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12 volt tapping off a 24v battery set?
Posted: Wed Nov 10, 2004 8:04 pm
by Rainbow Warrior
Having heard someone say this would be bad for the charging system to unequally discharge the batteries, my question is how bad? Assuming you're only running the stereo, guages etc and maybe the starter motor, not running a winch or anything silly, you could also just rotate the batteries every 6 months or just put up with a 10% reduction in one batteries life.
Posted: Wed Nov 10, 2004 8:15 pm
by murcod
You'll end up killing the batteries- trust me on that one!
I managed to kill the batteries on a relation's Isuzu truck by wiring a 12V alarm to only one battery. Thought I was being smart.
Posted: Wed Nov 10, 2004 11:09 pm
by Santos
murcod wrote:You'll end up killing the batteries- trust me on that one!
I managed to kill the batteries on a relation's Isuzu truck by wiring a 12V alarm to only one battery. Thought I was being smart.
Well yeah, what you did there was have one battery running more items and discharging at a dispropotinal rate which would stuff the recharge...
ever wonder why batteries have those silly little messages
'do not mix old and new batteries or other makes' ?
All you need is a 24v to 12v transformer (
convertor)
trust me i work for the dick
smith powerhouse (electronics)
with an even discharge it shouldn't be a problem as it still draws 24v (which it then converts through the transformer droping the volts and increasing the amps)
truck drivers use the all time to power their portable fridges and dvd players
Posted: Thu Nov 11, 2004 7:14 am
by murcod
The reason I was trying not to use one of the 24V->12V convertors was because it was for an alarm (ie. a device that draws power with the ignition off). Needless to say, those convertors are not 100% efficient and you run the real risk of flattening both batteries if using one for an alarm.
Posted: Thu Nov 11, 2004 9:43 am
by totto
murcod wrote:..........Needless to say, those convertors are not 100% efficient and you run the real risk of flattening both batteries if using one for an alarm.
Don't worry about that, modern converters are fully electronic and very efficient.
I run my alarm off a converter, and the consume is not to worry about unless the alarm keeps going off all the time. The idle consume of the alarm is ecual or lesser than that of a digital clock, which almost all cars have nowaday.
Posted: Thu Nov 11, 2004 11:42 am
by murcod
Hmmmm... Most modern alarms are down around 10mA standby current these days. The convertors often run LED's on them to indicate they're on, so straight away there's around 20mA getting wasted- without even taking into consideration the voltage conversion for the alarm.
Posted: Thu Nov 11, 2004 8:22 pm
by Rainbow Warrior
The reason I was interested was thinking of converting to 24v alternator, lights etc, for running some PLC & industrial sensor gear, but keeping the 12v starter. Easier to get a big 12 to24v converter instead or just run a 240v to 24v power supply off the inverter
Posted: Fri Nov 12, 2004 1:44 am
by Shark
Dont mean to take over your post but if i had a 24v car and i wanted to run a couple of amps and some lights ( fluro) maybe even an engel what size convertor should i go for?? 10amp, 20amp or 30amp??
A simple answer to that would be great.
MArc
Posted: Fri Nov 12, 2004 9:33 am
by Rainbow Warrior
Shark wrote:Dont mean to take over your post but if i had a 24v car and i wanted to run a couple of amps and some lights ( fluro) maybe even an engel what size convertor should i go for?? 10amp, 20amp or 30amp??
A simple answer to that would be great.
MArc
30A, as I think an Engel draws around 7A and triple that on starting current.
Posted: Tue Nov 16, 2004 10:38 am
by Utemad
Our Engel fridges run off 12-24 volt DC and 240 volt AC.
So just run the Engel from 24VDC. No probs.
Posted: Tue Nov 23, 2004 9:01 pm
by TX4000
The new 24 - 12v converters from GME are switchmode, very efficient.
check em out.
Posted: Mon Jan 24, 2005 9:53 pm
by Tas_Dean
I know this is a bit late but.... You'll never get a convertor that will run a starter motor!
The best way to achieve this is to use two alternators, 1 at 12v charging a 12v battery, and one at 24v to run your 24v battery bank. In this layout, you'll need 3 batteries (minimum).
Just out of interest, what do you intend to run in a car with a plc? I'm rather intrigued, I have done a lot of work with PLC's.
Posted: Tue Jan 25, 2005 9:42 pm
by Rainbow Warrior
Tas_Dean wrote:I know this is a bit late but.... You'll never get a convertor that will run a starter motor!
The best way to achieve this is to use two alternators, 1 at 12v charging a 12v battery, and one at 24v to run your 24v battery bank. In this layout, you'll need 3 batteries (minimum).
Just out of interest, what do you intend to run in a car with a plc? I'm rather intrigued, I have done a lot of work with PLC's.
A crazy idea of pneumatic suspension, got to get the hardware first, probably never happen. Just thought I'd do the easy way and run everything 24v and tap off from one batterry for the starter & stereo.
Posted: Wed Jan 26, 2005 3:33 am
by totto
Rainbow Warrior wrote:........................ and tap off from one batterry for the starter & stereo.
This has been covered before, but obviously can't be said often enough: Even running a stereo tapping from one battery will get you into problems after some time. Tapping for a starter will get you in trouble after just a few starts.
Tapping down one battery causes this battery never to be fully recharged and the other one constantly over-charged - eventually both will be ruined......