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Voltage Reading Conflicts

Old 11-28-2008, 07:01 PM
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Default Voltage Reading Conflicts

Guys,

I own a Brian 977 Charger. I also recently purchased an Astro Flight 101 Super Watt Meter.

When checking my voltage, there is a fair sized discrepancy between the two meters. On a 3 cell lipo, the Astro consistently reads between .3 and .4 higher volts higher than the Brain. For instance, the Brain reads 11.80v and the Astro reads 12.20v. I don't want to overcharge my batteries and the Brain will kick off at around 12.35 volts but the Astro will read 12.60 volts on the same battery. Not good from what I understand.

Any suggestions? the only thing I can think of is buying another meter to verify one of the two units, but I really don't want to spend more money. Any input is appreciated.

Thanks.

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Old 11-28-2008, 07:14 PM
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Heli Jim
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A reading of 12.6 is OK for a 3 cell LiPo
A fully charged cell is 4.2 volts. 3 X 4.2 = 12.6
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Old 11-29-2008, 01:21 AM
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Al_M
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You should never measure the same thing with more than one instrument. You will never get them to agree. If they agree, both will likely be wrong to some degree. Neither instrument is of lab guality. Most of us couldn't afford them if they were, but they are good enough.
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Old 11-29-2008, 03:00 AM
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kyleservicetech
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I've got one of the Astroflight Whattmeters, and have checked it against my Fluke 87V meter with a DC voltage accuracy of 0.05%. (Yeah, it's danged expensive!)

Results of testing one sample of the Whattmeter, mine is accurate to about plus/minus one percent on voltage, and within a few percent on the other readings such as watts, MaHrs and so on. Considering my Fluke meter costs 10 times more than the Whattmeter, that Whattmeter is impressive.
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Old 11-29-2008, 03:57 AM
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Guys,

Thanks for the input. I guess I was expecting too much. Al, your right neither is qualified as a calibrated piece of lab equipment.

Maybe I am over thinking this one , just trying to maximize battery performance without over charging.

Have a great weekend and good flying if you get out there.

Thanks

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Old 11-29-2008, 07:40 PM
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I have one of the $5.00 battery monitors (pic below) and a G.T Power A6 charger, both from HC, and they read within .02 volts of each other. I also checked it with a good quality (not lab quality, though) and got the same readings. All three devices seem to pretty well agree with each other.

Bill
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Old 11-29-2008, 07:44 PM
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Bub Steve
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Originally Posted by Sir Raleigh View Post
I have one of the $5.00 battery monitors (pic below) and a G.T Power A6 charger, both from HC, and they read within .02 volts of each other. I also checked it with a good quality (not lab quality, though) and got the same readings. All three devices seem to pretty well agree with each other.

Bill
Sir Raleigh'inBUB::I like mine as well, get's closer that ball-park but not dead on, bub, steve
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Old 11-29-2008, 07:54 PM
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Hi Steve.

I use mine more as a 'fuel gauge' than anything else. I have it attached to the battery on the plane and each time I land I look at it to see if I can get another flight out of it. I'll change out batteries when the total voltage is between 11.1 and 11.3 volts. Never reached LVC on the plane yet.
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Old 11-29-2008, 08:06 PM
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Bub Steve
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Originally Posted by Sir Raleigh View Post
Hi Steve.

I use mine more as a 'fuel gauge' than anything else. I have it attached to the battery on the plane and each time I land I look at it to see if I can get another flight out of it. I'll change out batteries when the total voltage is between 11.1 and 11.3 volts. Never reached LVC on the plane yet.
Bill: Didoe my bub, steve
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Old 11-29-2008, 09:48 PM
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Originally Posted by Sir Raleigh View Post
I have one of the $5.00 battery monitors (pic below) and a G.T Power A6 charger, both from HC, and they read within .02 volts of each other. I also checked it with a good quality (not lab quality, though) and got the same readings. All three devices seem to pretty well agree with each other.

Bill
Sir Raleigh,

Only off by .02v sounds pretty good, my two meters are off between .3 and .4 depending on the voltage of the battery. I thought they should be closer.

Thanks

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Old 11-29-2008, 10:03 PM
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Sir Raleigh
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I think they should be, too.

Do you have the manual that came with the meter?
If so, does it show in the specifications the accuracy of DC Voltage around 10-20 Volts?

The one I got from HarborFreight shows:
2000mV - 200V = 1.0% 1 Digit

That would be about 0.12 Volts error when measuring 12 Volts.

Not too bad for a $3.00 Multimeter
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Old 11-30-2008, 01:07 AM
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Hello folks
A a novice as regards electric flight and as it seems to me at least there is a lot of information about on how to get started etc, particularly on this site which is excellent. As a raw beginner I would be grateful if any fellow member could point me in the right direction regarding Li-Po batteries, charging them, a suitable charger preferably simple to use and last but not least relatively cheap, which tells me the state of charge in the batteries and balances the batteries, and tells me by sound or whatever when they are charged, as I understand it can damage the battery if it is overcharged or indeed allowed to drop below a certain voltage, and indeed can be dangerous according to what I have read in various articles to be honest I am rather confused!!. When it comes to understanding all things electrical!!
Also how do you discharge the batteries if this is neccesary?, I have read tonight on the site an article about something called a "wattmeter" costing $5.00 and a G.T. Power A6 charger are these the type of things I am looking for? if so are they available in the U.K. I have two Li-Pol batteries rated at 1250 mAH,11.1 v, and 10c discharge? and also a balancer charger for 2&3 cellls, which came with a Park Flite RTF Super Cub which I bought recently, I used to fly radio control i.c. models quite a few years ago and I only used Nicad battery packs which to me at least were easy to charge etc, however I understand that given the advances in battery tecnology electric motors etc Li-Po batteries are the way to go in electric flight which I really want to move on to. Any advice would be much appreciated.
Thanks in advance,murphy.
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