24 volt ????'s

[Engine5]

Ok, I am new to the 24 volt system. How do I hook up radio's that are 12 volt?

 

[m376x6]

First, never consider tapping the top of the first battery (directly grounded negative terminal) which is 12 volts. This always places an imbalance on the system and you end up overcharging and shortening the top batteries life considerably.

The best way is to find what the total power consumption of the radio is. If it is in watts divide the watts reading by 13.8 which is actually the ideal 12 volt system voltage. This will give you amps in case the radio doesn't show actual amperage ratings. Then find a 24 to 12 volt solid state converter that is rated for slightly more amps than your radio will use. I have seen them on ebay. Solid state because these converters have circuitry that regulates the output voltage over a wide range of loads.

The next best method, and one I wouldn't recommend is using a dropping resistor. The reason I wouldn't recommend a resistor is that they are great when the load is constant, such as a light or dc motor. But a radio load varies depending on whether it is idle, receiving, or transmitting. This large variation in loading will change the current draw through the resistor and therefore change the voltage going to the radio considerably.

If you think you've found an ideal candidate for your source but are unsure, drop me an message or email me and I can help you out.

Regards,
M376X6

 

[acetomatoco]

If you are using solid state radios, and not old vacuum tube types, the tapping of 12 v off one battery is just fine for just a few amperes. If you are a fanatic for battery life, you can switch batteries every 6 months or so. Remember that is how the whole darn truck is run in the Cucv series.... The front battery runs all the 12V stuff.

 

[m376x6]

There are many cucv threads dealing with the charging system on them. I must've missed where the thread states it is for a cucv. I believe this was posted in the 5 Ton and up category. Again, for a normal 24 system where there is no discreet 12 volt system available, don't tap off of the center post, even if it is only a few??? amps, it unbalances the charging. For your large truck, not a cucv, stay with what is best for your truck.

M376X6

 

[ida34]

This is also why most cucv's have two 12 volt alts. The two charge the batteries as if they were separate. An imbalance will not be a problem. Only on the other vehicles with a 24 volt alt is there a problem with battery imbalance between two 12 volt batteries.

 

[acetomatoco]

Interesting, how with the alternators wired in series they are able to discriminate between the batteries.... ... However I have tapped 12V off my M35 type trucks for 30 years without problems...but of course I am just a dumb yankee.

 

[acetomatoco]

Another example of 12V taps would be all the M800 series trucks... The connection for the 12 volt glowplug system is right in the battery box and the diagram showing the 12V tap is inside the cover. Don't be overengineering a solution to a problem that does not exist.

 

[Engine5]

Gentleman, I thank you both for your help.

 

[Engine5]

My apologies. I meant, I thank you all for your help. I did not realize how many offered solutions.

 

[m376x6]

Interesting, how with the alternators wired in series they are able to discriminate between the batteries.... ... However I have tapped 12V off my M35 type trucks for 30 years without problems...but of course I am just a dumb yankee.

You called it perfectly! Now go swap your batteries around and read the heading about what trucks the question is dealing with again and quit trying to cover your lack of attention.

Bryan