cruiser skill testing question

[seapotato]

depends, I believe to run two 12v things in series off 24v they have to be of the same draw....or else it won't be 12v to each item, possibly 18 to one, and 6 to the other, that kinda thing. which might be awkward as stereo draw changes with volume.

but my high school physics class was a loooong time ago, so I could be out to lunch on that.

cuz yeah, I have lots of lights hooked up in series on my old truck, driving lights, running lights up front etc, works fine as long as you can handle the whole bank of lights going dead at once. not something you'd want for your headlights.

not quite the same as trying to run batteries in series and parallel at the same time.

cheers,
r

 

[1990 LJ78]

Hey Wayne!!!
You should run this SKILL TESTING QUESTION more often.
Great thread.

 

[shinny]

Take it back to ohm's law..
Voltage = Current * Resistance
and for things in series, the total voltage will add up to 24V, but the current through each unit is what is identical.
(hopefully I don't screw this up!)
V = I * R
24V=I*(R1 + R2) but also V1=I*R1 and V2=I*R2 gives

V1/R1 = V2/R2

Throw some numbers in there, and it becomes obvious that if R1 isn't equal to R2 then V1 can't equal V2.

Does that convince anyone of anything?

 

[crushers]

Does that convince anyone of anything?

yah, that i need to go back to school

 

[sandcruiser]

ok. I knew there was a good reason my idea wouldn't work

but what if you incorporate the correct diodes in there? then could it work?
not that I have a 24v system.... so it doesn't really matter to me!! but just thinkin.

 

[denis]

The diodes won't make up for the different resistance values.

If you put 2 identical, big power components (small resistance value) in series and put a small power component (big resistance value) in parallel with one of the big ones then Waynes idea would work. Say 2 huge amps and 1 radio unit. The radio and one amp combo will have a slightly lower voltage, and the single amp will have a slightly higher voltage.

 

[denis]

Say you have a 30W @12V radio that's a minimum resistance value of 2.4 Ohm.
If you want no more than 14.5V on said radio when the alternator is working at full blast then the lower resistance part on the tension divider must not be below 13.5/14.5 that of the the higher resistance part. Hence the big power items resistance value must be below 0.31 ohm ~ 463W. That's probably not practical in the real world.
Things become easier if the device is of a known, fixed resistance value or at least if we know the extreme values. Then the diodes might be useful for efficiency purposes.

 

[shinny]

Is everyone now using a 'solar converter' as their 12V source? I kind of like the idea of replacing the factory 24V-to-12V converter with, say, one that worked, without having to run some more wires through the firewall. What are you using?