Need to Upgrade Mobile Fusing

Discussion in 'Mobile Radio Systems' started by NO6O, Mar 31, 2011.

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  1. KB9DT

    KB9DT Platinum Subscriber Platinum Subscriber QRZ Page

    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.
  2. NO6O

    NO6O Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    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.
  3. NO6O

    NO6O Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    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.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That's pretty interesting, right there. Possibly the fuse/fuseholder and/or its connections aren't up to the task.
  5. NO6O

    NO6O Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    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.
  6. K0BG

    K0BG Ham Member QRZ Page

    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.
  7. NO6O

    NO6O Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    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?

    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?
  8. KB9DT

    KB9DT Platinum Subscriber Platinum Subscriber QRZ Page

    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.
  9. K0BG

    K0BG Ham Member QRZ Page

    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.
  10. WA9SVD

    WA9SVD Ham Member QRZ Page

    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.
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