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Author Topic: Portable Solar/Battery Setup  (Read 1507 times)
KF5QJV
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Posts: 6




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« on: July 26, 2012, 01:33:41 PM »

Hello Experts,

I want to develop a portable system around my FT-857 and am needing some validation.  The components I have in mind are:

Lead Acid Battery, probably something like a Universal Battery UB12120
PowerFilm F15-600 (10W) or F15-1200 (20W) foldable solar array
Charge controller, leaning toward the Morningstar SG-4 SunGuard (4.5A)
Watts Up meter/monitor
PowerPole connections throughout

So, I've seen a lot of postings and videos here/there about hooking up similar components.  It appears that the solar panel connects to the charge controller, which then connects to the battery.  Then, the radio connects to the battery (with the optional Watts Up monitor in between).  A lot of folks warn against attaching the solar panel/charge controller directly to the radio, that it must go directly to the battery with the radio also connected to the battery, so the radio is being powered from the battery and not directly from the panel.  However, I'm not sure I understand how the various safety risks are mitigated when both the panel and radio are sharing the same battery terminals.

Since the UB12120 has only a single pair of F2-style terminals, I'm wondering if I can use a PowerPole splitter as a "hub" between the battery, charge controller and Watts Up monitor.  The radio would be connected to the other side of the monitor, while the solar panel would connect to the other side of the charge controller.  Electrically, this doesn't seem any different than sharing the battery terminals between the solar panel and the radio (as in the previous description), but it cleans up the connectivity quite a bit for me.  Plus, using PowerWerx's 4-way PowerPole splitter would accommodate an extra connection for a female cigarette lighter socket for auxiliary use (e.g., charging my HT).

My other question relates to fuses.  The power cable for the FT-857 has an inline 25 amp fuse assembly.  Is this sufficient, or should additional fuses be added between other components in this system?  If so, where and of what amperage?

I hope my descriptions and questions make sense, and any help/comments would be greatly appreciated!

Rob
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K0IZ
Member

Posts: 737




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« Reply #1 on: July 26, 2012, 01:54:50 PM »

Rob, I will comment on a portion of your questions.

Your selected battery is 12ah, which should be a adequate for modest amount of transmitting.  Probably good compromise between watts and weight.
The solar cell -600 is rated at .6a.  Really isn't 10watts, since it will be connected to a 12V battery.  Solar cells are constant current devices, so this panel would deliver .6a even into direct short.  So your power (full sun) would be about 12V x .6a = 7.2 watts.  Double for the -1200 panel.  Assuming that you might get 6 hours or so of sun under some conditions, the -1200 would have a better chance of keeping battery up (6hrs x 1.2a) = 7.2ahrs.  Recharging battery is not 100% efficient, maybe 3/4 or so.  So the 7.2ahrs would replace perhaps 5.5 or so ahr in battery.   

Open circuit voltage of a solar panel can be as high as 20 or 21 volts.  That is probably why you were given advice not to connect panel directly to radio.  If you did so, and battery became disconnected, your radio would see that 20 or 21 volts.  By connecting panel to battery, and then battery to radio, that risk is gone.  Obviously for same reason you would NEVER want to operate the radio with just the solar panel.

You may not need the charge controller.  Even the -1200 panel will crank out only 1.2a, which is 1/10 of battery capacity.  So relatively little danger of grossly overcharging battery.  With -600, even less likely.  Without controller you would not want to let battery be on charge for extended periods without using the battery some.

There are push-on spade terminals that will take two connections.  Also some favors of the 12120 battery have twin spades on each terminal.

Have fun.   John.
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KF5QJV
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Posts: 6




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« Reply #2 on: July 26, 2012, 02:46:12 PM »

Thanks John.  I guess I'm still not seeing how to avoid connecting the panel directly to the radio.  If the panel and the radio share the same battery terminals, how am I not still faced with that "high-voltage" risk from the panel to the radio?  It sounds like the battery is somehow "protecting" the radio, but I'm having trouble understanding the theory behind it.

Rob
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NA0AA
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Posts: 1042




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« Reply #3 on: July 26, 2012, 08:43:28 PM »

Try this:

Connect your volt meter to the panel in the sun, see the high voltage - this is open-circuit, or without a load on it. 

Connect a 20 watt, 20 ohm resistor across the terminals, now measure voltage - you are putting, at 13.8 volts, a 10 watt load on the panel.

Check voltage - this is roughly what your radio draws on receive.

That would be a good way to estimate.

Also, you can connect the battery and check voltage - the battery acts as a load - and as long as you don't let the battery achieve full charge or more - and with a volt monitor you are safe - the 857 can take I think up to around 14.5 volts, at which point your battery will start to smoke...OK, maybe not, but that would be a max you would want.

I think you are safe.
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KA4POL
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Posts: 1981




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« Reply #4 on: July 27, 2012, 02:47:41 AM »

An important value to check is the internal resistance of a battery. Your rig has a max specification of 22 A. The battery got 22 Milliohm internal resistance. This makes you loose about .5 V max which you need to subtract from your lower working margin of 13.8 V +/- 15%. The real solar batteries have an improved deep cycle performance.
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K0IZ
Member

Posts: 737




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« Reply #5 on: July 27, 2012, 07:08:38 AM »

The battery voltage will vary with charge in it, from below 12 volts to maybe 14.2 or so.  When you connect a constant current source (ie solar panel) to the battery, the battery will attempt to absorb as much current as the source can deliver, and as battery charge approaches 100%, battery voltage will rise to the 14.xx.  Assuming no radio load, the battery thus is pulling down the solar voltage to the battery voltage.  That "protects" the radio.  When battery reaches full charge, it will still attempt to absorb solar current, and begin to "cook" the battery.  No good, thus at that point a controller would be shutting off solar current.

I think in your case the main risk is that when hooking up DC cables, you would accidentally make the radio and solar connections before connecting the battery terminals.  That could easily damage radio, even when radio is "off" since most modern radios (like TV's, etc) are internally powered whenever DC is applied to radio.

I seem to recall that there are devices being sold (and maybe some construction articles) on a voltage "crowbar", which clamps down on voltage if it exceeds a certain value.  Placing such a device across the radio DC terminals would provide protection.  With battery in circuit, might have to add fuse between crowbar and battery to prevent crowbar from shorting battery.  I really don't have familiarity with crowbars, but maybe someone else on eham could help.

John.
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KA4POL
Member

Posts: 1981




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« Reply #6 on: July 27, 2012, 07:29:18 AM »

A transient voltage protection diode with a fuse will do the same. And a switch to really take the rig off line are recommended.
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KF5QJV
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Posts: 6




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« Reply #7 on: July 27, 2012, 12:25:41 PM »

This is all great feedback, and I really appreciate everyone for taking the time to respond!  I think it's starting to become a little clearer now.  :-)

Rob
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