REDUCING AMPERAGE for delicate electronics

[Loohan]

I'm not very knowledgeable about electronics, but have gotten the impression that it is unsafe to run some of them at too high a current (amperage) even if the voltage is right.

Is there any easy way to reduce some of the current from the system to say, 200 milliAmps or something?

Alternatively, I could run certain things off a separate, smaller battery, but then I would ideally want one that I can recharge directly off my home system without firing up an inverter.

As somewhat of an aside, I am curious if anyone knows how much difference there is (amperage-wise) between a standard automotive battery and the set of 6 Trojan 6V golf-cart batteries I have. I know that a deep-cycle battery has much fewer cranking amps than a car battery.

[BB.]

It depends on the electronics... Most electronics are designed to run from a constant voltage system (like a battery or DC power supply). The only limitation in current is a fuse to protect the wiring if a short occurs.

The problem with many electronics systems is that they don't like voltages out side of a narrow range (5-10% at most). Even batteries have a much larger range of operational voltages --especially if you include the voltage required to recharge the batteries (example--a 12 volt storage battery need around 15 maximum volts, and your electronics should be able to run all the way down to about 10.5 volts for when the battery is discharged and to allow for wiring voltage drop).

The amount of energy of a lead acid battery is approximately proportional to its weight.

However, the amount of energy you can pull out of a battery also depends on its design and intended usage. Going outside of its designed usage will dramatically reduce its recharging life.

A car battery is designed to supply high current--but only for a short amount of time. It will only, reliably, support about a 20% discharge cycle. A car battery is designed to give high current at "low weight"--i.e., cheaply.

A wet lead acid storage battery will not give high starting current, but will support a 50% discharge cycle reliably. Weight is typically not an issue and the lead plates are more solid to support deeper and more discharge/charge cycles.

Some AGM lead acid batteries can support 80% depth of discharge reliably.

All lead acid batteries will fail quickly if stored in a discharged state (except some AGMs). And all Lead Acid batteries will produce extremely high amounts of current if shorted and must be treated with high respect.

-Bill

[mike95490]

If you supply most appliances with the proper voltage, they take care of the rest.

A voltage surge will cause a proportional current surge though. Preventing this is easier done by controlling the voltage, not the available current.

[Wayne from NS Cana]

Yes, definitely control the VOLTAGE, and the current will take care of itself. You just have to make sure enough current is available for the biggest demand that the load will need and fuse it properly, in case there might be shorts.
Cheers
Wayne

[SolarJohn]

Stated another way:

Voltage is applied ACROSS a device.
Current flows THROUGH a device.
Current flow through a device is limited by that device's resistance.

As others have said: Control the voltage.

John

[Loohan]

Thanks for the replies.

My problem, at least one of them, is that I have a Mac that is very difficult to find a 12V adapter for. The one from Lind did not work at all. I finally found MacWizard's, who sells a dandy adapter for $40 that works excellent. For a month or so before it craps out. This has happened twice so far.

I talked to the tech engineer guy, who seemed quite sincere, and he told me it is probably that the current is too high. These units were designed for cars and planes. But, doesn't a car have about 12-14V just like my home?

Also, I have an audio amp designed for up to 15V DC that got real hot whenever I ran it, and eventually the main capacitor erupted like a volcano. Another guy who has the same unit says it's because the amperage is too high; he runs his on a little adapter that plugs into 110, and it does not get as hot, he says.

[BB.]

You might be better off getting a good 120 VAC Sine Wave inverter--Exeltech's are supposed to be very good lowered power units (reliable and efficient):

http://store.solar-electric.com/inverters.html

Regarding your 12 VDC solar system... I would check the voltage at where you connect your DC adapters... Check and make sure that the voltage is within specs--and not too high or too low (you might need to have your volt meter checked/calibrated--it would not be the first time here that strange things were reported only to find that the meter was bad--DVM's can look good and yet really be bad when you check your important voltages).

Second--it is possible that if you have heavy loads on your battery system--that rapid fluctuation in voltage is impressed onto the DC device (well pumps starting/stopping, Chargers causing ripple, etc.). With the correct meter (typically a DVM that does not read RMS), you can change the setting to "AC" and see how much ripple voltage there is...

There is one other issue that I can think of--it sounds strange, but you could have too good of wiring connection to your DC devices (large diameter wire and short run from the battery bank to the DC converter). What could be happening is when you apply power to the device--there is a huge surge of current which either directly stresses the capacitors and/or the fast inrush and a little bit of inductance causes the voltage to way overshoot 12 VDC--causing a short voltage spike which damages the converter.

Also, if you have ripple in your battery bank (charging/heavy cycling loads), with heavy cables it is possible that the input filter caps are trying to filter the battery bank voltage (heavy currents in caps).

Using a 10 amp fuse and 10' of 14-16 gauge wire may add enough resistance and "decouple" the input filter stage of the DC adapters from the battery bank. Twist the + and - leads (several turns every foot) to prevent other issues with radio interference--wrap excess cable in a "figure 8" pattern.

Low impedance between the battery bank and the DC converter is about as close as I can come to understanding the comment about "too much current".

Another question--are you equalizing your batteries when the DC converters are connected/operating? Equalization of storage batteries is typically at a higher voltage than the average car system would see (somewhere around 15.5 to 16.0 volts--might be higher than the typical car adapter is designed for). Making sure the adapter is disconnected from the battery bank when equalizing might help them to last longer.

It is all a guess--without seeing your application and having the right equipment--it will be difficult to diagnose with my keyboard.

Anyone else have any ideas?

-Bill

[crewzer]

Loohan,

Charging voltages for your "12 V" Trojan battery bank can range as high as ~14.8 V at ~77 F in absorb mode to ~15.5 V in EQ mode. As Bill has suggested, I suspect that these high voltages are the source of the problems you're seeing. The only "problem" with the big battery bank's capacity is that it can sustain these high voltages when powering a small load.

I'd suggest a DC-DC converter to regulate the battery bank's voltage range (~11 V under load to >15 V while charging) to a constant 12 V. Something like a "12 V" (~10 V to ~30 V in) to 12 V out model should work nicely. Take a look here for examples.

HTH,
Jim / crewzer.

[Wayne from NS Cana]

Yes, the voltage is quite a bit too high, or has very high ripple. The "main capacitor" should have been rated for at least 15 volts, probably 16 and normally will stand 10 or 20% over that without g erupting "like a volcano". If the voltage isn't too high, then there must be very high ripple in the supply, causing the capacitor to overheat from the continuous heavy charge /discharge cycles involved.
Not all capacitors are of equal quality, but as a test a few years ago, I subjected a couple of 6 VDC 20,000 MFD caps to 13.5 volts for an extended period. No problems resulted. Mind you I would never use them that way, this was just an experiment. The electrical leakage increased very slightly while subjected to the higher voltage, but returned to normal as the voltage dropped.
Just a note, many "wall warts" have a substantially higher "no load/low load" output voltage than claimed. It's not uncommon to see a 9 volt unit putting out 12, or a 12 volt unit delivering 16, or 18. I was rather shocked when I first saw that, but soon learned it was quite common with many manufacturers.
Wayne

[niel]

"I talked to the tech engineer guy, who seemed quite sincere, and he told me it is probably that the current is too high. These units were designed for cars and planes. But, doesn't a car have about 12-14V just like my home?

Also, I have an audio amp designed for up to 15V DC that got real hot whenever I ran it, and eventually the main capacitor erupted like a volcano."


i concur that you have higher voltages than you should have. that 'main capacitor' is usually an electrolytic and the standard rating would be 16v for it in your audio application. they can go bad on their own, but i suspect the voltage is at or exceeding this voltage. that voltage would be dangerously high for running any electronics as the electrolytic caps in them could litterally explode with too high of voltages or as mentioned ac ripple. you make no mention of how or with what you charge your batteries. if it is a standard automotive battery charger, these are unregulated and when the battery reaches a higher charge point the voltages are free to keep going up and can not only destroy the stuff you run from your batteries, but this can destroy the batteries themselves as the higher voltage does keep currents high to the battery and not just the items you are running from them.
you don't know much about electricity, but i suggest you learn some barebones basics and get a cheap digital voltmeter to see what kind of voltages are present. you don't want to destroy your stuff because of a lack of basic knowledge. the school of hard knocks is not always the best way to learn about stuff.