ALS-500 and batteries in trunk Vs long, thick power leads from engine battery

Discussion in 'Amateur Radio Amplifiers' started by W7JZE, May 18, 2018.

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  1. W7JZE

    W7JZE QRZ Lifetime Member #84 Life Member Platinum Subscriber QRZ Page

    I am currently, successfully running an Icom-7000 from the trunk of my 2011 Lincoln Towncar. Annotated pictures are on my QRZ page. Without pulling additional amps, from the engine battery, for a new ALS-500 installation, I can currently “modulate” the brightness of my headlights powering just the 100 watt Icom-7000. If I yak too long at night, watching the headlights dim as I speak, the red dashboard battery light will eventually come on as well :eek:.

    SOooo, I very much want to add an ALS-500 to my mobile station but feel that pulling an additional 40 or 60 amps from the engine battery, over dozens of feet of very thick cabling back to the trunk might seriously overload the car’s electrical capacity.

    I am instead considering adding two 80 AH sealed, deep cycle, 12 volt batteries in the trunk next to where the ALS-500 would be mounted. I would negative ground the two trunk batteries to the vehicle, like the ALS-500 would also be grounded. I do NOT intend to connect the trunk batteries’ positive (+) leads to the engine battery! I hope to isolate the large current draw, from the ALS-500, away from the vehicle’s electrical system.

    The ALS-500 manual strongly recommends NOT using trunk batteries, but if doing so anyway, it says that the positive (+) leads of the trunk batteries must connect to the engine battery which is the exact condition that I wish to avoid since I want to isolate the power draw to the ALS-500 away from my vehicle’s already (apparently) strained electrical system.

    Since I usually listen 90% and talk 10% (or less), I am thinking of keeping the trunk batteries “topped off” with a trickle charger powered though a 12v - 120v inverter.

    Ideas, please? Will my idea work, or am I off in the weeds somewhere?

    Thank you.

    Bill - W7JZE
  2. KV4PD

    KV4PD Ham Member QRZ Page

    W7JZE likes this.
  3. W7JZE

    W7JZE QRZ Lifetime Member #84 Life Member Platinum Subscriber QRZ Page

    You have exemplified my point exactly! I do NOT want to run very long, very thick cable for many dozens of feet (ALS-500 needs TWO separate 12vdc cable sets. 40 amps <peak> each).

    That is one reason why I want to figure out a safe way to power the ALS-500 from trunk mounted batteries right next to the ALS-500. Short cable run. 2 or 3 feet maximum. Negative ground batteries and ALS-500 to car body but do NOT connect trunk mounted batteries’ positive (+) terminals way up to the engine compartment.

    This is effectively a separate 12vdc system from the car’s 12vdc system.

    The other reason why I want to somehow safely power the ALS-500, in the trunk, from a 12vdc system in the trunk, separate from my car electrical system is that I do not believe that I can safely pull an additional 80 amps <peak> from my car’s electrical system without risking damage to it.

    Thank you for your feedback.

    I agree with your concern.

    I am just not sure if this type of isolated powering of the ALS-500 will work and if it does, is it safe? Ground loops? RF problems?

    That’s a lot of amps to pull, regardless from where they are supplied.

    Shorter runs of cable seem safer (and EASIER!).
    Last edited: May 18, 2018
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think it's a bad idea with two 80AH batteries. However if you already have the batteries, why not connect them up (even temporarily), try it, and see what happens?

    What I predict will happen is as soon as you start transmitting, they'll be drained very quickly and will be down at 11.5V within a couple of minutes; below that, the amp's relay will start chattering and you'll be off the air with the amplifier (although your rig should still work fine).

    I've bench tested ALS-500s before and they really want to see about 14 Vdc to work properly. At 12Vdc supply voltage, their output power falls off from 500W to 400W, and below that they really don't work.

    I'd try to find out why your headlights are dimming with only a 100W (presumably about a 20A load) transceiver. I've had 100W rigs in lots of different vehicles over the years and never, ever saw that happen. Sounds to me like there's a problem with the vehicle's electrical/charging system, possibly a single loose connection anywhere under the hood could do that.
  5. W7JZE

    W7JZE QRZ Lifetime Member #84 Life Member Platinum Subscriber QRZ Page

    Thanks, Steve...

    I hadn’t considered an existing problem with my car’s electrical system. I’ll look into that today. The modulation of the headlights’ brightness is most easily seen when on high-beam, with the A/C also running, and me yakking into the nighttime mic.

    I’ve read the ALS-500 manual a few times now and agree that the ALS-500 really, REALLY wants 14 or more volts. I was hoping that keeping the trunk mounted batteries topped off with a trickle charger when the car is running would keep them close to 13.8vdc, but maybe the only way to find that out is to just try it and see.

    I have other uses for two 80 amp hour batteries. Field day is coming up and I will again run a solar powered, portable, battery station and my four existing 35 amp hour batteries could be augmented with these larger units so that I don’t have to swap them out with the three solar chargers so often.

    Looks like I’m off to buy some big batteries and an ALS-500.

    Thank you for your feedback, Steve.

    Anyone else??
    Last edited: May 18, 2018
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I doubt they'll remain "topped off" with a trickle charger.

    Remember the AH rating for most batteries is based on a 20-hour discharge, so an "80AH" battery should be good for 4A over 20 hours. It will not be good for 80A over one hour, or 40A over two hours, etc. As such, IMO you'll be depleting them really quickly and to keep them "topped off" for intermittent duty at about 25-30A each, you may need a charge rate of 8A or more, which isn't really a "trickle."

    I think the 2011 Town Car has a 4.6L V-8 with a 135A alternator; I'd "think" if both the battery and the alternator/regulator are okay, you shouldn't see any dimming with a 20A load like a 100W rig. Have the system checked and I suspect they'll find something wrong.
    W7JZE likes this.
  7. KV6O

    KV6O Ham Member QRZ Page

    Alternately (alternator pun right there), get yourself a rear engine car, then the alternator is in the trunk already.

    Your welcome.
    N8VIL and W7JZE like this.
  8. W7JZE

    W7JZE QRZ Lifetime Member #84 Life Member Platinum Subscriber QRZ Page

    Steve (WIK)... just spoke to an “Auto Electric Specialist” locally and he agrees that the 140 amp stock alternator on the Towncar should run the 23 amp pull from the barefoot Icom-7000 without “modulating” the high-beams when I speak into the mic. I’ll have the car’s electrical system checked with him next week.

    Also: interestingly enough, when I explained that I was an amateur radio guy looking to add a “Radio Amplifier” in my trunk that could pull as much as 80 amps, he interrupted me and suggested that I only needed to add “additional battery capacity”, not an upgraded alternator. And... that the additional battery should be in the trunk close to the power draw. His idea, before I even mentioned it!

    He also mentioned lots of grounding needed for the trunk battery and the amp to the car body.

    KV4PD: Thanks for your idea of the battery isolator. The Auto Electrical Specialist also suggested exactly that! He said that would allow just a single, smaller gauge positive (+) wire (did he say 10 ga?? Not sure), from the isolator (up front???), back to the trunk battery, to keep the trunk battery charged.

    MISC: hard to get this all explained, both ways over the telephone with the “Auto Electrical Specialist”, but it seems I’m on the right track with a trunk battery or batteries. I’ll meet him in person next week and hash out the details and hopefully a schematic.

    Thank you all for your input and ideas.

    If any of you know of a successful trunk mounted battery installation to power an RF amplifier, please chime in.

    Thanks :)
    Last edited: May 18, 2018
  9. K6BSU

    K6BSU Ham Member QRZ Page

    My '55 Chevy mobile rig had only a modest 150W (AM) amp in the trunk. The Rx and Tx were home-brew and small enough to fit in the glove box with cover removed. There was room under the hood for a second 12V battery, which guaranteed I would not run out of battery power.

    For power cables to the trunk, I didn't have any heavy wire, so I ran 4 (I think) 14 ga solid house wires for the + and -.
    W7JZE likes this.
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Actually, everything you just wrote made a lot of sense.

    Charging from the vehicle's charging system via an isolator and sufficiently heavy gauge copper wire (#10 might do it, I'd probably use #8) to keep the "trunk battery" charged sounds like a great idea: The trunk battery could pull 30A through that and have enough juice left to actually keep the battery maintained at or above 12V.

    So, the "I don't want anything connected to my main battery" technique probably wouldn't work well at all -- but this alternative method should.

    I'd still have the system checked out, as it sounds like something isn't working properly.
    W7JZE likes this.

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