I have installed land mobile stuff in Gov Surplus fire equipment, (right next to Fort Hood) and 24 volt Forestry Service and 24 V street sweeping equipment over the years. I will NOT install any equipment across one battery in a 24 V string.
Take it somewhere else and let them do it. I will not. Without exception, from a RaVo street sweeper to a 2.25 ton truck, the driver will forget and leave the equipment turned on that is across the one battery resulting in that one battery going dead. Now picture this. 2 batteries in a string. One dead, one hot and healthy. Just for sake of discussion. lets say the radio / siren, stuff is across the bottom battery. Neg to GND, Positive to the Radio / Siren stuff AND the Negative of the second battery. Positive of the second battery to the starter solenoid, etc. As long as both batteries are charged this works GREAT. When the bottom battery is dead, and the top battery is OK, and the driver hits the Cole Hersey Switch and tries to crank the engine it is just as though the first battery was no longer there. Remember that the Positive of the bottom battery (now dead) is connected to the Negative if the second battery, thru the starter motor and back to ground..... This effectively does 2 things. 1 - reverse polarity is applied to the dead battery and whatever equipment is hooked to it. 2 - The cranking current will be in excess of 400 amps..... The fuse in the Neg side of the radio most likely won't make any difference because the case of the radio is tied to the chassis of the vehicle - ground. The fuse in the positive side (if present) may save the radio, but most often, the audio PA and RF PA are history as well as any protection diodes - 10 amp protection diode against 400 amp starter current - no contest. So, spring for the Astron or NewMar or whatever DC-DC converter - I like the fully isolated if possible or else I would encourage anyone to stay away from the one battery connection. Forklifts are even worse. Remember it is just a matter of time before stuff gets smoked... Steve NU5D School of Hard Knocks... Ron Wright wrote: > Depending on the load connecting across one battery, the one connected to > ground or the lower of the 2 12 batteries, will work. I would not do is load > is heavy because I am sure the charging system is for both batteries and > draining one much more than the other could upset things. >
