Batboard

My unit received a 1997 F350 Wheeled Coach Type I retired ambulance (replacing our old 1989 Type III) for use as our SID response vehicle.

During the transfer of equipment, we noticed a 6 outlet fuse panel mounted in the electronics compartment and wired our 3 Motorola radios (all Spectras: 1 each in VHF, UHF and 800). Here is the problem - when all three radios were powered up, the VHF and UHF would shut off and restart when their mike was keyed up for a radio check. We only keyed one at a time. Is this due to a lack of power? If so, any suggestions to correct it?

Since these are donated radios our Radio Shop will not work on them so it is up to us or find the funds to take it to a contract shop. Thanks.

My suspicion would be either small wire feeding the fuse panel, or a too-small circuit breaker in the line feeding the fuse panel.

When dealing with an unknown vehicle, it's important to understand what you're wiring to and what limitations it imposes. Wiring to a fuse panel blindly isn't the best move. Trace the input side, figure out where it goes and what protection if any is inline, and you'll likely find your answer.

Does sound like power issue... when you keep up the power would drain. But you would see a fuse blown if it is too small. It could depend on what power management system is on the ambulance (if any) that could shut down devices when it detects too much drain, meaning that it would not be on high enough setting to handle the radios.

First of all and not knowing the radio shop your talking about, my guess is that they
are probably a Motorola shop. My personal position would be to tell the radio shop
that what difference does it make where the radio came from. If I pay you to do
the service work, I would expect you to work on any radio I bring you. If their
position remains stuck up, I would seriously consider dropping them and going to
another shop.

On the subject of the Motorola radios going into a reset cycle, this normally only
happens with low DC supply power. Try putting a volt meter on the power bus
and watching the voltage. Key the radio and watch what happens to the voltage.
If it goes much below 12 to 11.5 volts, these radios will do a power on reset just
like they are designed to do.

If you do find a low voltage issue, go right back to the battery and watch the
terminal voltage there. You could have a couple of simple problems like a bad
high resistance battery and or an alternator that can't maintain the voltage.
Batteries that are over 3 years old tend to develop an internal high resistance
and won't be able to maintain voltage under loads.

Your alternator might have a bad diode in it and again like an old battery, can't
maintain voltage under load. Some mechanic might have turned the idle down
on the engine to save fuel. If you get below the output RPM curve of the
alternator, it will never keep up under even a light load. Simple way to check
this out is have the engine running at an idle. With you digital meter on the
battery terminals, start turning on the normal vehicle load. Read the voltage
with nothing on. Then turn the headlights on on low beam. Then go to high
beam. Next turn on the heater fan motor on high. Last, turn on the wipers.
Some place along the steps here you may or may not find where the voltage
at the battery starts to drop. If you find it goes below the 13.6 volts or so
right at the start, you need to fix that issue before going any further.

Jim

dpd4703 wrote:My unit received a 1997 F350 Wheeled Coach Type I retired ambulance (replacing our old 1989 Type III) for use as our SID response vehicle.

During the transfer of equipment, we noticed a 6 outlet fuse panel mounted in the electronics compartment and wired our 3 Motorola radios (all Spectras: 1 each in VHF, UHF and 800). Here is the problem - when all three radios were powered up, the VHF and UHF would shut off and restart when their mike was keyed up for a radio check. We only keyed one at a time. Is this due to a lack of power? If so, any suggestions to correct it?

Since these are donated radios our Radio Shop will not work on them so it is up to us or find the funds to take it to a contract shop. Thanks.

just another thing to check. You might try checking your grounds to make sure they are good. I have seen issues with radios turning off when you key them up because they are using the coax as a ground because the radio ground is loose/missing/broken. Easy way to check is to put your ohm meter where your radios are gorunded to and a good ground. should come back 0 ohms ish.

Wheeled Coach has a particularly good electrical wiring system. In the patient compatment behind the captains chair you should find a main electrical cabinet. The main buss bar is fed with battery cable direct to the vehicles batteries/alternator. All three Spectras should get their power from the main bar there through individual in-line fuses. The control heads (if any) can be powered through the fuse panels you mentioned. There is also a central ground point in that compartment which would be a good ground source for your spectras. Wired properly, this vehicle should be able to support all three mobiles simultaneously if need be. Multiple radio installs are typical in ambulances, so there should not be any issue. Hope this helps.

Bill

Check the voltages and then trace all the wiring and make sure it's adequate. Ensure everything is properly fused while your in there, as it sounds like you may not have changed fuses. Check for any loose grounds.

The wire feeding the fuse block is too small, or has some high-impedance connections in it. When you key the radio, you start drawing lots of current, which develops a voltage drop across the wire or bad connection. This drops your available volts too low, and the radio resets.

I see this all the time in vehicles that have had new radios retrofitted onto the old wiring.