Radio for my M35

[Edward42]

Hi. I'm new to the forum and not sure where to post this question. Several years ago, I found a French STTA ER-79A dated 11/76 and the STTA DY-27-B power supply that goes with it. I have just now been able to have time to see if I can get it up and running. I want to use it as a display with my M35. As I understand it, the ER-79A is the French equivalent to our Prc-10 except with slightly different frequencies. I have read on the net that the DY-27-B will power it using 8 D cells wired in series for 12 volts. When I got it, it came wired with the male plug like what would go in the cigarette lighter female hole in the old days. I guess a better way to say it is it is set up I think to use a 12 car battery receptacle. Also it came with two of the black plastic battery boxes (each set up for 4 D cells) so the DY-27-B could use D cells instead of the car battery plug. I guess these are two separate ways the DY-27 could be powered. My question to you folks that know a lot more than me about this stuff, is would it hurt to use the 12 volt car battery setup because that has higher amperage than the 8 D cells? Not sure if I said that right but I don't want to blow up my radio. Just because the DY-27 came setup for a car battery doesn't necessarily mean the guy ever really tried it or maybe he did and it blew the radio. It would be more convenient for me to use a car battery but don't want to hurt the radio.The car wiring setup from the previous owner does have an inline fuse of 5A 32 V which sounds way to high. Any thoughts from y'all would be most welcome!!!

 

[SCSG-G4]

The inline fuse sounds about right to limit the power going to the radio - it's 5 amps up to 32 volts, so either more amps OR more volts will cause it to blow, protecting the equipment after it. Unless you are going to have a separate battery just for the radio you will need to be very careful how you get the M35 voltage (25.6 V) down to the radio. There are other threads that cover this subject which include how to do it and what to purchase to do it correctly. The field expedient method is to hook leads to the first battery (from the positive lead) and use the radio sparingly. This will allow the first battery to be drawn down by the radio and be recharged from the generator/alternator while the engine is running. Doing it the other way around (taping off the second battery) will wind up cooking the first battery (overcharging it) while the second battery is still not up to full charge. The real problem comes when the voltage across each battery differs from the other by more than .5 volts. That is when the damage really accelerates. Most people who want to run 12 V accessories in a 24 V M-35 wind up using three group 31 batteries and a dual voltage alternator (both 12 and 24 v), so the accessory battery is charged separate from the ones used to start and run the truck. More information may be found in the 'camper build' threads as they have the most discussion on using 12 Volts

 

[Valence]

Hello Edward42, and welcome welcome!

Everything that SCSG-G4 is correct.

Just because the radio is hooked up to a power source capable of delivering higher amperage to the radio doesn't mean the radio WILL draw more. The fuse is protecting the radio and will blow if the amperage or the voltage exceeds the specified ratings (5A or 32V).

Ways to power 12V accessories in your M35 (a 24V system):

• 24V to 12V converter
• Battery Balancer
• 12V/24V Dual voltage alternator
• Separate 12V alternator and a 3rd, separate, battery

Obviously the simplest, and cheapest solution is a 24V to 12V converter rated for the demands of your 12V accessories. If the only 12V accessory you plan to add is the radio, your power requirements are pretty low. I don't know what the power draw of that radio really is, but using the 5A fuse as a guide you'd need a 60 Watt (continuous, not peak) converter (12v * 5A = 60W), minimum.

 

[Edward42]

Thank both of you very much. I was hoping for it would work with the truck. Now I need to get to work. Best regards!!!