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

[Loohan]

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

Yeah, well, must be something else wrong, then.
I did by the pricey DC/DC converter, PST-DC/2812-8 by PowerStream,
http://www.powerstream.com/dc-buck-boost.htm, and it does put out 12.16V any time I check, BUT it has not helped the problems at all. A total waste of money, as far as I can see. Here's an email thread I had with the seller about it: (and of course the sellers of the items I was trying to run claim that something's wrong with my power supply...)


(quote) This can't be explained by the DC converter. The main thing that blows capacitors is high voltage,
the other thing is putting a lot of AC current through them. Neither can be explained by the
house wiring or the DC converter.

We sell a lot of these converters to people that stabilize voltage in cars and busses, very noisy
conditions and we haven't had any complaints.



Dexter Ator wrote:

> That sounds plausible...
> I should say that the adapter behaved similarly without the buck booster when I had somewhat lower voltage in the walls. In fact, I had them replace a couple under warranty as they failed. This was the main reason I bought the buck booster.
>
> But I have also had similar problems with a mono amp designed for up to 18V:
> http://www.designnotes.com/Merchant2...gory_Code=auha
> Which blew its central capacitor directly on my system before the buck booster, probably at 13-14V. Then again, shortly after I plugged in the repaired unit with the buck booster, it blew its central capacitor. We're talking volcanic eruptions.
> These amps don't blow on a wall wart plugged into 120AC.
>
> So the buck booster does not seem to help at all with the problems that were obvious, and presumably doesn't help on any less-obvious problems that might or might not be there with other devices. I was expecting it would normalize my juice so things would run right. But I see no benefit.
>
> Mark W Lund, PhD wrote:
>
>> Wow this is a real stumper. Is it the laptop adapter that is getting hot?
>>
>> The only thing that I can think of is that sometimes when you have one switchmode power supply feeding
>> another they can drive each other crazy. For example the second converter is trying to draw constant power,
>> so it will increase its amp draw if the input voltage falls in order to keep at a constant wattage. But the
>> first one is trying to regulate to a constant voltage. So if the output voltage falls (say a disk drive kicks in) the
>> first converter will increase the voltage at the same time the second converter is trying to increase its input current.
>> This can set up oscillations, even chaotic oscillations.
>> This rarely happens when the dc converters are properly designed, but since you can't test every possible combination
>> it does happen.
>>
>> Best regards
>> mark
>>
>> Dexter Ator wrote:
>>
>>> Maybe you can help me. I bought a PST-DC/2812-8 several months ago because I have a couple thiings that won't run on my 12V home solar system. I thought this was due to fluctuating and excess voltage.
>>> But the items don't work much better through the PST-DC/2812-8. Although they run fine on a 12V wall adapter plugged into the grid, or a 12V jump-start pack.
>>>
>>> The PST-DC/2812-8 always says about 12.16V when I check it, which should be great.
>>>
>>> E.g. my auto laptop adapter (maybe I should have bought one from you instead of the PST-DC/2812- works dandy on my jump-start pack for hours on end, but on the PST-DC/2812-8 gets too warm and malfunctions after a 1/2 hour.
>>>
>>> __________ NOD32 2696 (20071130) Information __________
>>>
>>> This message was checked by NOD32 antivirus system.
>>> http://www.eset.com
>>>
>>>
>>>
>>
>
> __________ NOD32 2696 (20071130) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com
>
>
>

--
--------------------------------------------------------------
Mark W. Lund, PhD ** Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
(01)801-764-9060 ** Battery backup http://www.PowerStream.com ** Engineering, manufacturing, consulting

[icarus]

I'm probably too far from the beginning of this thread to understand what the ultimate problem was, (and not smart enough to boot!) but,

We had a bit a problem with our old fashioned 3 watt bag cell phone. When it was connected to the DC wiring of the building, the phone would beep for low voltage alarm, since the house batteries would be underload they would measure ~12.2-12-3 vdc at the end of the load wiring (long load wire). We solved it by adding a small 12vdc motorcycle battery that we plugged the phone into, and then plugged that battery into the building wiring. There was some concern that the 10ahr battery would pull down the 1600ah house batteries, but it has never been a problem.

Perhaps this will work.

Icarus

[mike95490]

The only other alternative I can fathaom is to get a 12 - 12 DC DC converter, from a major company that makes them [Vicor/CUI/YI/TYCO etc...]

Heres a sample Digi-Key Part Number 102-1257-ND
http://search.digikey.com/scripts/Dk...me=102-1257-ND
CONVERTER DC/DC 12V OUT 75W $99

These are commercial / laboratory quality usually, not made in a backyard, and with a wide input range, consistently give you good, clean output. Sometimes EBAY has things like this, but it's buyer beware there.

[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