REDUCING AMPERAGE for delicate electronics

System · June 2007

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. · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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.

System2 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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

System2 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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. · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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.

System2 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

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 · June 2007

Re: REDUCING AMPERAGE for delicate electronics

"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.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Thanks again for the replies.

Right now I'm in a weird situation: a couple days ago I noticed that my system has low voltage, around 12V.

We have had a lot of overcast weather lately, so I don't know if that's the whole problem. I strongly suspect that my MPPT 200 charge controller has either gone bad again or needs to be recalibrated. It went bad last year, and it took weeks to get it serviced.
The instructions say to check the float voltage adjustment (which by default is supposed to be 14.1V) by hooking it up to a panel and battery, but they don't specify whether it should be in the sun at the time. I presume it does, so I am twiddling my fingers until the sun comes out.
It may be that the problem with the latest "fixed" adapter I just tried Friday is low voltage this time, except that it's behaving the same way as it was 6 weeks ago when my voltage was normal.

I have 2 80-watt panels, one supposedly puts out 14v, the other 18v, the MPPT 200, and those 6 batteries. No particular load cycles on the system except when I run the cheapo inverter to run the Apple adapter, which I only do when the other isn't working.

BB, I can't afford a fancy inverter at this time, but I bookmarked it.
I have 10 awg wire running maybe 15-17' from the batteries to an outlet, then ~5' of 14 or 16 awg cord running to the outlet the adapter plugs into. So maybe you're right about low impedance.
I have 2 non-digital voltmeters. One claims I have 10V, the other a hair under 12V. The system does not seem to be charging at all, despite the fact that I'm only running the wireless LAN radio today (very negligeable draw).
It is quite overcast, but still...
I have in recent years purchased a cheap DVM (Velleman) which stopped working after a couple months, and another non-digital one, which did likewise. Next time, I'll hang on to the warranty paperwork.

I've never heard of equalizing batteries.

Crewzer, interesting link. Not dirt cheap, either, but may solve all problems of this sort. I see they even have a "reliable" adapter for my Mac at
http://www.powerstream.com/ADC--Apple.htm

Anyway, thanks for the help, guys. I have more of a clue now.
I'm thinking of investing in a PST-DC/2812-8
( http://www.powerstream.com/dc-buck-boost.htm ) Buck-Boost DC-DC converter. Am I on the right track?

mike95490 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Loohan wrote:

Thanks again for the replies.

Right now I'm in a weird situation: a couple days ago I noticed that my system has low voltage, around 12V.

We have had a lot of overcast weather lately, so I don't know if that's the whole problem. I strongly suspect that my MPPT 200 charge controller has either gone bad again or needs to be recalibrated. It went bad last year, and it took weeks to get it serviced.

( http://www.powerstream.com/dc-buck-boost.htm ) Buck-Boost DC-DC converter. Am I on the right track?

re Buck/boost - forget it till you've corrected your charging problem

Only 10 / 12V at the batteries. Sounds like they are not charging. On an emergency basis, try removing your charge controller, and connect the PV panels directly to the batteries and see if they charge.
Or call a competent PV electrictian.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Overcast weather today, as well as "lately" = no, or practically no charge available to go to the batteries. There may be no technical problems at all with your charging system, just a lack of full days of full sun to charge your batteries.
Overcast days will result in basically no charge going into your batteries, small load or no load.
Your batteries must be recharged fully, and fully means fully, otherwise they will be ruined.
Read up on equalizing batteries and also read up on the characteristics of the solar panels. There's lots of real good info right here on this site, you just have to dig for it. By the way, the info you will find on this site, unlike many other similar sites, is correct and without "old wives tales" and folklore.
Good luck
Wayne

BB. · July 2007

Re: REDUCING AMPERAGE for delicate electronics

But I have a feeling there are a lot of "old husband tales" around here. :roll:

If you have flooded cell lead acid batteries, you do need to check the water and equalize them--usually once or twice a month.

Find the name and model of the batteries and go search on the web for maintenance instructions and/or post the information here and somebody can find the links/information that you will need.

There is one fairly common battery technology that does not need equalization--Sealed Lead Acid. Gell Cells, Valve Regulated or AGM's are typical of this type of sealed battery.

Next, don't worry about the wiring--sounds like it is perfectly OK for 5-10 amps (you have a fuse near the battery to protect against shorts--right???).

Next, you do need a good. calibrated, and accurate meter--As well as a good (temperature compensated) hydrometer (measures the density of the cell electrolyte/acid--assuming this is flooded cell).

If you are really running the battery down and not getting it properly (and quickly) recharged--there is a very good chance that you are quickly running out the life of the battery bank.

It sounds like you may have grid tie power there too--Do you have a good AC Battery charger that you can connect to the battery bank? If not--somebody can recommend one based on your needs (size of battery bank and load per day you usually consume).

And a good couple hundred watt inverter might be cheaper than replacing all of those DC MAC converters (and about the same price as a DC to DC converter too). Plus the inverter can be put to all sorts of other emergency uses (lights, radios, etc.)

-Bill

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Thanks again for the replies.

The sun has come out some, and the system seems to be charging. I should say that normally my bank stays topped off a lot of the time, as I don't run much on it, and it's usually sunny. There's an LED on the controller that supposedly only comes on when the batteries are above 14V, and it usually stays on several hours a day while excess juice gets wasted.
I was on the verge of checking my float voltage adjustment, when I got a warning that my Mac was on reserve power, so I turned on the inverter to charge it. Soon as that's done, I'll check the other.

I checked what Trojan has to say (I have Trojan wet cells) at http://www.trojan-battery.com/Tech-Support/BatteryMaintenance/Equalizing.aspx

"Many experts recommend that batteries be equalized periodically, ranging anywhere from once a month to once or twice per year. However, Trojan only recommends equalizing when low or wide ranging specific gravity (± .015) are detected after fully charging a battery."

Whatever that means. Presently all I have is an automotive turkey-baster. It has FAIR, POOR, etc. and numbers like 1225, etc. And I haven't used that in a long time. Maybe later today I'll check my batteries.
I forgot to mention I also have an automotive battery tester that seems to have an accurate, though not precise (the dial only has marks at 1/2V increments), voltmeter.

I do not have grid here. And the few things I run are almost all 12V, so I did order that buck-booster.
I do have a genny I fire up when I need to run power tools.

crewzer · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Here's a link to precision hydrometers: http://store.solar-electric.com/baacma.html

The EZ-Red SP101 appears to be fairly popular: http://www.sjdiscounttools.com/ezrsp101.html

HTH,
Jim / crewzer

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Dang, my last reply of several days ago didn't make it to this forum, and is no longer to be found. I shall try to reconstruct part of it.

Someone (another missing post?) said that I should have a max of 1 aH of battery for each watt of PV, and that I have 675(?) aH on my 160-watt system.

So I guess the best thing for me to do is reduce my batteries to 2 instead of 6, giving me 225 aH, which is still too much, theoretically, but I don't want to but more PVsn and try to figure out where to place them.

So I ordered a Morningstar TS-45 per someone's recommendations, which I got today.
Here's my question (and I'm only asking it here because Morningstar is closed for the W/E, and I'm anxious to start charging then equalizing my batteries 2 at a time, in hopes of salvaging some):

MS says you have to have 2 of their units if you want to have both a charge controller and a load controller. This is the first I've heard of a load controller. So what does this mean? Page 6 of their manual has a diagram of how to hook up the TS-45 as either a charge or load controller. What disconcerts me is there is no indication of where to hook in the LOAD if you are using it as a charge controller. Does this mean I can only charge the batteries with this, and if I want to actually run anything on the batteries I need a 2nd TS-45, or did they just neglect to indicate where to hook up the load?

mike95490 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Loohan wrote: »

This is the first I've heard of a load controller.

The load controller is a relay/switch inside the Charge Controller box, that all your loads are connected to. When battery voltage drops low enough to become dangerous to the longevity of the batteries, it switches off All Loads, and preserves the batteries till they have recharged somewhat. Some inverters have a "low voltage disconnect" in their inputs, that does the same function, only for that single inverter.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

That makes sense, Mike, but let me quote the manual:
1.2: There are 3 distinct and independent modes programmed into each TriStar. Only one mode of operation can be selected for an individual TriStar. If a system requires a charging controller and a load controller, two TriStars must be used. (It then lists 3 modes: charging, load control, diversion.)
2.2: diagram shows "load" OR "solar array" as alternate things to hook up to the same wires.

niel · July 2007

Re: REDUCING AMPERAGE for delicate electronics

sounds like diversion controller being a load controller and not a low voltage disconnect. that someone i remember was crewzer on the 1w of pv = 1ah of battery capacity. i don't know of the validity of this statement and it can't be true in all cases, but i seem to recall crewzer mentioning it for 12v systems or something like that. the ah for say 200w of pv will be different(1/2 as much) when the batteries used are 24v rather than 12v.

SolarJohn · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Loohan,

Upon reading this thread I'm not sure that your question about whether or not you need two charge controllers has been answered. I have a moningstar 20a charge controller that I use in the Charge Controller mode. My inverter is connected directly to the batteries, not through the charge controller. I think that is the right way, and I think that is what you want to do. I see no need to connect a second charge controller (in load control mode). My inverter shuts down if it detects low battery voltage, so I don't need that functionality in a second charge controller.

By the way, I'm thinking of getting a Morningstar TriStar 60. I hope to be able to monitor my system remotely, using software available for it. It's not really clear to me at this point how I will get the charge controller tied into an Internet site.

My PV array is too small to take advantage of the benefits of a MPPT charge controller, and I don't want to spend the extra $$ that one of those costs anyway. I like the DC to DC conversion capabilities of the Outback MX-60, but again, it comes at a price. (Sorry, just thinking out loud).

John

crewzer · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Loohan,

Someone (another missing post?) said that I should have a max of 1 aH of battery for each watt of PV, and that I have 675(?) aH on my 160-watt system.

That was me. I probably said something like “a useful rule of thumb is to have 1 W STC of PV array power for every 1 Ah of 12 V battery bank capacity”.

MS says you have to have 2 of their units if you want to have both a charge controller and a load controller. This is the first I've heard of a load controller. So what does this mean? Page 6 of their manual has a diagram of how to hook up the TS-45 as either a charge or load controller. What disconcerts me is there is no indication of where to hook in the LOAD if you are using it as a charge controller. Does this mean I can only charge the batteries with this, and if I want to actually run anything on the batteries I need a 2nd TS-45, or did they just neglect to indicate where to hook up the load?

When using a single TriStar as a charge controller, your loads (i.e., an inverter) should be connected directly to the battery terminals via a breaker or fuse. This is a fairly standard configuration and not unique to the TriStar. Some Morningstar controllers (i.e., the ProStar) include load connections and integrated load control features (such as low voltage disconnect), but the TriStar does not.

HTH,
Jim / crewzer

crewzer · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Solar John,

By the way, I'm thinking of getting a Morningstar TriStar 60. I hope to be able to monitor my system remotely, using software available for it. It's not really clear to me at this point how I will get the charge controller tied into an Internet site.

Is the information available from these links helpful?

http://www.morningstarcorp.com/products/TriStar/info/TS_WebView_DataSheet.pdf
http://www.morningstarcorp.com/products/TriStar/info/TS_Guide.pdf

HTH,
Jim / crewzer

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Thanks, John and Crewzer.
Yes, I had kind of figured that I should just connect the load to the battery. After I made that post, I noticed on Morningstar's little promo brochure a stylized diagram of a TS with a panel connected to it, as well as a battery, and an inverter connected to the battery.
But I don't ordinarily use an inverter, and have no low-voltage disconnect. Is there an easy way around this? Do they make disconnects as a separate module I can connect to the battery?

BTW, my MPPT 200 cost about $70 3 years ago, but the float voltage adjustment drifts too much for my liking.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Loohan wrote: »

But I don't ordinarily use an inverter, and have no low-voltage disconnect. Is there an easy way around this? Do they make disconnects as a separate module I can connect to the battery?

Actually, I do have a buck-booster http://www.powerstream.com/dcdc.htm on its way. It says it has the following protections:
(1) Input polarity protection. \
(2) Input low voltage drop out [power off reset]
(3) Input high voltage protection [power off reset]
(4) Output short circuit protection [auto reset
(5) Output current limit [auto resume]
(6) Over temperature protection [power off reset]

although it is not clear whether the low voltage part is adjustable. Also it says "High efficiency 75-85%" so I may not want to run everything on it.

crewzer · July 2007

Re: REDUCING AMPERAGE for delicate electronics

"…have no low-voltage disconnect. Is there an easy way around this? Do they make disconnects as a separate module I can connect to the battery?"

Loohan,

Here are several off-the-shelf solutions to consider:

1) http://store.solar-electric.com/ss-10l.html (only use the battery and load connections)
2) http://store.solar-electric.com/volconswit.html
3) http://store.solar-electric.com/moredr.html

HTH,
Jim / crewzer

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Thanks, Crewzer! But dang, isn't there something more cost-effective?

I pretty much decided not to put all my stuff on the buck-booster, due to efficiency losses, but I suppose I could at least temporarily.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Then again, that last one looks like it provides a lot of useful info. I may get it down the road a bit.

crewzer · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Yeah, that relay driver looks like it may well be pretty fexible and useful, especialy when used with the TriStar controller. You can download its programming and control software for free and check it out on your PC. See: http://www.morningstarcorp.com/products/software/index.shtml

Good Luck!
Jim / crewzer

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

Yeah, and even further down the road I might buy a PC. The one I got is on its last legs. I use a Mac.

System2 · July 2007

Re: REDUCING AMPERAGE for delicate electronics

DOH! I just had a cosmic flash of insight, getting back to the original topic of this thread.
I already have the buck-booster which converts everything to 12V. Haven't used it yet.
With this logic relay device, I could make the buck-booster cut in at say 13.4V (battery output) and cut out if it went below 13.1V for more than 5 minutes or whatever. That way, I could get rid of the high spikes without losing so much efficiency.

REDUCING AMPERAGE for delicate electronics

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