12v +24v ?

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BACAMICK

12v +24v ?

Post by BACAMICK »

this is going to be a wierd question :)

if i had 2x250ah in 24v to run my rv could i then also take of 12v from one side of the 24v batt and run my 12v gear ie waterpump/stove igniter , best pic i could do :) yellow=12v and black =24v


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oldtrack123
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Re: 12v +24v ?

Post by oldtrack123 »

BACAMICK wrote:this is going to be a wierd question :)

if i had 2x250ah in 24v to run my rv could i then also take of 12v from one side of the 24v batt and run my 12v gear ie waterpump/stove igniter , best pic i could do :) yellow=12v and black =24v


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HI
NO , not as simple as THAT
You will end up with one undercharged battery & one over charged battery

What you need is a 24V to 12V dc converter !!

PeterQ
BACAMICK

Re: 12v +24v ?

Post by BACAMICK »

ok thanks , new it looked to simple :)
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Re: 12v +24v ?

Post by BruceS »

Well I did it for 3 years in a truck running all over Australia. (on the same batteries)
To do it successfully you need two voltmeters on the dash showing each individual voltage of the two twelve volt batteries. When you notice one battery is a little bit lower than the other you swap the position of the two batteries.
I found when running a 2-way radio & a radio/cassette that I had to swap every two weeks.
If you leave it too long you tend to 'cook' the highest one & need to ad water to the cells.
I ALWAYS hooked my gear to the one on the Earth side & make VERY sure the cable doesn't get cut/earthed.
Ofcourse that was back in the 80's ..............
Another option would be to run a spotlight or something off the high one to equalise them. (ask T1 Terry about equalising cells)
So, yes it can be done but with modern gadgets it's probably not worth it.
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Izabarack
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Re: 12v +24v ?

Post by Izabarack »

BACAMICK wrote:t... could i then also take of 12v from one side of the 24v batt and run my 12v gear
Absolutely! In practice, I suggest you put in a set up so you can easily change which of the two is your 12 volt source battery. Just keep an eye on how much you are using, 12 volt wise, and regularly change over to maintain about equal charge status in each battery.

Iza
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Re: 12v +24v ?

Post by oldtrack123 »

Hi
I agree with Admin & Iza
You can do it THAT way

But you will need to monitor battery voltage with Accurate voltmeters to two decimal places , to ensure both are equaly charged /discharged
Your load are small ,I expect under 10A , Jaycar have a 24V dc /12Vdc converter unit PART #MP3601[10A surge 7A continious] for around $60 which does the job automaticaly.
The unit does not need a 12V battery If your peak load does not exceed 10A & your continuous isno more than7A
The output is actually regulated to 13.8V
The unit is claimed to be 85% efficient*
PeterQ
Last edited by oldtrack123 on Mon Apr 22, 2013 7:10 pm, edited 1 time in total.
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Re: 12v +24v ?

Post by T1 Terry »

The other option is a DC to DC converter connected across the 2 batteries but feeding into the 12v battery you are using for the 12v supply. It needs to be running 24/7 so it's not a very energy efficient method and the converter needs to be a decent output unit, like 20 amps or more, and both batteries need to be of an equal capacity. Here is the results of not following the equal capacity rule
batteries in hino for sale 0502.jpg
The case is split into each cell cavity because this half of the 24v was extremely overcharged while the alternator tried to full charge the other half of the 24v set up. The exploded battery was something like 120Ah, the other battery was 4 x 120Ah in parallel, or 120Ah and 480Ah linked in series. It did have a 24v to 12v converter linked across them but there was no hope it could ever cope with the alternators output to balance the pair while charging.
An attempt to explain what happens, normally the 2 batteries are balance to an equal state of charge, 14.4v charging in each battery equals 28.8v, the voltage st at the alternator regulator. If one battery is discharged to 12v while the other battery is still full, the alternator will still try to reach 28.8v, if one battery is 12v, the other battery will be charging at 16.8v (12v + 16.8v = 28.8v) till the voltage level of the low battery rises, if the capacity of 12v side is greater than the capacity of the fully charged side, that 16.8v plus over charge will continue for a very long time.
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John M
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Re: 12v +24v ?

Post by John M »

In my original setup I ran 24v motor and House batteries with a 24v to 12v converter, found that the converter used 0.8a to do the conversion (19.8ah per day) doesn't sound like much but soon adds up.
I changed to 12v House and 24v Motor, and charged the house via a Dc to Dc Charger switched via the Ignition, with a 24v 100A relay switching the solar feed off when the motor is running I found the two charging systems tended to get confused and neither charged correctly, cutting the solar feed tended to let the DC / DC charger do its thing, without interference, and when the motor is switched off the solar regulator then does its thing.
"Recycled Teenagers", John, Shirley and Four legged person Beau, travelling in a 7m Isuzu bus towing a trailer. Enjoying the fellowship of the road
oldtrack123
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Re: 12v +24v ?

Post by oldtrack123 »

Hi Terry
The OP does not seem to have a 12V battery, that is why he is trying to get a 12V source ;)
His load seems to be quite small ,the water pump probably being the highest, but I would expect under 7Amps.
The safest, simplest method, IMHO, is a 24 v to 12v converter

Jaycars:
7Amp continuous10A surge $60
15Amp contin 20Amp surge $100

But perhaps it would be better if the OP explained exactly what his set up is ????

[1]is his alternator 24V ?
[2]Are the batteries his crank batteries?
[3]Does he have other means of charging the 24V bank?
PeterQ
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Re: 12v +24v ?

Post by Izabarack »

BACAMICK wrote:this is going to be a wierd question
What ever happened to the KISS philosophy? Even a simple switching arrangement that puts the battery bank in series for 12 volt purposes would negate any concerns about uneven discharge states.

Iza

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