Btw, I did try one of these simple 24v to 12v converters to be able to charge my phone - which did not go well. Both the converter unit and my phone got extremely hot.

Skärmavbild 2016-12-15 kl. 16.02.43.png
 
Tap a supply from one battery (assuming you have twin 12V batteries) - is it just fairly low wattage stuff, you would not want to draw two much from a single battery in a twin battery setup but a little won't cause an issue.
 
If you take power form one battery make sure its the one nearest earth otherwise if you have a short you may stick 24v through your 12v kit.
Tbh power from one battery long term is bad news for the battery concerned.
 
lynall said:
If you take power form one battery make sure its the one nearest earth otherwise if you have a short you may stick 24v through your 12v kit.
Tbh power from one battery long term is bad news for the battery concerned.
Click to expand...

If he is only pinching 10-20W for a phone charger it will not make a difference.
 
True but the op mentions a fridge and a sound system, sound system not to bad but a fridge has got to pull some power?
 
Split the 24v into two 12v loops. Providing the 24-12v loop is isolated from ground it will work fine.
 
lynall said:
True but the op mentions a fridge and a sound system, sound system not to bad but a fridge has got to pull some power?
Click to expand...

I read gadgets and assumed it was a charger or nav! White appliances in his Landy I did not think of!

So yeah, I would not want to load up a single battery in a series install with that much load.
 
If its two batteries, then you can have a separate circuit running on one. You would have to check the charge voltage from the alternator across the battery though, i assume the alternator produces 24v which is split across both. Also worth considering that one battery could discharge a lot quicker than the other, and unless you have some fancy dual charging system you could over charge one of the batteries. Which would kill it pretty quickly.

The issue with a separate system is that they'll remain on even with the ignition off, unless you ran a relay from the ignition to switch it off when you remove the key.

What about a system of running all the cars electrics with the batteries in series (24v) as it is now, and the running the auxiliary equipment with the batteries in parallel (12v)?

No idea if that would work but it would give you the correct voltage.
 
philsefo said:
If its two batteries, then you can have a separate circuit running on one. You would have to check the charge voltage from the alternator across the battery though, i assume the alternator produces 24v which is split across both. .
Click to expand...

That's what I was thinking if he wanted a small 12V circuit, the system will be (is is with nearly all 24V systems trucks included) 2 x 12V batteries in series, as far as the system is concerned the battery is 24V - much like a 12V battery is actually 6 x 2.2V cells so really all it is is 12 x 2.2v it's just that they are not all in the same case.

Now the issue with this is that the batteries should always be bought in pairs, same make, model, batch if possible because you want all the cells to be matched. If you start pulling current from one of the batteries then the potential voltage across that battery will now differ from the other, this will have the result that it will want more power (voltage & current) from the alternator and it will also drag down the charge state of the other battery.

Remember hearing you should never mix batteries in toys and remotes and things, it's the same thing here. By depleting one differently to the other you have effectively just mixed batteries.

A better option here may be a dedicated battery with it's own alternator or 24-12V charge circuit.
 
discomania said:
That's what I was thinking if he wanted a small 12V circuit, the system will be (is is with nearly all 24V systems trucks included) 2 x 12V batteries in series, as far as the system is concerned the battery is 24V - much like a 12V battery is actually 6 x 2.2V cells so really all it is is 12 x 2.2v it's just that they are not all in the same case.

Now the issue with this is that the batteries should always be bought in pairs, same make, model, batch if possible because you want all the cells to be matched. If you start pulling current from one of the batteries then the potential voltage across that battery will now differ from the other, this will have the result that it will want more power (voltage & current) from the alternator and it will also drag down the charge state of the other battery.

Remember hearing you should never mix batteries in toys and remotes and things, it's the same thing here. By depleting one differently to the other you have effectively just mixed batteries.

A better option here may be a dedicated battery with it's own alternator or 24-12V charge circuit.
Click to expand...

Yeah if one battery is fully discharged then the other will force a current through it, but the wrong way, destroying the battery!
I actually wrote a dissertation on this but yeah i've forgotten most of it, including the correct terminology.
 
sirredarre said:
Btw, I did try one of these simple 24v to 12v converters to be able to charge my phone - which did not go well. Both the converter unit and my phone got extremely hot.

View attachment 112980
Click to expand...
DC to DC converters been around for a long time and I have built one as part of my electronic tech program in the mid 80ies. There are different brands and qualities, current ratings etc.

Because you had issues with the one you listed does not mean that the idea bad, just get a good quality one with the proper load rating you need. Make sure it is properly filtered...you could also add a 1F Capacitor to assist with filtering and load demands on the 12V output side.
 
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