ICOM 7300 - run on battery?

Discussion in 'General Technical Questions and Answers' started by OE1FLS, Aug 25, 2020.

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1. OE1FLSPremium SubscriberQRZ Page

Dear OMs and YLs
I've an ICOM 7300 which works perfectly on an external 13,8V DC power supply.
However, when I try to run it on an external 12V lead battery (24Ah), the input voltage (measured on a powerwerx multimeter) goes down from 12,5V to 11,3V as soon as I push PTT; and the output power is just about 10 Watts PEP.
So far, I could not identify a reason for that.
Does anybody have an idea?
Thanks in advance,
73 de Florian OE1FLS

2. K0UOPlatinum SubscriberPlatinum SubscriberQRZ Page

Icom radios do not like voltage that is lower than 12 volts at all/ strange things happen. On my RV sometimes the voltage gets low before the sun kicks in in the morning and I have a similar problem I do use a battery booster

your battery is probably not good either if your voltage drops that quick

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3. AI5DHHam MemberQRZ Page

You already identified the problem and just do not know it yet.

You have at least one design issue, and could be compounded by too small and long of wire, and/or a weak battery. But here is the bottom line. Batteries have maximum charge and discharge rates. This is especially true for discharge cycles. They are expressed as C-Rate, a measure of the rate at which a battery is discharged relative to its maximum capacity. Where C = Battery Amp Hour capacity. Example if you have a 100 AH battery in theory can be discharged at 100 amps for 1 hour until discharged. This would be 1C Rate.

So here is the problem, sounds like you are using a Pb battery. A Pb battery C-rate is very low. On the order of C/10 to C/6. You have a 24 AH battery, and a C/!0 rate = 24 AH / 10 Hours = 2.4 amps, up to maybe C/6 = 24 AH / 6 Hours = 4 amps. You are demanding more current than the battery is capable of delivering without excessive voltage sag you are experiencing. Your battery is likely to small for the job.

Additionally if you used too small of gauge of wire or too long of a run are paying the price with voltage loss on top of undersized battery.

Super easy to test. Measure the voltage at the battery terminals when in RX and record it. Key the mic and observe voltage on the battery terminals. If it drops more than 1/8, you know for fact you have a battery issue. Repeat test at radio positive and negative input terminal. If the voltage on TX is more than 1/4 volt lower than battery when in TX, you know you have a wiring issue on top of a possible battery issue.

Now gogetter done and report back.If you did your job right, there should not be more than 1/4 volt drop at the radio. Do the test and you will see where it needs work.

Last edited: Aug 25, 2020
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4. K0UOPlatinum SubscriberPlatinum SubscriberQRZ Page

Good point about wire size as I just assumed you were using the standard Icom cable. But without complete information I shouldn't assume anything!

5. WB2WIKPlatinum SubscriberPlatinum SubscriberQRZ Page

A 24AH battery normally would not support an IC-7300 transmitting at full power.

Try a 60AH battery and see what happens.

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6. VK4XJBHam MemberQRZ Page

My 7300 is only ever run from battery. The radio shuts off around 10.5V. Mine has continued working when the voltage at the radio has dipped to 11.6V which is only 0.1V below spec. Still showing 100W output down to 11.8V at the radio.

With you saying pep I am guessing ssb. Keying up on ssb and not speaking will be around 5A. If that drop is with 10W then maybe 8A from the battery. If you are using the stock power lead I will go with your battery is not up to the task.

I have been doing 100W off lead acid batteries for over 2 decades. Big enough battery and good power lead have not had a problem. The smallest I used had an estimate Ah rating in the 50 to 60Ah range. Currently using a 100Ah deep cycle which is my 1st with a Ah rating. Any complaint I have had revolved around the drop across stock power leads at full power. The icom lead is 3m long and looks like the wire is #10. Using a voltage drop calculator I found online it says 12.6V + 20A is 0.39V drop. Add the total 0.28V drop I am seeing across the fuses that is 0.67V at full power and you are running no where near that. That drop is consistent with what I found when my power lead was still stock.

If I was running from a 13.8V psu I would not care but running from battery these drops add up. The drop you are seeing at 1/10th the power is excessive.

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7. WB2WIKPlatinum SubscriberPlatinum SubscriberQRZ Page

Although I "can" run most of my station from 12Vdc (batteries), I choose not to do so for lots of reasons.

One is, although most of my gear can actually "work" down to 11.2 Vdc or so, the transmitters no longer meet spec for IMD, as they were designed for closer to 14Vdc. On CW, this doesn't really matter (ditto for FM or RTTY) but on SSB it matters quite a lot.

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8. AI5DHHam MemberQRZ Page

No argument here, but screams loud and clear your radio is not designed to operate from a 12 volt battery. It it were would work within universal spec down to 10.5 volts. If the radios were certified to work in military or industry would have to operate the full operating range of a battery system.

12 volt = 10.5 to 15 volts
24 = 21 to 30 volts
48 = 42 to 60 volts

That is the operational voltages encountered in an operational battery system. From fully Discharged to Equalize voltage. Imagine telling a customer their radio is not to be used with a battery system? If they did would not make any commercial sales as it is requirement.

9. WB2WIKPlatinum SubscriberPlatinum SubscriberQRZ Page

Most of the "12V" ham rigs were really designed to be used at close to 14Vdc and are often specified at 13.8Vdc +/- something.

Some "QRP" rigs will work okay down to 9Vdc! But they usually specify that, too.

I've had VHF-FM ham transceivers that run 50-70W output power at 14Vdc and only about 2/3 power at 12Vdc, but as long as they still lock on frequency and "work," they're fine. IMD isn't an issue on FM and losing a dB or two in output power doesn't matter much.

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10. OE1FLSPremium SubscriberQRZ Page

Dear All, thank you so much for your quick replies!
I will do some measurements today and report.
I've attached the data sheet for the battery; the discharge curves include even a graph for 72A.
Will come back later.
73 de Flo OE1FLS

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