers an idea popped into my head. Ultimately I was thinking of how to hook up 12v Accessories to our 24v systems as simply as possible. I have a strong grasp of parallel and series wiring for raising amps and volts, and also understand it can be detrimental to only draw off one battery in a 24v series to get your 12v. So here goes my food for thought(hopefully I can explain this correctly)... What if (leaving the batteries hooked up in their current 24v series) you also grabbed the positive of each battery, and the negative, and made a parallel circut also. This in theory would draw the same off each battery eliminating the undercharged/overcharged situation while providing the factory 24v to the truck, and giving you 12v for accessories. Hopefully an electrical engineer can chime in and shine some light my way, in somewhat lamens terms

 

[m16ty]

You would have a dead short. You can't get past the fact that the positive and negative of both batteries are connected to each other in 24v series.

When you tie both negatives together in your parallel connection, you'll be shorting out the second battery.

 

[emr]

Its not detrimental to hook up off one batt, unless u are trying to pull long periods with no truck running, The situation is no batts charge equally in a 24 volt system as they are designed anyway, the primary battery is always fully charged while the others , Let use the filling the pool as the example,... Here is why ... These are not smart chargers, THERE ARE smart chargers that send algorithms that will fully charge batts down the line, We don't have them in our trucks )) Filling the pool is what happens to our batts , As the first batt fills up the charger has been charging the other in series or parallel .. Pouroing over the sides so to speak ) ... And the last batt will fill to a point to offer enough resistance for the charging system to stop so it does not over charge the first batt, the result is simple . The last batts sulphate more from not ever being fully charged and have a shorter life than the first in line for charging, This is not an opinion )) ALL batts should be pulled cleaned fully charged and rotated at least once a year, THAT will give the true ultimate life of batts, So getting back to pulling off the first batt, It will charge fully all the time anyway. ))) Hope this helps, And its very very true. ))

 

[Kodiakkris400]

Completely overlooked the dead short situation , and thanks for the analogy emr, but since we're on the topic of 12v accessories, I was looking to hook up a stereo (biggest draw with possibly a small, maybe 20amp amplifier), cb, and possibly other small draw accessories. Should I split the accessories between the two 24v banks?

 

[tim292stro]

I concur with m16ty - you're making two lead-acid explosives with a dead short if you wire it your proposed way.

In my mind there are really four "good" ways to do this 12V load from a 24v system all include 2x 12V batteries in series, or a dedicated 24V and 12V battery pack.

1. The CUVC way, one dedicated Alternator for each battery,
2. The mass-transit way, a battery vanner which discharges the high-side battery as much as the low-side battery with a single 24V alternator,
3. The "other" way, a 24V-to-12V step down regulator and a single 24V alternator
4. Separate 12V and 24V systems, separate alternators, a relay to tie one system's ignition control into the other's.

Of the "less than good" variety, I think I recall a charging system from a 1980' vintage Class 8 truck and some diesel Toyota Land Cruisers where the batteries could be either series (24V) during starting or parallel (12V) during operation/power-off. In my mind this is worse than the CUCV solution of dual isolated alternators, search Google for Series-Parallel-Solenoid.

 

[tim292stro]

For the 12V stereo question, look at this recent thread. The final decision after looking at 24V amps, 24V-to-12V converters, was to go with a vanner. Another user chimed in that they installed #4 (separate 12V alternator/battery).

If you were to try and power some 12V loads from the high-side battery, they would have to be completely isolated ground (probably including the device case), otherwise you're back to the dead short across the low-side battery (high side ground to low-side ground).

It's not my item, but I recommend buying a 100-Amp Vanner from a member who has them listed in the classifieds - about the same cost as a new 12V alternator+battery, keeps your wiring stupid simple and your engine compartment less complicated, charges the low-side battery correctly with the imbalanced loading.