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Author Topic: HF radio for batt voltage  (Read 8704 times)
W8JX
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Posts: 12081




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« Reply #15 on: March 26, 2017, 12:07:50 PM »

I know I am not sitting on top of the cap when it explodes

I trust though you're not stupid enough to intentionally hook it up backwards like in the video.

I offered W8JX to empirically bench test his capacitor suggestion but so far he hasn't come through with any specifics for the proper capacitor.  The offer still stands.


Mark K5LXP
Albuquerque, NM

Next time you make a post here from a PC or laptop and surf web, thank electrolytic caps big time as it would not be possible without them. Modern systems use a very low CPU core voltage and at a very high amperage load that can go from almost nil to max load many many times a second as CPU constantly throttles up and down. The power rails for CPU have multiple electrolytic caps in parallel with these rails to stabilize voltage during these wild load swings that would not be possible without them even though some insist that they do not help. I guess modern audio buff are higher up food chain that some hams because they understand how they can help and use them while some hams have a brain fart on subject and it escapes them.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
NQ3M
Member

Posts: 48




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« Reply #16 on: March 26, 2017, 12:11:53 PM »

The MFJ-4416C battery voltage booster will supply 13.8 volts down to an input voltage of 9 volts.

   KH6AQ, formerly WX7G
This, ^^^^^^^^^^^^ but a quality antenna an feed line will trump even that.
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G8YMW
Member

Posts: 661




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« Reply #17 on: March 27, 2017, 04:05:52 AM »

But unreadable audio will trump everything.
In the case of the few radios that are tolerant on lower voltages, I would agree but it seems most radios do not like the voltage supplied when the engine is off.
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73 de Tony
Windows 10:  Making me profane since March 2017
W8JX
Member

Posts: 12081




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« Reply #18 on: March 27, 2017, 11:15:13 AM »

In the case of the few radios that are tolerant on lower voltages, I would agree but it seems most radios do not like the voltage supplied when the engine is off.

I  have never had that problem on HF or VHF/UHF. It is more about voltage stability than level as voltage declines. A battery is not a good regulated supply.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
N8AUC
Member

Posts: 317




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« Reply #19 on: March 28, 2017, 10:01:07 AM »

Ok on another note I do like W8JX idea of not using the booster junk. Raw battery feed is the best thing.

I also agree with not using a battery booster.
If you're not careful with one of those, it's too easy to over discharge a battery using one of those.
That will get expensive very quickly.
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K6JH
Member

Posts: 403




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« Reply #20 on: March 28, 2017, 12:18:29 PM »

Ok on another note I do like W8JX idea of not using the booster junk. Raw battery feed is the best thing.

I also agree with not using a battery booster.
If you're not careful with one of those, it's too easy to over discharge a battery using one of those.
That will get expensive very quickly.



The MFJ-4416B has a selectable cutoff of 9, 10 or 11V (default 10V). The intent being to avoid battery over-discharge damage. The other boosters I've seen have similar protection.

If you run the rig straight off the battery, are you careful to have a voltmeter attached, and never accidentally over-discharge your battery? There's risk that way too.

To me it boils down to this: I would try running directly off a battery first. But if a particular radio misbehaves even above 11V, I would consider a booster. But maybe a different radio is more practical.
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73
Jim K6JH
W4KYR
Member

Posts: 1598




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« Reply #21 on: March 28, 2017, 12:29:13 PM »

You can get two 7.2 volt batteries and use a dropping diode or two in order to give the radio  14 volts. A fully charged RC battery is 8.2 volts each...

Out of all the HF radios out there, the  SGC SG 2020 has the widest voltage tolerances, between 9 1/2 volts and 18 volts.


http://www.sgcworld.com/2020FAQ.html

Will the SG-2020 Operate with less than 12 Volts?
 1. For full spec compliance, the radio input voltage should be 13.6 to 18 VDC.
2. For full receive spec compliance with reduced transmit power, the radio input voltage should not be less than 10.5 VDC.
3. The radio will operate with reduced receive and transmit specs with an input voltage greater than 9.5 VDC.
4. The radio will cease to function at or below 9 VDC.
« Last Edit: March 28, 2017, 12:37:51 PM by W4KYR » Logged

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https://www.eham.net/ehamforum/smf/index.php/topic,111948.0.html

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W8JX
Member

Posts: 12081




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« Reply #22 on: March 28, 2017, 03:53:16 PM »


The MFJ-4416B has a selectable cutoff of 9, 10 or 11V (default 10V). The intent being to avoid battery over-discharge damage. The other boosters I've seen have similar protection.

10 volts is too low and will greatly shorten battery life. When a battery is rated for capacity on a 20 hr discharge rate, the cut off is 10.8 volts so real world even 11 volts is pushing it. 11.5 volts or so is more realist for better battery life.  That being said when rig does not work due to sagging voltage when using a cap to stabilize it too it is time to recharge or switch batteries, not use a battery booster. What many do not realize is that rigs power consumption increases with voltage (internal regulators use more power at 13.8 voltage than at 12.4 and a booster increases drain on battery because it uses power too so if you want max battery life/efficiency, you do not want a booster.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K6JH
Member

Posts: 403




Ignore
« Reply #23 on: March 28, 2017, 10:15:27 PM »


The MFJ-4416B has a selectable cutoff of 9, 10 or 11V (default 10V). The intent being to avoid battery over-discharge damage. The other boosters I've seen have similar protection.

10 volts is too low and will greatly shorten battery life. When a battery is rated for capacity on a 20 hr discharge rate, the cut off is 10.8 volts so real world even 11 volts is pushing it. 11.5 volts or so is more realist for better battery life.  That being said when rig does not work due to sagging voltage when using a cap to stabilize it too it is time to recharge or switch batteries, not use a battery booster. What many do not realize is that rigs power consumption increases with voltage (internal regulators use more power at 13.8 voltage than at 12.4 and a booster increases drain on battery because it uses power too so if you want max battery life/efficiency, you do not want a booster.

Yeah, I was thinking I would at least configure it for 11V, if not tweak it slightly higher. A low voltage cutoff really doesn't eliminate needing to monitor the battery voltage, does it? It's not something you want to run into very often for fear of damaging the battery. Like running a lithium battery down to the point where the protection circuit kicks off.

And if the rig doesn't work down to 11V, what good is it?
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73
Jim K6JH
K6SDW
Member

Posts: 80




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« Reply #24 on: March 30, 2017, 09:03:59 PM »

In the "olden" days as the supply voltage dropped many times the oscillators would start to lose lock and drift a bit. Ya can still hear this on SKN ....

73 all

k6sdw
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