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Some radical thinking
3 June 2023 | by Do we need those inline fuses between our radio and power supply, most if not all radios come with them but are they always needed? There was a time when I thought the more fusing the better and safer, but does it add to the safety or is it just redundant fusing? First off let me begin with, this is my own opinion and I do follow it whether you choose to or not it is absolutely up to you.
I was having an issue with my Icom 7610 cycling off and then back on again while transmitting . The issue was narrowed down to resistance within the cable from the power supply to the radio. I first replaced the poor terminal connections on my Astron power supply. The issue returned again it was then further determined that the guilty party was the inline fuse/fuse holder connection. I cut out both inline power cable fuses...OMG, you say?
Well, not really if (the big if) you have a power supply with very good built-in protection meaning over-voltage protection (crowbar), over-current protection (fold-back current protection), over-temperature shutdown and an internal AC fuse I believe you are good to go without inline DC fusing between power supply and your rig. Again in the background I hear "OMG, you did what"
If you don't need the inline protection then why is it there on most if not all rigs? The main reason is for mobile installations. The power supply is the car battery and there is no protection at the battery end for your rig. Also in the car, you have heat, cold, possible rodents, moving parts and so on around your power cables to your rig. Compared to home installation with a quality power supply your protection for a mobile installation is the inline fuses.
I do hear some saying "Wait what if there is an issue in my supply line from the power supply to the rig" This is true BUT keep the power cable as short as possible and if you have worries about overheating cables, moving parts or rodents then you have bigger issues than un-fused power cables. Having said that if something between the power supply to the radio power cable causes a sudden increase in current or voltage the power supply protection will quickly look after that.
Some who have a large rig such as the Icom 7610 or other manufacturers could be saying "there is no way this rig will be used as a mobile by the average ham but it has fused leads". My answer to that is the big 5 (Icom, Kenwood, Yaesu, Flex and Elecraft) have no idea what power supply you are going to use. Also, some may opt to use a deep cycle battery at home on a trickle charge or whatever.
After everything I have said about fuses I am not against them and as a matter of fact I have a Rigrunner fused rail and use it and I am thankful for it. I connect my external ATU, noise cancelling unit and SWR meter (for the light) to it.
Now if you have no issue with your supplied power to your radio and things are not acting up like they were with me then by all means keep the fused line but for me, some radical thinking cured the problem and some power supply understanding allows me to sleep at night knowing the radio is in good power supply hands.
8 Responses to “Some radical thinking”
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I have a friend’s Kenwood TS-570 on my repair bench that often loses RF output. This morning I found that the voltage drop across the in-line fuse holder was about one volt.
That along with another volt of drop at the rig’s power connector made for less than 11 VDC on the output collectors and 2/10 VDC loss of base bias. Kenwood calls for 13.8 VDC at the finals. I assume that oxidation and less than optimum pressure in the fuse holder may be the cause. The fuse holder has never been exposed to an out of doors environment. I have found that fuses can pass low level currents and act as a resistor at higher current levels. Once while installing a new Motorola Micor I found that the external fuse dropped the entire 13 VDC when the transmitter was keyed. A new fuse fixed the problem.
Good morning Larry and very nice to hear from you, I believe the main issue with the Icom inline fuse holder is the Sta-kon flag female connector that is used. They seem to loosen off over time. When this happens resistance is introduced and with that a voltage drop. I have tried to make the sta-kon gap smaller with needle nose pliers but over time it was not a good fix.
73,
Mike
VE9KK
Fuses induce resistance to power lines.
Good afternoon Bill and nice hearing from you, very true as all components within a circuit add some form of resistance. The issue with my Icom fuses I believe was the fuse holder. The setup for me over time increase in resistance and thus a voltage drop to the point when I transmitted the radio cycled off the on again.
Thanks for stopping by Bill and have a good what is left of the weekend.
73,
Mike
VE9KK
Recently I removed the fuse holder from my KX3 power supply line. I determined that it was the root cause of lower voltage than expected at the KX3.
Fuses in the power lines of DC powered rig are there to protect the wire from heat damage and fire, not the rig. They should be selected to open the circuit in the event of current flow that exceeds the temperature rise rating of the wire. Thus the wire should be chosen to have an ampacity and thermal / fire rating (and insulation voltage rating) exceeding the current demands of the rig.
I worked for many years in the industry (Mobile Radio) and have seen several instances of vehicles being burned to the ground due to faulty mobile radio installations and many instances of melted/deformed wires that were close to going up in smoke.
As far as Fixed stations are concerned, I agree that if the power supply has appropriate protection, no fuse is necessary. Again, if the wire is correctly sized.
73 and be safe.
Good morning Jeff thanks for taking the time to leave a comment on the post, yes the KX3 is a great radio. I had one up until a few years ago then I sold it for some ham bucks. For portable ops I would using a battery I would always used fused lines, but the KX3 has internal batteries and with those you are good to go. If I had to use inline fuses I would purchase some bolt on type were both the fuse and DC connections are bolted in place. You can actually pick up some small sturdy fuse holders that are like this. If you are at home and running from a quality power supply you are good to go.
73 Jeff and have fun with the KX3,
Mike
VE9KK
Good morning Ray and thanks for your input, yes in a mobile install for sure inline fuses are a must. With you being in the industry I would imagine you have your fair share of stories. I agree with the correct wire gauge and I would hope most hams have the basic understanding of current and wire size. But having said that I have seen some very knowledgeable people hold back for the sake of saving a few pennies. As for me I have 10 gauge between the power supply and radio as well as a short run.
73 and have a good week Ray,
Mike
VE9KK