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Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread
« Last post by neo on Today at 05:11:37 AM »
With my new scope (Tektronix 7704A) does it require probes built special for it or will common probes work?
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Yep, still runs on god juice.
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Beginners / Simple op amp circuit need solving
« Last post by ZeTeX on Today at 05:10:23 AM »
I need to find the equation for Vo2.
The answer is Vo2: -4*V1+2.666*V2
For Vo1 its easy it is just -3*V1, but for Vo2 there are 2 resistors going to the non inverting input and it is confusing, I'm not exactly sure how to solve such thing.


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Beginners / Re: Li ion battery pack charging & BMS
« Last post by Adhith on Today at 05:07:41 AM »
1 cell with 5800mAh? Those are big ones. For a cell with 5800mAh, 1C means that you charge at 5800mA which means 5.8 Amps. 2C would be twice as much so 11.6Amps, or 0.5C means 2.9Amps . These numbers are for cells connected in serial. If they are parallel you can multiply that by the number of cells.

Another example, having 4S2P, so 4 in serial, and these 4 another time in parallel. So 2 blocks, where each block consists of 4 cells in serial. These two blocks are connected parallel. Resulting in 8 cells total would result in Capacity * number of cells, which is 5800mA * 2 => 11.600mA => 11.600 Amperes

Please check the datasheet of your cells regarding the C rating, that's usually specified there. 1C may be a good rule of thumb but I saw cells which take more or even less.

Charging the cells with too much current can result in a steam/fire/explosion.

I sometimes use twice the specified current, but I also check the temperature every 5-10 minutes since it's really dangerous. I think fast charging also reduces the livetime so better stick to the recommended values.

Edit: Also very important: If you connect cells parallel  you need to ensure they are evenly charged. If one cell is full and the other one is empty, the full one will charge the empty one uncontrolled. It might be possible that the current is way too high and the empty cell starts steam/fire/explosion.

And as katzohki said, use balance charging. That means if you have cells connected in serial you have an additional wire between each cell.

So for a Block of 3 cells it looks like this: -C x1 C x2 C x3 +

C is a cell, - is minus, + is plus, x are balancing connectors. Where minus and plus give you the total voltage of the block. x1 is the first balancing connector providing 4.2 volts between - and x1, x2 is the second balancing connector at 8.4 colts between - and x2, and x3 is the same as + giving you the total of 12.6 Volts. A balancing charger can use these different voltages to determine the voltage of each cell, and these points are also used to charge cells independently. The balance charger first charges the empty batteries until all batteries have equal charge, then they are charged together.

In whatever way cells are connected, serial or parallel it's getting dangerous if they are not charged equally.

Edit2 You should also think about buying a battery charger from the car/airplane/quadrocopter area like the Imax B6. I'm really happy with mine, I can charge EVERYTHING with it. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR12.TRC2.A0.H0.Ximax+b6.TRS0&_nkw=imax+b6&_sacat=0
But for your case you might want to look for a stronger one which can provide more Amps.
Thankyou very much adras for the detailed explanation for my questions, but i still got somethings to be cleared before going further.
1)So for a 5800mah battery 1C means 5.8amps, i got it and I'm planning to go for 1/3 C as the charging current. but I have seen on internet that the real capacity of batteries are quiet less than specified so do I really want to take into account the specified value of 5800 or better take around 3000 or less to be practical??
2)Regarding the 4S2P battery pack would it be good to make 4 groups of 2 cells in parallel first and then connecting the 4 groups in series?? thus making it easy for balancing (I'm using a BMS with balance option).
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Metrology / Re: Calibratory D-105 DC Precision Voltage Reference Standard
« Last post by Gyro on Today at 05:07:12 AM »
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Among our customers are two US Military defense contractors

That's just shocking!  :o
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General Chat / Re: Bringing a DIY battery powered device in flight?
« Last post by David Hess on Today at 05:06:54 AM »
One issue though, the first xray exposure seems to have damaged the eeprom as a few of the values stored in memory gets wiped out at power down, it worked before as i have been using it on the road so code is not at fault.

It would take a huge amount of x-ray exposure to damage an EEPROM beyond just erasing it.  X-rays can actually be used to erase them just like ultraviolet except you can apply x-rays through a package.  Even erasing floating gate memory takes a much larger dose than will be found in an x-ray scanner.

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Interesting fact: i was seated beside the window on the rearmost seat of the plane. I was able to get up to 8 satellites locked but then everything disappeared at cruising speed and altitude. It came back when the plane slowed down nearing the destination. I suspect it is static electricity from the wind and exhaust swamping the gps signal. Let's see how it fares on the connecting flight. Waiting to board right now. :)

That should not happen.  What GPS was this?  I think it more likely that the software has built in limitations beyond those required for civilian GPS receivers.
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... I just popped the cover off of the 5327B and discovered that it has a TCXO in it.  It's on a vectorboard edge card, but may well be custom from HP - the unit has a non-standard serial number (SC-94), so my guess is that it's built to some customer's specification.  The date codes on the parts are in the same ballpark at least.



That's an interesting frequency setting. "Yeah, can you make us a special 10 MHz TCXO? Set it 1.0 Hz high, please."  ;D
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You must be young. As you get older you realise your life is finite, and you have to choose how to spend what's left.

Myself, I enjoy helping other people learn more and do more than they believed they could. I try to pick people where that will happen.

I deeply resent people that piss around and play silly thoughtless games, because it stops me helping someone that could benefit from my time. Others feel the same.

To put it another way, how would you feel if you had gone to the trouble of trying to help someone, only for them to turn round and say "oh, ha ha, my game, I didn't need your help anyway".

I agree, 'rhetorical questions' are a PITA; I'm much too old for playing games.  The simple solution is to just ignore the posts and move on.

It's sometimes difficult to separate the folks with a legitimate question from those who are just trolling.

Just so.

However this one shows signs of listening and understanding (kudos to them!), so there's the possibility of redemption followed by a useful life  ;)
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We welcome anyone to come to our facility and view our traceability documents and calibration procedures. Our products live up to all of our claims! And we have two separate calibration labs.

That is a nice offer but being thousands of miles away I'm not able to come, maybe you could just post some pics here?
Or a video tour on youtube?
That would be best and could potentially boost your sales.
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Buy/Sell/Wanted / Re: TOPLOSER - buying Review from Fraser
« Last post by onesixright on Today at 05:04:03 AM »
I second that.

Great guy, more then reasonable prices. No bs with shipping costs, etc.!

Not something to take for granted these days.

Big thumbs up.  :-+
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