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Old 12-11-2018, 18:21   #1
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do I really need 13.8 volts for Icom M802 SSB radio ?

I was reading the installation instructions for the Icom M802 SSB radio. It says to connect DC power wires to a "stable 13.8 volt supply". Ours has a pretty clean connection isolated from the rest of the DC power distribution panel. It is properly fused and circuit breaker/switched. But I assume like ours, most SSB radios installed on boats do not have a DC to DC voltage buster to increase the voltage from the typical 12.50 to 13.0 volts from the batteries up to the stable 13.8 that Icom recommends. So any thoughts as to how important it is to try and increase the voltage and if so what is on the market to achieve that ?
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Old 12-11-2018, 18:37   #2
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Thought one of the design features of the 802 over ham radios is that they worked on low voltages where Ham radios might notl. The ham radios are supposed to output fewer watts as the battery voltage drops. Can't say that I ever noticed it as I've always been able to get through even with voltage at 12 + or - with my ICOM 718 ham radio. So no, you should be fine on the radio at 12.7v or whatever resting voltage is on your battery and even get out with voltages at 12v or below though mabe with not as strong a signal.
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Old 12-11-2018, 20:20   #3
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

My volts can get really low after a long attempt at an Email. I give up at about 12.6v.
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Old 12-11-2018, 21:47   #4
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

The ICOM M802's recommend voltage is 13.6V +/- 15%, or ~11.6V min
For the ICOM IC-7100 (which I own) is 13.8V +/- 15%, or ~11.7V min

So the marine version get's you a bit lower, but not much. That said, it the spec... they may do better than the min voltage in the real world.
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Old 12-11-2018, 22:19   #5
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

I never had a problem with the 802 with voltage bellow 13.8. To be honest I doubt I often had 13.8 when using it.
Generally sending emails over the pactor is not best done in the middle of the day and most of the nets are in the early am.....before hrs of solar panel output to make up the amps for keeping the beer cold.
Obviously make sure you can get plenty of juice to it. No long runs with voltage drop, they suck up the amps when transmitting!!
So, in my experience, no.
I think you will get a lot of experienced comments on this question.
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Old 13-11-2018, 10:20   #6
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Year's ago, a friend had a battery built with one more cell, so the voltage was always high, even on transmit.
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Old 13-11-2018, 10:34   #7
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

I found with my old SEA 235 SSB, if battery voltage was low, I had trouble transmitting via Pactor modem. Always tried to make sure batteries were charged before checking email.
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Old 13-11-2018, 10:49   #8
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Simple answer: YES
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Old 13-11-2018, 10:59   #9
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

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Originally Posted by moseriw View Post
Simple answer: YES
REAL simple answer is in post 4 above: 13.6 +/- 15%!

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Old 13-11-2018, 10:59   #10
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Quote:
Originally Posted by moseriw View Post
Simple answer: YES
I would be very surprised if the 802 has less voltage tolerance than other ICOM SSB radios. Our experience is that the ICOM M700 continues to transmit with very low voltages (down to 11.6). When the sun is shining and solar is plentiful, voltage is no problem. Night time, and when you have not been motoring all day, the voltages can get low on our boat, the ICOM continues to transmit, uses about the same DC Amps of power during transmission, (often 20-30 amps), and our Pactor connections seem more affected by weather than voltage.

So I would say that your normal range of battery voltages will work.
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Old 13-11-2018, 11:13   #11
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

I’ve had an ICOM M802 w/pactor modem on my boat since 2008, and know I’ve never supplied 13.8V to the radio, which works perfectly. I’d be certain that you do not undersize the positive and negative power supply cables between the supplied power cable, and connect the connecting cables directly to your batter terminals. You should have no problems ala the 13.8v spec.
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Old 13-11-2018, 13:43   #12
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Best way to understand the impact is to connect via Winlink to a data server and then vary the voltage from an external power supply from 12V to 14V and observe the changes in the data rate. Everything else is just people talking about their perception of what an excellent connection means.
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Old 13-11-2018, 14:05   #13
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

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Best way to understand the impact is to connect via Winlink to a data server and then vary the voltage from an external power supply from 12V to 14V and observe the changes in the data rate. Everything else is just people talking about their perception of what an excellent connection means.
When connected to Sailmail with my 710 the data rate can vary substantially while I have steady voltage... I think its called propagation....

I have also found that if motoring in smooth seas ( not something you would do when running under full sail ) I can alter the data rate by altering my heading.... if pointing bow in general direction of station = poor ... point stern at station far better.... using the backstay....

I have repeated that experiment several times with the same result..

I'm with Jim's +/- 15% .. my batts are invariably in the 'low 12' region
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Old 13-11-2018, 14:49   #14
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

Quote:
Originally Posted by NirvanaBob View Post
I’ve had an ICOM M802 w/pactor modem on my boat since 2008, and know I’ve never supplied 13.8V to the radio, which works perfectly. I’d be certain that you do not undersize the positive and negative power supply cables between the supplied power cable, and connect the connecting cables directly to your batter terminals. You should have no problems ala the 13.8v spec.
While we are on the topic of the M802, I finally finished the installation of my 802 and Pactor modem (only took me 7 years!) and then went to the ICOM manual to learn how to operate it and found the manual is next to useless. Anyone got any links or suggestions for a Dummies guide to operating the 802 and / or Pactor.

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Old 13-11-2018, 15:19   #15
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Re: do I really need 13.8 volts for Icom M802 SSB radio ?

I have a Kenwood TS-480SAT 100 watt HF SSB Ham radio aboard. I use a battery booster that has an adjustable floor voltage, where any voltage above 10 volts in produces an adjustable minimum output voltage. I just let my bats drop to 12.0 volts, transmitted (the max power out was less than 100 watts - as I recall about 60 watts), and adjusted the floor voltage for 100 watts output. The voltage turned out to be 13.2 volts. So now I had maximum power down to 10 volts on the bats (not that I ever intended to take my batteries that low).

Now that I have a lithium (LiFePO4) battery, it's no longer an issue since the lithium maintains 13.2 volts across nearly all of its discharge curve with very little voltage sag at the required 30 amps for transmitting. You might want to consider a lithium battery for your radios. You'll need some other electronics to properly charge and protect the lithium battery. If you dedicate the battery to just your radios, you'll also have an emergency power source if all your other power sources fail.


I also found my Tiller Pilot A/P stopped misbehaving after I switched it to the lithium for power. I'd been blaming the HF transceiver, when in fact the problem was caused by voltage sag while transmitting.
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