Power Supply for SSB in 24v Boat

[Dockhead]

I'm surprised that marine SSB radios seem to all be 12v, despite the huge power (30 amps) they can consume while transmitting. 24v would be more efficient! So there's nothing for it but to buy a large DC-DC converter. Any hints on choosing one? Should it be galvanically isolated, or does it matter?

[Zanshin]

Dockhead - I was surprised as well that there was no 24V version for my ICOM.

Since my 24V house bank is far bigger than the 12V system, I went ahead on had a big 12V-24VDC converter installed. Apart from the cost and size of the unit, I believe this converter keeps the power supply to the ICOM SSB much more stable and helps improve reception.

One of the forum members, Bill Trayfors, did the installation for me and also recommended the converter, I don't have the details here but will look it up, see Winter 2011-2012 Blog and Diary 2011-11-19 for a picture of the process.

[goboatingnow]

I suspect it would be cheaper to put it a battery and echo charger then buy a good quality dc dc high output converter.

And no there's no advantage to having galvanic isolation on the converter.

Dave

[Dockhead]

Thanks for the replies. I'd be interested to see your setup, Zanshin. Dave, my main engine and genset are started with 12v systems which are completely separate (own alternators and chargers) from the house. It wouldn't be too hard to wire up to one of those. But Peukert would rear his ugly head on transmit with such a small (single battery) bank. And I like the idea of a stabilized supply. A 30 amp dropper isn't that expensive, especially consider that I would save the cost of a longish run of heavy copper cables capable of transmitting 30 amps of power at 12v.

[Dockhead]

Victron 40 amp stabilized dropper costs 101 pounds in the UK (about $165), plus VAT I guess. I think that's quite ok, and I have space for it (very large electronics bay behind nav table). Only problem is it outputs 12v; I reckon the radio probably wants 13.5v. May have to go with MasterVolt.

[Zanshin]

Dockhead:

In my case the 24V bank is (mostly) below the nav station, the 24VDC cable run to the Newmar DC-DC converter is only 3-4 feet. From there, the 12VDC supply cable to the ICOM unit is only about 2 feet.

After a bit of going back an forth regarding price and how many continuous amps really are needed, we finally agreed on using the Newmar 32-12-35A. The main 24V circuit breaker is located in the same area, so the converter is hard-wired into the system right after the breaker and the constant drain of 50mA when not used is acceptable to me. The unit is oversized so that I can hook in any 12VDC devices that need a regulated current (perhaps a 12V TV or computer system or additional LEDs without resistors) without worrying about overloading the system.

Ok, I've searched my e-mails and found the DC-DC converter that we decided upon:

The Newmar 32-12-25A for about $500. I gather that this is the same unit used in commercial and military applications so should be plenty rugged enough for my purposes.

See Newmar DC-DC Converters

[CAELESTIS]

Rather than a converter, I simply installed a designated battery for the SSB. The SSB is on its own circuit. I used a Blue Seas combiner for the charging as the battery sits inches from my identical engine start battery.

[Zanshin]

Caelestis - how big a battery did you get? I would have expected even a 100Ah battery would get a large temporary voltage drop when transmitting at 30A for a given length of time.

[CAELESTIS]

I forgot the exact battery size, but either a group 27 or 31. The same as my engine start battery.

[hellosailor]

Dockhead, I suspect it is an engineering issue. SSBs will be solid state these days, and the internal circuits will not require higher voltage for anything. The power transistors, etc. probably don't need the higher voltage, which would mean raising prices or changing designs to work the radio on 24V. So the manufacturers are just leaving that as an extra cost for those of you who have 24V systems.

[Cheechako]

Originally Posted by goboatingnow

I suspect it would be cheaper to put it a battery and echo charger then buy a good quality dc dc high output converter.

And no there's no advantage to having galvanic isolation on the converter.

Dave

I used a Motorcycle sized battery for my HAM rig even though the boat was 12v. Keeps the noise out of the system. It was in a small cabinet near the radio, charged by a large wall wart style charger.

[Cruiser2B]

Originally Posted by Cheechako

I used a Motorcycle sized battery for my HAM rig even though the boat was 12v. Keeps the noise out of the system. It was in a small cabinet near the radio, charged by a large wall wart style charger.

Thanks for the idea, I had thought about a back up supply. I would use this as a back up as I have an 8D 12v battery as house batt. How long can you run your radio on RX with it? How long does it last when you TX? Just curious.

[Cheechako]

I no longer have that boat, but the charger had a red, yellow , green indicator on it for state of battery charge. I just watched that. I would use paktor pretty much daily and really never had an issue during transmit. I still have the charger here somewhere.... I think it might have been a computer device originally....

[Lake-Effect]

Originally Posted by CAELESTIS

Rather than a converter, I simply installed a designated battery for the SSB. The SSB is on its own circuit. I used a Blue Seas combiner for the charging as the battery sits inches from my identical engine start battery.

This what I would do, too. Alot cheaper than the DC-DC converter, and is one more battery available for 12 v loads and as a backup starting battery.

I don't think a suitable 12v battery's voltage would sag significantly on a 30A load, and I expect that any marine SSB set would be designed to cope with that anyway.

[goboatingnow]

yes and you get to comply precisely with ships licenses that often require a battery backup or independent supply , a double win.

Dave