Reply With QuoteWould....
A Traxide SC80 work? Charges the first battery thats not getting charged, THEN charges the second one...
YarnMaster
SubscriberOk, as some of you know I've fitted a smalldiesel engine into my 101... The engine is 24 volt start and charge, the vehicle originally is a 12 volt GS. I've left the engine as 24 volt, utilising its starter and alternator. The system is as follows. The original 12 volt feed from the V8 starter is now connected to a 12v post which is supplied from the first battery. Turn the IGN on and this operates all the normal services (12v), and the original coil lead operates a large relay. The other side of this relay gives 24v power taken from the starter to a second large relay and power to the alternator and new charge light to excite the alternator. Turn the key to the start position, and the second relay is utilised giving the starter solenoid a 24v feed to work. The oil light is running 12v.
The issue is that after several months and 5642 kms the vehicle failed to start today. I removed the battery cover and tested battery voltage.. Both were well above 12 volts. Strange that the vehicle won't turn over. I decided to remove the batteries and check them. Once disconnected and on the floor, I re checked them. The 0 to 12 volt first battery is reading 10.2 volts and the indicator is white indicating a charge is required, the 12 to 24 volt second battery is holding a good 12.9 volts. Having done a very quick Google search, it showed up that as the first battery is getting use, the voltages between the two start to differ, and then the alternator favours the second battery and charges just that one....!!!!?? How the hell does that work? And how do I get around it???
I have two ideas.. 1, Fit a trickle charge solar panel in the roof and feed it to the first battery.. Or 2, Utilise a 'magic box' found on early large Zetor tractors that allows a 12 volt alternator to charge a pair of batteries being run in a 24 volt system...
Thoughts please and cheers in advance!
1995 Mercedes 1222A 4x4
1969 (Now know! Thanks Diana!!) Ser 2 Tdi SWB
1991 VW Citi Golf Cti (soon to be Tdi)
'When there's smoke, there's plenty of poke!!'
'The more the smoke, the more the poke!!'
ChatterBox
Would....
A Traxide SC80 work? Charges the first battery thats not getting charged, THEN charges the second one...
Swaggie
SubscriberHi Simon,
There are 2 things you might like to look at. This one charges a 12V battery from the 24v system, but it assumes you have 3 batteries to work with (2 for 24V and another for the 12V stuff)
http://www.gsl.com.au/battery-chargers-24v-12v.html
Then, there is something called an Equaliser, which may be more what you want:
GSL Electronics : Battery Equalizers
Have a read of the installation notes, which explains how you hook it up:
http://www.gsl.com.au/tl_files/pdf-a...E%20Manual.pdf
Congratulations on purchasing your new GSL Electronics Microprocessor Controlled Battery Equalizer. The equalizer
is designed for use in 24V battery systems where a centre tap is used to supply heavy 12V loads.
This innovative microcontroller based design ensures that both 12V series connected batteries remain balanced during charging even
under highly unbalanced load currents, ensuring the highest possible battery life expectancy and reliability.
HTH
David
BTW - I am using the first unit in my truck, to charge the 12v "house batteries" from the 24v start batteries when the engine is running...
Last edited by spudboy; 29th May 2014 at 09:21 PM. Reason: Extra Info
Swaggie
Yep, when the second battery gets fully charged it prevents the first battery from charging any further.
To run your 12V system, use a 24V/12V converter.
Jaycar has them (that's what I use) and there are many others on the market.
Or you could install a 12V alternator and battery and run a separate system for your 12V.
AT REST
Two 12V alternators, one for the low side battery and one electrically isolated from the engine to just charge the high side battery? Shouldn't be hard to modify an alternator to have a separate earth. Either that or a set of winch type solenoids to connect the two batteries in series just for starting, parallel for 12V charging and running.
TopicToaster
Either Mick_Marsh or bee utey's suggestion will address your problem. It is not a good idea to be running a load of one half of a 24v string of batteries, it will only work for a short time.
Originally Posted by benji
........
Maybe we're expecting too much out of what really is a smallish motor allready pushing 2 tonnes. Just because it's a v8 doesn't mean it's powerfull.
One answer REV IT BABY REV IT!!!
OldBushie
Thanks Basil but no, the SC80-24 could be used but it would still require some form of battery to battery charger.
Hi Sitec and the simplest way is to fit, as suggested above, a 24v to 12v battery to battery charger.
NOTE, you need a battery to battery charger, not a step-down power supply.
Your predicament is something that is commonplace in the motor home industry and I supply two different methods to meet this demand.
You can go with the 24v to 12v battery to battery charger, as others have covered and this is the cheaper setup.
The second setup is a 24v to 240VAC inverter powering a 240VAC 12v battery charger. This setup gives you multiple uses for both devices.
Either way, these will meet your needs.
Now to why you can not draw 12v from one of the batteries in a 24v series setup.
To start, take a low charged single 12v battery. Connect say a 20 amp battery charger to that battery and let the charger charge the battery.
When the battery gets to about 80% State of Charge ( SoC ), the BATTERY, not the battery charger, but the BATTERY will now start to reduce the amount of current it will draws as it gets closer to it’s fully charged state.
You might have a 1,000 amp battery charger, but from around the 80% SoC, again the battery controls the amount of charge it will draw.
Now with this info, connect two batteries is a series setup and do as you are suggesting, and draw a 12v supply from one of the batteries.
BTW this is called Centre Tapping.
The two batteries are wired up with the first battery being between 0v and 12v, the second battery will be between 12v and 24v.
What happens is that the second battery in the series setup will get to a full charged state and will no longer be drawing higher charge currents and will BLOCK any additional current, so the first battery, the one you would be using to get your 12v supply from, just can’t get enough current flowing through it to get it to a fully charged state.
So the second battery will always be in an undercharged state.
This can lead to one of two problems. One problem caused by centre tapping is that the first battery will eventually fail because it is not fully charged properly at any time.
The other problem that can occur is that because the first battery is undercharged, it will be in a lower state and because the second battery is fully charged and not drawing much current, there will be two different voltages across each battery.
EG, two identically charged batteries in a 28v charging supply ( 24v alternator operating voltage ) will have 14v across each battery.
In the case of a lower charged first battery in a series setup and a higher charged second battery in the same series setup, because the second battery if fully charged and BLOCKING the current flow through both batteries, the first battery might only have 12.5v across it but the supply voltage is 28v.
So the remainder of the 28v, 15.5v is now the terminal voltage across the second battery and after a short time, the second battery cooks, and this is even though the second battery is only drawing a low current.
So centre tapping is a No-No.
RoverLord
Go with drivesafe.
you can also use a 24v/12V power supply to charge batteries so long as you fit some kind of current limiting device, I usually use a headlight bulb. of suitable wattage.
If you only have 2 batteries for your vehicle the simplest solution is to fit a 24/12V reducer of suitable amperage to run all your electrical load and ensure that its low voltage cut out is at about the 22-21V range.
Dave
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YarnMaster
SubscriberThanks for the info drivesafe. How much would the Magic Box cost? PM me if required. Here's a pic of another option I have open to me.. Its a 'Monarc Diesel' box, that allows two batteries to be charged as a 12v system in parallel, using a 12v alternator, but when the start key is turned, I believe it separates the batteries and provides 24v to the starter.. I have his one here at work s/h, and I have a new one on the shelf at Dads place in the UK that was bought for the last 101 and never used!....
No idea why the pic is up side down... Its the right way up in the pics file!!
1995 Mercedes 1222A 4x4
1969 (Now know! Thanks Diana!!) Ser 2 Tdi SWB
1991 VW Citi Golf Cti (soon to be Tdi)
'When there's smoke, there's plenty of poke!!'
'The more the smoke, the more the poke!!'
TopicToaster
That will work but it sounds like you need to get rid of your 24 v alternator and change it for a big 12 volt alternator. You need to compare the cost of your Monarc Diesel box and a replacement 12 v alternator to a 24v to 12v converter of sufficient capacity to run your 12 volt loads.
........
Maybe we're expecting too much out of what really is a smallish motor allready pushing 2 tonnes. Just because it's a v8 doesn't mean it's powerfull.
One answer REV IT BABY REV IT!!!
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