I'm repackaging a Motorola repeater system for a client for better mobile use, and they asked me what it would take to convert it for full DC use. The power requirements seem a bit steep for this unit so I'm looking for some guidance / advice / info that I can relay back to my client. I pulled out the PSU from the unit, and these are the specs listed.

Output: 13.8VDC
7 Amps Continuous
14 Amps ICS @ 20% Duty Cycle (30 sec on, 120 sec Off)

I'm sure its possible to run it off of a battery, but what type of battery would be necessary?

 

The obvious choice is an SLA (Sealed Lead Acid) battery. They are heavy but have high capacity and much lower cost than other chemistries. They are also dead simple to charge.

You need to work out the power requirements for the desired run time to size the battery.

 

Also, you need to know if the repeater will reliably operate from 12V which I expect to be the case.

 

The obvious choice is an SLA (Sealed Lead Acid) battery. They are heavy but have high capacity and much lower cost than other chemistries. They are also dead simple to charge.

You need to work out the power requirements for the desired run time to size the battery.

Thank you. The specs say 13.8 specifically, drawing up to 17amps on transmission.

 

How will the batteries be charged?

 

Thank you. The specs say 13.8 specifically, drawing up to 17amps on transmission.

Yes, 13.8V is the nominal voltage and it is because vehicle electrical systems are regulated to that. But, most 13.8V transceivers operate from 12V as well, since that is the output of a lead acid battery.

What is the output of the transmitter? You say mobile use, is it licensed for that? It sounds like the output is very high and most mobile transceivers will have lower power limits because they are dealing with shared allocations.

 

How will the batteries be charged?

I just spoke with them, they're basically looking to direct connect to a running car, directly to battery.

 

I just spoke with them, they're basically looking to direct connect to a running car, directly to battery.

This is not a good idea. I am also concerned that their license will not cover this sort of operation.

 

Yes, 13.8V is the nominal voltage and it is because vehicle electrical systems are regulated to that. But, most 13.8V transceivers operate from 12V as well, since that is the output of a lead acid battery.

What is the output of the transmitter? You say mobile use, is it licensed for that? It sounds like the output is very high and most mobile transceivers will have lower power limits because they are dealing with shared allocations.

When say licensed, you mean for FCC?

 

When say licensed, you mean for FCC?

Yes, FCC licensing for operation on the frequencies of the repeater and handhelds/mobile units involved.

 

Yes, FCC licensing for operation on the frequencies of the repeater and handhelds/mobile units involved.

Yes, they are licensed. This is a heli motion picture film company.

 

Yes, they are licensed. This is a heli motion picture film company.

47 CFR § 90.247 limits mobile repeaters to 6W output. A 6W transmitter doesn't draw 17A.

(e) In the Industrial/Business Pool, on frequencies designated with an “LR” in the coordinator column of the frequency table in § 90.35(b)(3), the output power of a mobile repeater station, when transmitting as a repeater station on the frequency used for communication with its associated pack-carried or hand-carried units, shall not exceed 6 watts except when the same frequency is also used by the same station for direct communication with vehicular mobile units or with one or more base stations.

In any case, I feel uncomfortable helping with this so I am going to bow out. Nothing personal, best of luck.

 

I respect your stance, thats fine.

Keep in mind, I'm not necessarily looking to do this, if it's not a good idea, I just need to give them specific reasons why.

If you want to further investigate the specifics, here are the models. This is a Motorola model that is readily available with a license. The repeater station model is HLN3052A with radio models D44MJA7JA5AK.

Upon further investigation, transmission amps are 12.5amps, standby 400mA.

 

12.5A for a 40W radio makes sense. It doesn't make sense to power it directly from a car unless you install a secondary battery. The car's electrical system isn't designed for it.

I really feel it is unlikely this system will be legally operated so based on that I will just move on.

 

I just spoke with them, they're basically looking to direct connect to a running car, directly to battery.

Technically that isn't an issue as the mobile units (MaxTrac 300) are 40 watts with direct connection to the battery.
However as YaaKov mentioned you would be operating illegally.