12-24V converter vs Splitting?

[Otterav]

Hey,
I have been reading numerous posts about 24-12 converters vs splitting. A friend of mine who recieved his electrical engineering from Purdue and myself were discussing this very subject. His opinion/theory was as follows, if you have a system with a 24v battery a converter is obviously necessary. He then follows up with the opinion that if 2 12v batteries are installed tapping 12v from the first battery is easiest and most effective, since the common ground is available and would simplify the wiring process. Followed by the tapping of 12v from the second battery using dedicated positive and negative wiring. He then said that the draw through either battery would powered by the alternator during running periods. The major concern would be when not running and drawing one battery down and not having enough electricity to start the vehicle. As far as wearing one battery more than the other, his opinion was, variations in manufacturing would be more valid when trying to anticipate battery life, he then said "just swap batteries once a year, that would solve that problem, real or imagined"
I must say that my 24v, military truck shows no reduced battery life, I tap 12v from the first battery to power the camper section and I swap batterys every year, I get about 7 years to a battery set, I am on my 3rd set, I have had the truck since the early 90's. I even use a 110v inverter in the camper section, and we all know how much the current draw is in those things(mine 10+ amps).
Fire away
eric

 

[eleblanc]

Hey,
I have been reading numerous posts about 24-12 converters vs splitting. A friend of mine who recieved his electrical engineering from Purdue and myself were discussing this very subject. His opinion/theory was as follows, if you have a system with a 24v battery a converter is obviously necessary. He then follows up with the opinion that if 2 12v batteries are installed tapping 12v from the first battery is easiest and most effective, since the common ground is available and would simplify the wiring process. Followed by the tapping of 12v from the second battery using dedicated positive and negative wiring. He then said that the draw through either battery would powered by the alternator during running periods. The major concern would be when not running and drawing one battery down and not having enough electricity to start the vehicle. As far as wearing one battery more than the other, his opinion was, variations in manufacturing would be more valid when trying to anticipate battery life, he then said "just swap batteries once a year, that would solve that problem, real or imagined"
I must say that my 24v, military truck shows no reduced battery life, I tap 12v from the first battery to power the camper section and I swap batterys every year, I get about 7 years to a battery set, I am on my 3rd set, I have had the truck since the early 90's. I even use a 110v inverter in the camper section, and we all know how much the current draw is in those things(mine 10+ amps).
Fire away
eric

I couldn't use my truck for 8 years because the preson who was taking care of it, draw 12v from one battery. Even after visit to 3-4 garages in hope they would find the problem of my battery going dead and truck not being able to start, i still couldn't use it...Until i found this site. With the electrical diagram i was able to find bad wiring and taps on the 12V. I since then can use my truck more then 4 hours. IMO don't tap 12v, get a converter or live with the consequences...

 

[Ron R]

Tapping 12V from one of the batteries in a 24V system is bad and will eventually destroy the other battery.
Why? Quite simple. When the batteries are being charged the alternator will try to get the total voltage at the the desired level for a 24V system wich is 28.8 Volts. Each battery then has a voltage of 14.4 volts at wich point it's assumed that that battery is 'full'
The current needed to achieve this is running through both batteries and will continue to flow as long as 28.8 volt is not reached.
So, when one of the batteries is drained more than the other one it's total voltage will be lower than the less used one.
Therefore the less used one will be 'full' before the other one. At that moment that battery will have reached a voltage of 14.4V and the other one will be on a lower voltage. Therefore the alternator is not sensing 28.8V and will continue charging, thus putting more than 14.4Volts on the 'full' batterie. That one then gets overcharged and starting producing gasses. Until the 'lower'one reaches 14.4V and the system voltage then is 28.8 volts. At that moment the alternator quits charging and will just maintain the necessary current to compensate for draw.
If this happens on a regular basis (i.e. when tapping from one of the two) the battery not tapped from will be cooked and destroyed.

Maybe this link is a nice one to read:http://www.a1.nl/phomepag/markerink/12v&24v.htm

 

[BiffS]

how would gel or dry cell batts be affected by this "overcharging"?

 

[Ron R]

how would gel or dry cell batts be affected by this "overcharging"?

Well, I have some knowledge about electrics but I'm defenately not a Battery - guru.
As far as I know these are even more prone to damage due to overcharging, but I was not sure about that. So I did some research on the internet.
There is a lot of info to find but I think these pages give info in an understandable way:
http://www.batterystuff.com/tutorial_battery.html#3


There I found (amongst other things)

GEL: The gel cell is similar to the AGM (Absorbed Glass Matt) style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of lead acid battery. This is probably the most sensitive cell in terms of adverse reactions to over-voltage charging. Gel Batteries are best used in VERY DEEP cycle application and may last a bit longer in hot weather applications. If the incorrect battery charger is used on a Gel Cell battery poor performance and premature failure is certain.