View Full Version : Need to Upgrade Mobile Fusing
I use an Icom IC-7000 and an N8XJK battery booster in my car. I've been enjoying PSK-31 while stationary lately. However, twice so far, if my transmission lasts more than about a minute, one of my 30-amp powerline fuses will snap. It's frustrating, because by the time I'm back on the air, the person I had the QSO with is gone. The battery booster appears to pull 40 amps during heavy use, according to the specs, while the IC-7000 is fused for 30 amps.
Therefore, I want to know whether this is a good approach. I can replace the fuses at the battery with 40-amp fuses. The power cable can handle the load. Then, I would add 30-amp fuses to both power leads between the battery booster and the radio. It makes sense to me, but I want to be sure I'm not fooling myself.
WB2WIK
03-31-2011, 11:01 PM
Why do you use the booster?
Although it raises the voltage, it drains the battery faster than if you didn't use it.
When I am stationary, with the engine off, the voltage is lower, and the radio transmits at a maximum of about 60 to 70 watts. With the booster, I can transmit at maximum power. As for the battery, it's a Deep Cycle, and I have operated for several hours without any problems.
WB2WIK
03-31-2011, 11:41 PM
What other load do you have on it besides the IC-7000? The 7000 by itself shouldn't draw more than 20A peak or so. If the booster is blowing a 30A fuse, either your load is much more than the IC-7000 or the booster is very inefficient.
I can use my FT-857D in the car for several hours with the engine not running and it runs a full 100W output the whole time. I do this quite often, actually. SSB or PSK31 duty cycle is 50% at most, with SSB generally being much less, so average current drain is 10A or less when transmitting and about 1A when receiving. What other stuff are you using besides the Icom?
I only have the IC-7000, battery booster, and Signalink USB running off the battery. I never had any fuse problems until using PSK31. Sometimes, I transmit at more than 50 watts, to reach a DX station, while ensuring the ALC meter is at zero. That's when the fuse snapped. The booster indicates it pulls up to 40 amps at full load, so I am pushing it passed my 30 amp fuses.
This is why I'm asking about my idea of using 40 amp fuses at the battery, and 30 amps at the radio.
WB2WIK
03-31-2011, 11:54 PM
To me it sounds like something is seriously wrong with the booster. At 50W output from the 7000, you should be drawing no more than 14A, period. If the booster draws in excess of 30A to provide 14A to your rig, the booster's efficiency is terrible. The Signalink draws almost no power at all (way under 1A).
Rather than using 40A fuses at the battery, I'd investigate why it's drawing so much current. The booster drawing 30A to provide 14A to your rig means it's dissipating a ton of power and will eventually fail.
Thank you. You're making a valid point, and I'll check the booster. I was running around 80 watts when the fuse snapped, and that was after about a minute of steady transmit. I recall that the temperature meter of the radio was at more than 50%, and the booster's heat sink was feeling hot. I will be sure to back off on the power. However, I will probably try my fuse upgrade idea, to prevent going off the air again.
WB2WIK
04-01-2011, 12:29 AM
The heat you feel in the booster is just "wasted energy."
This is why I don't use stuff like that. It may keep your rig happier temporarily, but in reality it's just draining your battery faster. Not worried that will hurt the battery, I doubt it will. It's just a waste of power.
If I need more power in my vehicle for mobile operation, rather than going to "deep cycle," I go to a bigger battery with higher capacity. Most cars and trucks can accommodate a higher capacity battery than the one they come with. I replaced the one in my van with one nearly 50% higher capacity and although it was "taller," it fit the mounting plate and brackets just fine.
If heat is wasted energy, then the IC-7000, and many other radios, waste a lot of it. However, that's the price for performance.
As I recall, the battery I had installed is rated at something like 90Ah. It's designed for operation like this, versus simply starting the car. It works great. If I've been operating for several hours, I run the engine for a bit, to ensure the battery is adequately charged. I'm not worried about draining it, and it has a 10-year replacement warranty.
How long are EACH of the leads from the booster to the battery?
Do you run the negative (bad idea) and positive of the booster directly to the battery posts?
What is the voltage at the input of the booster?
Do you have fuses on the radio side of the booster?
How long are the leads to the radio from the booster?
It could be something else besides a bad booster.
KB9DT
04-01-2011, 08:39 AM
The input power is the output power plus the booster loss.
With an output of 13 volts at 20amps, or 260 watts, the input power would be close to 290 watts (assume a 90% eff boost). If the input voltage to the converter dropped to 10 volts under load, the input current would be 29 amps.
Even with 10 volts and 30 amp fuses, 100 watts PEP SSB should be OK because of the low average power....PSK would be 100%, but at lower power, so it should work too.
Check the voltage on the input side of the converter. Do the fuses get warm? If they do the contacts at the holder may be bad.
How long are EACH of the leads from the booster to the battery?
Do you run the negative (bad idea) and positive of the booster directly to the battery posts?
What is the voltage at the input of the booster?
Do you have fuses on the radio side of the booster?
How long are the leads to the radio from the booster?
It could be something else besides a bad booster.
Both the positive and negative leads are from the battery, and are about 10 feet long. Pros and cons on either wiring method can be found throughout the web, however I have found more pros about connecting both to the battery. The voltage input to the booster is about 12.5v with the engine off, and 14.1v with the engine on. If the engine is on, I typically have the booster in BYPASS mode. I installed 30amp fuses on each lead from the booster to the radio, and the leads are about 18" long. I plan to replace the 30 amp fuses at the battery with 40 amps.
The input power is the output power plus the booster loss.
With an output of 13 volts at 20amps, or 260 watts, the input power would be close to 290 watts (assume a 90% eff boost). If the input voltage to the converter dropped to 10 volts under load, the input current would be 29 amps.
Even with 10 volts and 30 amp fuses, 100 watts PEP SSB should be OK because of the low average power....PSK would be 100%, but at lower power, so it should work too.
Check the voltage on the input side of the converter. Do the fuses get warm? If they do the contacts at the holder may be bad.
Thank you. I understand your logic. However, when the fuse snapped, I was running about 80 watts on PSK for about a minute. The fuse holder was very warm. When transmitting at 50 watts or less, the fuse holders remain cool. The fuse holders at the battery are the stock Icom blade fuse holders, and I've been told they are not ideal.
WB2WIK
04-01-2011, 04:11 PM
Thank you. I understand your logic. However, when the fuse snapped, I was running about 80 watts on PSK for about a minute. The fuse holder was very warm.
That's pretty interesting, right there. Possibly the fuse/fuseholder and/or its connections aren't up to the task.
That's pretty interesting, right there. Possibly the fuse/fuseholder and/or its connections aren't up to the task.
I agree. I'm tracking down a source for better connectors; ones that are not pre-wired, but have terminals for existing cables. It's possible that my connectors could not handle the current for 40 amp fuses, if I go that route.
The Icom uses ATO fuses, and almost all after market holders have a loop wire that requires you to use butt splices. However, you can use Power Pole connectors for a fuse holder. It is a bit difficult to get the fuse between the spring and the contact, but once done they're reliable.
Personally, I use Maxi fuses, and Littelfuse's MAB1 holders. The connection utilizes #10 screws, and I've never had one fail for any reason.
Tom and I are at odds about the direct battery connection, and the reason is simply the capacity of the accessory ground connection. You're no doubt okay if the power level is reasonable, but if you run an amplifier (≈75 to 90 amps peak), the extra draw puts a lot of stress on this wire. I have actually seen cases where the wire acted like a fusible link, and that's the last thing you want it to become.
Hi Alan,
Thank you! Your description of the power leads fusing together makes the argument of having the ground wire separate from the postive very valid. I'll remember that, if I ever use an amplifier.
Regarding the Littelfuse MAB1 holders, is this the kind you're using? http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=655422&k=mab1
If it is, what do you use for terminals, and how do you insulate the contacts? If it's NOT the one you use, would you post a link to what you have?
KB9DT
04-01-2011, 08:29 PM
I've had good luck with AGU fuses for 12 vdc. Use them in the car and my travel trailer. Look for a place that sells high power car audio.
A couple of things.
First, AGU fuses are on the way out. Yes, you can still buy them, and perhaps for some time in the future. Sooner or later, they'll get expensive. And.... ATO, mini fuses, and maxi fuses, have a better predictable hysteresis over their temperature range than 3AG, 5AG, or any of the round-style fuses. This is why the automobile manufacturers have switched over to them. In fact, most auto OEM high current applications, are not using JCASE fuses for the same reason.
Finding lugs for large-sized wire (>#8) which fit the MAB1 fuse holders can be a lesson in frustration! Fastenal, Digikey, and Mouser do carry them, yet they're hard to find. The ones I use are made by Bussmann, and I found them at the local Fastenal store.
WA9SVD
04-03-2011, 03:21 PM
With all due respect, isn't one of the advantages of PSK31 the ability to make contacts at low power? Needing 100, or even 60-80 Watts seems a bit excessive.
Reduce the power (even as an experiment) to 20-30 Watts and see how the system works.
Remember, PSK31 is actually a 100% duty cycle mode, and is running full power while in transmit. SSB or CW will typically have only a 20-40% duty cycle.
I agree about the PSK-31 power. However, when operating as a mobile station, I frequently have trouble with DX stations copying my signal. I sometimes raise my power, to make the contact, and it doesn't always help.
I spoke with the N8XJK battery booster manufacturer, and was told that the booster has its own 40 amp fuse inside. Further, if I have a fuse from the booster to my radio (which I now do), I should probably not use a fuse between the battery and the booster. I'm not sure whether this is a good idea, because it's usually the best practice to have the fuses at the battery. However, if fuses ARE kept at the battery, they probably should be 40 amps, because that's what the booster can pull. This was the basis of my original question.
Hi Alan,
Thank you! Your description of the power leads fusing together makes the argument of having the ground wire separate from the postive very valid. I'll remember that, if I ever use an amplifier.
Regarding the Littelfuse MAB1 holders, is this the kind you're using? http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=655422&k=mab1
If it is, what do you use for terminals, and how do you insulate the contacts? If it's NOT the one you use, would you post a link to what you have?
http://www.w8ji.com/mobile_ground.htm
and this link
http://www.fcs.org.uk/my%20files/fcs_pdfs/codesofpractice/08-05-12%20fcs%201362%20final.pdf
I can't understand why people want to give advice that is potentially harmful to gear and the vehicle. If they don't understand the system, they shouldn't give any advice.
Anyone at odds with me about negative lead fusing and negative lead termination is also at odds with the new European standard on negative leads. Europe has a directive that old installations done with the negative lead to the battery result in fire and equipment hazards. The new directive is old systems that were grounded to the battery should be changed to a chassis connection, and the negative lead fuse removed and a direct connection used from the gear to the chassis. This is for equipment with a ground path.
Running the negative lead to the battery post for accessories or accessory devices that are grounded or have a ground path is very clearly dumb-headed engineering. As for a typical ground wire from battery to chassis acting like a fuse for amplifier or inverter loads and opening, good luck with that myth!!! Fusing current of a number 10 copper wire is 330 amperes. Most battery to chassis grounds are around number 8. I run my 3000 watt inverter through a small fuse link of number 12 wire, on the HOT lead.
For those people interested, here are the problems with grounding to the battery post:
1.) If the gear has a ground path from the equipment to the vehicle chassis, that ground path becomes part of the battery ground. If anything ever opens from the battery to vehicle chassis ALL of the vehicle negative lead ground currents will flow through the gear. This causes ground loops that can put noise into the equipment, or can damage the equipment or overheat wiring. The negative fuse does NOT protect the equipment hazard, unless the negative fuse is sized for the smallest conductor leaving the accessory device to the vehicle chassis. That would be key jack or microphone sized wiring in most radios, so you would need a one or two amp negative fuse.
2.) If the battery negative should open, the equipment path becomes the full ground. Current through the device can be 100's or 1000's of amperes until the fuse blows, and the path can be through foil traces and semiconductors. A positive to chassis short can drive the negative post up above chassis even if it has a good connection.
3.) The negative lead fuse adds voltage drop even when good, and the small but finite resistance of a good system diverts currents through the other leads from the radio that are grounded.
By grounding to the chassis, less noise is induced in the equipment or the vehicle's system. Also any possibility of a fault powering the negative lead, or flowing through the radio's PC boards or external connections like antenna leads or speaker leads, is greatly reduced.
So here are the rules people with common sense would follow:
1.) If the accessory equipment is designed to be fully ground independent with no negative lead to case or external connections, it can run to the battery negative post provided that lead is fused.
2.) If the accessory equipment has a common ground to external ports or the cabinet from the negative lead, the negative lead should be grounded to the vehicle chassis without a fuse. If it is a really heavy draw, like hundreds of amperes, it would pay to improve the negative post to chassis ground and ground up near (but not on) that ground.
Nothing else makes sense.
73 Tom
Hi Tom,
Thank you for posting that information, and the link to the diagrams and PDF. In the PDF, at the top of page 31, it refers to making the negative connection to the frame as close as possible to where the negative battery terminal connects to the frame. In my case, I could simply move the negative wire from the battery to the frame. However, is it best practice to keep the positive and negative wires separated, or can they still be twin lead? I didn't find anything in the PDF about that, so far.
Tom while I agree with your assessment, the automobile manufacturers don't. For example, here's is GM guide: http://service.gm.com/techlineinfo/radio.html Ford's, Chrysler's, and about 20 others are virtually the same, including every EU auto maker.
I do understand the issue you present, about equipment grounds not being floated in amateur radio gear. And even the ramifications of a failure in the battery's accessory ground. I've only seen that happen twice, and both times when the starter ground failed.
There is another issue too (I'm not sure if you're the one who brought it up), about using the chassis (seat bolt?) as a ground return. Doing so will play havoc with the vehicle's electronics. This is the main reason for the wiring guides in the first place.
A lot of the possibilities boil down to improper maintenance, and extremely poor wiring practices. Some of the photos sent to me for inclusion in my web site's photo gallery are so poorly done, it's a wonder they haven't gone up in flames.
WA7PRC
04-04-2011, 09:03 PM
If the accessory equipment has a common ground to external ports or the cabinet from the negative lead, the negative lead should be grounded to the vehicle chassis without a fuse.
This can't be emphasized enough. As a note, with modern equipment where the negative is common to its chassis, just mounting the rig to the vehicle may ensure the negative is returned to the vehicle chassis (and make any negative wiring to battery immaterial). But, when I install a rig, I don't bet on it. Just recently, I installed my TS130S into my pickup. My ground is short and to the nearest vehicle chassis location.
Bryan, one of the issues is voltage drop, as I mentioned before. While it might not be insignificant, there is another issue at hand.
The various accessory grounds throughout the average, modern vehicle may indeed seem haphazard, but I can assure you they are not. Commonly supplied devices, use common grounds. This is done to reduce the possibilities of a ground loop causing problems with the myriad of on-board devices. If you impress a load through the steel body of the vehicle, it is likely to cause a differential between grounding points. You personally might not ever have a problem, but you're not exempt.
Now that OBDII-EOBD has become the de facto standard, it is even more important that we follow the wiring recommendations of the manufactures. I won't argue about the efficacy of direct or indirect battery ground wiring. However, I will argue about using the chassis for a ground return. If you have a late model vehicle equipped with OBDII-EOBD, you might be writing error codes you don't know about until something fails under warranty.
As I said above, to each his own. And, you take your chances.
WA7PRC
04-05-2011, 04:27 AM
Bryan, one of the issues is voltage drop, as I mentioned before. While it might not be insignificant, there is another issue at hand. [snip]
I wasn't looking for approval. Suffice to say that I've investigated this and my installation (for my application) is quite sound, again.
finit