3 in 1 Question - Don't want to overload the board with too many posts

[valterra]

QUESTION 1:

I have one of those emergency car jump starter dealies.  Pretty similar to the one on this page.  Mine also has 5V female USB plugs on it.

It has 2 big clips (think Jumper Cables).  It charges its internal battery by plugging into the cigarette lighter or using an AC Adapter "wall wart."  There is a small female jack to use with the cigarette or wall wart.

I have my wind generator's wires running into my home-made battery pack.  From what I understand, this car starter thing has something like a 7A SLA battery inside.  So I wanted to incorporate it into my system (too poor to buy another battery right now).

In order to hook it up in parallel with my other batts, I used those big clips.  But I got to thinking that maybe there's some kind of diode in there that prevents voltage from running back into its internal battery pack.  I don't want to take it apart, and so I don't know how I'd test that.  So in addition to using the big clips, I also ran a wire from my other battery pack and plugged it into the front.  The "Charging" LED comes on, so it must like what I'm doing.

There's nothing wrong with that, is there?  There's no short.  Everything is hooked up in Parallel.  But it just seems kinda weird that it is sending electricity back to my other batteries through the clips, and getting it back from those same batteries through that little barrel connector in the front.  

QUESTION 2:

I have a 20A regulated Power Supply.  Here's a link to one.  It's 13.8VDC and what I used for my Ham Radio gear.

I'm thinking that the easiest way to incorporate my new (and soon-to-be-finished) renewable energy stuff into my current house setup would be run stuff from the 12VDC battery bank as long as possible, until the batteries drop too far in voltage.  At that point, I want the mains power to "kick in" and keep supplying the voltage while the batteries recharge.  

This power supply could certainly perform the latter part, using DamonHD's circuit idea.  But is that really necessary?  Can this power supply be incorporated into the circuit somehow, without having to be switched in and out all the time?

QUESTION 3:

How to I measure how much current is going into my batteries?  My DVM's instructions say that current is measured in Series with the load.  But that would mean unhooking my genny from the bank, allowing it to spin freely until I plug the meter and the batteries back in.

My system is an Ametek motor, 12V battery pack, and my voltmeter says it can measure up to 10 Amps.

Here's a simple diagram to make it easy.  Where do I tap to measure current?  

(The little arrow with the lines is my diode.)  I've measured "a -> c" which I know is shorting the mill.  I'm thinking that I need to split "b" and insert the meter there.  Boy, them's some fancy graphics, ay??

Also, does the voltmeter act as a (significant) load?  Because I get all kinds of weird readings as if my mill is winding down when I plug it in.  If so, I'm wondering how one would insert an ammeter into the circuit anywhere.

Thanks!  And hopefully it's not obnoxious that I put all 3 questions in one thread.  I didn't want to post 3 separate messages within 10 minutes.

[SparWeb]

Asking 3 questions in one posting is okay by me - you don't want to be called a "forum-hog"!

I'm only going to address question #3.  A voltmeter shouldn't put any load on the system it tests at all, otherwise it wouldn't be a useful tool.  The impedance (resistance) is several thousands of ohms, so don't worry.  No current goes through that circuit.  Funny Voltage readings can come from the messy wave form a generator creates.  There's probably a few blips that upset the otherwise steady DC reading from your Ametek, as the brushes change poles on the commutator.

An Ammeter, across "a" and "c" is a dead short, and that will definitely affect the windmill!

It sounds like what you actually have is a digital "multimeter".  I'm being picky about the terminology just to make the point clearer, not because I think you don't know the difference.

An ammeter must be in series to measure current.  A voltmeter must be in parallel to measure voltage.  AND you CAN'T do both at the same time with the same meter, so don't try.

Using a multimeter to measure current, temporarily, is troublesome, for the exact reason you give:  you would unhook the windmill from its battery load and it would run free for a moment.  The connect/disconnect process also involves lots of sparks, a clear indication that you shouldn't do it.  And then you are also likely to blow the fuse in the multimeter, once again releasing the windmill to spin freely.

You should put in a dedicated ammeter, in series with either the + or - side (doesn't matter which, if your system is really simple).  For the time you spend putting it in, short out the leads from the windmill to prevent it from running.

Steven Fahey

[terry5732]

#1

The instructions say don't use it when charging. The charging circuit in these is ridiculously fragile. On all of the ones I've opened the only thing between the battery and the cables coming out is a switch - no diode. You can charge through the cables like any lead battery as long as the switch is in position to allow it. I can't imagine what it would have a USB plug for?

[jonas302]

I can help with question #1  on all the booster pack I have taken apart the cables were direct to batt and the charge board hooked up paralell also so should be fine mine usually have 17 amp hour batterys usually solar brand

a lot of times with the cheap one the charge board went out so we stil made use of them by charging though the battery clamps

[wdyasq]

For Measuring current I suggest a 'shunt'- You will need to look up the details and design a proper 'shunt' for your system.  With the 'shunt' in place one can measure voltage and/or amperage.

[frackers]

1. My answer to this would be a trip round the local garages and junk yards and pick up a couple of old truck batteries - you'll easily pick up one of 10 times the capacity and with careful charging even the roughest quite often recover OK. Take your multimeter with you and check that any battery you scrounge up shows at least 10.5 volts.
   
2. 10,000 possible solutions to this so I won't even go there!!
   
3. Back to the junk yard and get a car/motorcycle ammeter. They show either 30-0-30 or 50-0-50 amps and go in line with the connection to your battery bank so you can read what goes in and/or out (i.e. not in the genny line as that only shows what is going in).
   

[valterra]

But where on earth do you find a real, analog ammeter?  Harbor Freight has one here, but it seems like it'd only give a rough estimate.

Oreilly Auto Parts seems to sell some for your dashboard.  They're significantly more expensive than harbor freight's one.

[valterra]

Thank you for that - the only places I'm finding ammeters is auto parts stores (and harbor freight has one for $2.99).

[valterra]

You're right - it's a digital multimeter.  It's the one everyone talks about that goes on sale for $3.99 all the time at Harbor Freight.  It has a 10 Amp setting.

I placed it between the diode and the Positive side of my battery bank, and it didn't show anything.  Then every once in awhile a number would show up.  Usually in the range of 0.01 to 0.80 Amps.  The number would rise and then fall.  Finally I realized - duh - it won't show ANY current unless the genny reaches cut-in speed.  And with these bursts of evening wind, it makes sense that the level would rise and then fall.

And with those numbers I can sort-of "watch" my blades spin up and slow down.  That's much better than watching the voltage jump all over the place.

Thanks for your help guys!  I want to measure both current AND voltage.  I've read into shunts, and the idea makes sense.  But I think for me, a dedicated Ammeter is the way to go.  I suppose a car's battery meter could do the same thing for me too.  That way I could watch the meters move around.  For some reason, I think moving needles look more authentic than changing digital numbers... well, then the geek half of my brain loves watching the numbers constantly change on the DMM.   :-)  :-)

[valterra]

Thank You!  I was wondering that exact thing.

[jonas302]

Dan made a really cool one there was a update story on it about a month ago http://www.otherpower.com/otherpower_experiments_ammeter.html

I have one out of a battery charger 0-50 in 10 amp markings inductive type so you just pass your wire though the back no connections send me your address if you want it I would gladly send it to a good home jonas302  at    yahoo  

shunts are nice to make a real accurate meter if you have an old voltmeter from   a radio or such relativly easy to make once you understand how they work

[finnsawyer]

For those who have analogue meters they may have noted that the things as voltmeters are rated so many ohms per volt, say 20,000 ohms per volt on dc.  What this means is that you multiply the full scale voltage reading by the 20,000.  On the 10 volt dc range the meter has an effective resistance of 200,000 ohms.  On the 50 volt range the resistance is 1 million ohms.  On ac the rating is usually less.  

[ghurd]

I only opened mine to see what fell out of the compressor.  :-(

But when I was using it to jump-start 2 or 3 times a day, After the car started, I left the big clamps connected for 45~60(?) seconds to recharge.  Did it like that for a couple months, and the internal 17AH battery always showed full.

USB for iPods, cell phones, cameras, flashlights, PSP, GPS, AA chargers...

Some newer inverters have a USB output.

China will no longer approve a cell phone for use in China unless the charge input is USB.  I expect they will keep selling us ours where no 2 are the same.

G-