12V/24V with only two batteries?

[andreas kielb]

Though most manufacturers use 3 batteries to power a 12V/24V sleds I saw such systems with 2 batteries as well (..modified EFP's, the Jerry Rig or the custom built sled on http://www.steadicams-for-sale.com



For me it would be better also if there is a way to make my 2-batteries-sled ready for 12V/24V without having to add a third battery (...dynamic balance, weight). But I wonder what is the correct circuit to get 12V and 24v from a bank of 2 batteries.



I assume that this circuit will cause a voltage drop in half of the bank which might shorten the life of battery pack : -->:, is that right?







Thanks,



Andreas

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[cosmin rotaru]

I don't thnik this is how it works...

I think the batteries are probably 24V and you get an 12V output by using some electronics, like "power regulators", or "voltage regulators"...



The 7812 3pin regulator, for example, would take the 24V (maximum 40V) and turn it into 12V. But it will only hold on one Amper.



regulators like the 7812 have 3 pins: one is ground, one is V-in and the other V-out.



Just google for "power regulator" or "voltage regulator".

Cosmin Rotaru

[cosmin rotaru]

info:

http://www.eidusa.com/Electronics_Voltage_Regulator.htm


see the 12V model:

http://www.robotcombat.com/marketplace_elect_other2.html



 

Cosmin Rotaru

[Tim Le]

I'm by no means an expert on electronics, but it seems like Andreas' diagram would work. The only difference is you would have to have a physical switch to make or break the 12V line (or the 2nd battery to get 24V if you prefer). A voltage regulator would also work at the end of the 24V line but it seems a lot of heat would have to be dissipated to drop it down to 12V.

[David West]

is there a way to pull 12v evenly from both batteries using zenner diodes??



(and still give 24v output too)

[cosmin rotaru]

I don't think so

Cosmin Rotaru

[andreas kielb]

Voltage regulators sometimes seem to use zenner diodes.




In the meantime I think the only way to pull 12v evenly from both batteries is to connect them in series and then use a 24V=>12V voltage reducer. I found one on www.conrad.de for up to 8 amperes but it's nearly as heavy as a third battery  





Andreas

[readw]

You need to work out which configuration will draw the most current.  ie will it be the 24v or 12 volt configuration.  



If for example you have determined the 24v circuit will draw the most current then you configure the battery pack for 24 volts.  You then get an converter to run the 12 circuit.  In this example the converter could be anything from a resister (very inefficient) to a high frequency switching switching design (up to 80% efficient).



Generally stepping down voltage is easier to do and usually more efficient.  If the current draw in both configurations is about the same then it would be best to wire the pack in a 24v configuration and run a converter for the 12volt circuit.



If you find that the 12 volt circuit is where most of your current will be drawn than you will need to obtain a inverter to step the voltage up from 12 to 24 volts.  



You will find plently of designs around on the net to do either.  The cost of these circuits is dependant on how much current you will need to draw.



Hope this helps.  

[David West]

if you created two seperate grounds, and then used the zenner diodes in the 12v loop couldnt you end up with a 12v circuit  and a 24v circuit??

[andreas kielb]

Sounds very interesting, David. Could you perhaps make a little sketch for me:

And thanks a lot Warren, it did help  .

On the other hand I just found out that they offer a tiny 24V on board battery for the arri 235
(...which is the only 35mm camera which might come to question).


Andreas