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#11
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2-Batteries
Thanks Gary for the writeup. I have been thinking of doing the exact
same for a glider I just bought. Can you please add the part number if you recall them. I suppose if one really wants to know about the condition of each individual battery, you could put a voltmeter on a 3-way switch and see the volatge on the "main" bus, and each of the batteries. This way you could tell the difference between them. Gary Emerson wrote: Nyal Williams wrote: I'd like to see a full write-up with diagrams, photos, and names/addresses of places to buy parts. This would make a good article for Soaring. Here is a sketch http://www.mydatabus.com/public/emer...y/e/sketch.JPG and a pic of my install... http://www.mydatabus.com/public/emer...y/e/diodes.jpg There is a aluminum bracket which is lightly mounted to the bulkhead. The PC board just provides insulation and some support for the wires. Each diode has a heat sink, but I don't really think it was necessary. I don't have the part numbers handy, but I'll see if I can't find something. With 18Amps of forward current capability (each), there isn't really any "need" for the two diodes in parallel, but for an extra $5 and a few extra minutes of wiring, if any one diode ever did fail "open" the other would still provide power. Most likely overkill. |
#12
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2-Batteries
Eric Greenwell wrote:
wrote: By all means a second battery should be installed in our electrically driven modern sailplanes. After many years of quickly flipping my 3-position battery switch, and trying not to have my logger to momentarily dropout, I thought all loggers just started again after a momentary power loss, and continued the same flight file. It sounds like yours isn't behaving properly, or are some brands a bit touchy? There are some earlier approved flight recorder designs that will start a new flight data file if the 12V power supply is interrupted momentarily. The specifications were then changed to eliminate this behavior from newer designs... Marc |
#13
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2-Batteries
A quick Google of Schottky Diode and TO-220 yielded some sources.
I just tried the first one and then found this: http://www.onsemi.com/PowerSolutions...do?id=MBR2515L looks like even slightly better than what I had bought. You'd lose about 0.3 volts during normal operation. Datasheet at: http://www.onsemi.com/pub/Collateral/MBR2515L-D.PDF I'm sure some googling will find that someplace like DigiKey will have these and will take small ordering quantities. Is Paul Remde out there? Might be a nice "kit" to add to your line. Kit includes 4 diodes, 4 heat sinks, 4 insulating washers some heat shrink tubing, etc.?? Good luck. Gary Emerson wrote: Nyal Williams wrote: I'd like to see a full write-up with diagrams, photos, and names/addresses of places to buy parts. This would make a good article for Soaring. Here is a sketch http://www.mydatabus.com/public/emer...y/e/sketch.JPG and a pic of my install... http://www.mydatabus.com/public/emer...y/e/diodes.jpg There is a aluminum bracket which is lightly mounted to the bulkhead. The PC board just provides insulation and some support for the wires. Each diode has a heat sink, but I don't really think it was necessary. I don't have the part numbers handy, but I'll see if I can't find something. With 18Amps of forward current capability (each), there isn't really any "need" for the two diodes in parallel, but for an extra $5 and a few extra minutes of wiring, if any one diode ever did fail "open" the other would still provide power. Most likely overkill. |
#15
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2-Batteries
Testing AH of batteries
Battery capacity is measured using a defined minimum voltage. That voltage may or may not correspond to the minimum voltage your glider equipment will operate on. If you use diodes, that minimum voltage will move slightly. Capacity also depends upon a starting voltage - which is significantly higher than 12 volts. I often need to test batterys used in our search and rescue radios and have found that I can test battery capacity quickly without a full discharge. I charge the batteries, then let them sit for a day. Then, I put a load on them and simply watch the decay of voltage over time. In a very short time, you can make a graph that will indicate the trend of the battery and compare with a new battery. A battery with reduced capacity will drop voltage much more quickly. You can determine the capacity of the battery during charge, too. Capacity is the ability of the battery to resist change. That applies either way. it means the battery will drop in voltage or charge more slowly. So, you can simply time the charge of two batteries and learn the comparative capacity of each. Colin |
#16
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2-Batteries
Gary Emerson wrote:
With 18Amps of forward current capability (each), there isn't really any "need" for the two diodes in parallel, but for an extra $5 and a few extra minutes of wiring, if any one diode ever did fail "open" the other would still provide power. Most likely overkill. Yes because most often (probably at least 90% of the time) a diode fails "short" Therefore you may be reducing the reliability. :-) ...lew... |
#17
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Deturbulators was 2-Batteries
John Galloway wrote: Noone picking up on Dick Johnson's last paragraph?? http://sinhatech.com/SinhaFCSD-Progress-12132006.asp John Galloway The results are interesting, but way do the testing on a Std. Cirrus? To be taken seriously put them on a modern ship and test them. I can't believe Dick did the testing on the Std. Cirrus and did not at least put them on his Ventus for some additional comparisons. |
#18
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Deturbulators was 2-Batteries
If the numbers are real, that Standard Cirrus is now a 41-1+
sailplane-and that IS a serious improvement. $16K for a 41-1sailplane is great, and a boon for a lot of people that do not have $40K-60K for that type of sailplane performance. Looks like some older sailplanes could be hanging out with a new crowd. Mike wrote: John Galloway wrote: Noone picking up on Dick Johnson's last paragraph?? http://sinhatech.com/SinhaFCSD-Progress-12132006.asp John Galloway The results are interesting, but way do the testing on a Std. Cirrus? To be taken seriously put them on a modern ship and test them. I can't believe Dick did the testing on the Std. Cirrus and did not at least put them on his Ventus for some additional comparisons. |
#19
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2-Batteries
With the diode solution, when the system is turned on the battery with
the highest voltage will provide the current. As the battery draws down the second battery will come on line. From that time on both batteries will be providing power to the circuits. The strongest battery will provide the most current but both batteries will be stabilized at a common voltage. Therefore BOTH batteries will require re-charging after being used for any substantial period of time. Regarding the 3 position switch. The simple solution is to put a capacitor between ground and the output side of the switch. The capacitor must be large enought to provide the current needed during the switch switching time. This should not be a very large capacitor for our purposes. Brian Utley Gary Emerson wrote: COLIN LAMB wrote: "If both batteries are on-line all the time, how do you know when one is getting weak and needs to be replaced? Or do you replace both batteries when voltage is marginal at the end of a flight?" Well, that is a problem. You do not know. Everything is automatic. If you have one battery that has lost most of it's capacity, the good battery will do all the work. The only way you will know is when the total capacity of both batteries has been reduced. And, then, you will not know whether one battery has done 50% of the work and they are both down in storage ability, or one battery is still 90% and the other one is 10%. So, you will have to determine the capacity of each battery separately. You could test the battery capacity by switching either off during discharge, or even by using 2 ammeters - but it is becoming more complex once we try to extract more information. You can also determine the capacity during charge. Colin During any one flight, you don't need to know. What is a good idea is to test the batteries if you think you are losing capacity. During the week charge them up Monday and Tuesday, and Wednesday put a load on each one and see how long it lasts. Ideally, you'd like the load to test the batteries for as long as you'd normally fly. Say 4-6 hours unless you are typically flying for longer. If either one can't go the 4-6 hour distance and mainain a suitable voltage, then it's due for replacement. After the Wednesday test, charge them back up so you're ready for the weekend assuming they pass. I'd certainly do this in the spring and before any big contest during the year. 7Ah batteries are cheap in the grand scheme of things. |
#20
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2-Batteries
This is great discussion. I was doing a bit of research myself (it has
been over 10 years since I did any HW design, so am pretty rusty). Another option that sounds even better is to use the new chips designed for exactly this to control DirectFETs. That way the voltage drop and power waste will be significantly reduced with very little additional cost. The chips I were looking at were IR5001S: http://www.irf.com/product-info/data...ta/ir5001s.pdf or LT4351: http://www.linear.com/pc/productDeta...,C1079,P21 73 I have used DirectFET stuff in robotics and found them to be very reliable and very simple to design with. My biggest problem is all these components are only available in surface mount these days and I have never tried to build a circuit using them. |
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