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CamLight Systems PD-12V Two-Stage Battery Discharger
By jabbie
Mar 29, 2005, 01:00 AM
Introduction
I have been a very enthusiastic and active electric model pilot for some time now. I can charge many flight packs using four chargers, powered by two 12 Volt DC power supplies, and be ready to fly at an hour or two's notice. But often I'm off to the field, only to find it's started raining or blowing even harder than I wish to fly in, without any weather warning, as, or even before I indeed reached the flying field! Ugh! So what? It will be OK tomorrow, right? The tomorrows come and sure enough the weather is much better, so I top off the flight packs that I charged on the previous day and off I go. We all do....right? Time went by and one day I hand launched a plane only to see it landing a few yards in front of me, in fact I was lucky it came down level. What was wrong? The pack had been charged as normal. I tried a second pack and that was not much better. For those of you with lots of experience, the penny may have already dropped. I tried to recover the packs with the recommended countless cycles, carried out on different good quality chargers, with little or no improvement. What shall I do? I scratched my head and turned to my PC. Let’s get on the net! I did a search for cycling, charging, discharging, batteries and flight packs...and, low and behold, found a company in New York that specialized in the very thing I was seeking, a stand-alone discharger. So I sent John Muchow at CamLight an e-mail and we started chatting. I told him of my problem and he said he could help. After many very constructive and long e-mails from both sides, he decided to send me the prototype of a new unit his company was developing, for my trial and appraisal. Six days later the discharger arrived in the post and the testing began.
The DischargerThere are 2 units in this excellent set-up, one is the PD-12V Pack Discharger and the other is the LM-12V Load Module. I nicknamed the second “the loader”. They each stand-alone, which means there is no need for a power source of any type. The pack that needs discharging simply plugs into the PD-12V and is discharged in 2 stages. The first is a rapid discharge around 10A (for 10-cells) and the second much slower, around 1A. The purpose of this is to let the pack cool as the last drops are withdrawn, ensuring a complete discharge. Each cell is taken down to 0.9V. So far all tests have shown that no harm has come to the packs, in fact old packs have been revitalized. Fitting the loader adds 100% to the discharge rate, so the pack then discharges in half the time.
The handbook for the prototype stated:
MY TRIALS WITH THE FIRST PROTOTYPE UNITS:
First I took a very tired and I believed useless NiMH 3000mAH pack, one that I thought was destined for the recycle bin. I put it on the discharger...and the result, as expected, was... not a thing, flat as a pancake. I charged the pack and it peaked at only 650mAH. Back on to discharge! Then on to my Schulze 6-330d charger...and...bingo! 3000mAH. At that time I had no means of telling how much had been taken out by the discharger from the cells...I have since purchased an Astro watt meter, a very good product and one (or similar) that all electric flyers should have, which can now provide me this information. Then I tried another weak 3000mAh pack, well this one was a little better. On the first charge the pack reached 1800mAH, then to the discharger and back on the charger. Results at 2600mAh were not as dramatic as before, but still significant improvement. Maybe it will get to full capacity next time around. OK lets try a better pack still, this one is an 8-cell 3000mAH NiMH pack that normally gets to around 2400mAH. It's done a lot of work, but is still OK. Charged as normal 2400mAH, on to discharge, then back on charge, 2600mAH. Only a small increase, but still nearly 10% further improvement! After 3 more cycles this pack came right up to capacity at 3000mAh. Having made some suggestions to John Muchow (the inventor), I sadly and only after his adamant request, sent the units back to New York. The good news was, I was now awaiting what he promised as a much-improved production discharger. He indicated the new unit included a few upgrades based on suggestions of mine and many of his own!
TESTS WITH THE NEW UNITS USING AN ASTRO WATT METER:
The official names for the new units: the discharger is PD-12V and the loader is LM-RES-12V. The web site offers in total four Pack Dischargers, two Auto-Cutoff Modules, and two Load Modules, all power-resistor based. I first took a well-used and badly-stored transmitter pack of 6-cell RC2400, that was in a state of discharge, and would no longer power the TX, and put it on my charger. All it would take was 1100mAh. The pack was obviously taking far less charge than it should. Next onto the discharger and at 14.8amps it took out 1400mAh, more out than I'd put in. It then switched over to Stage-2 (this happens at 0.9v/cell), and it discharged a total of 1587mAH. Interesting also was that after the charge only 3 cells got warm (well quite hot), yet on discharge all cells got to the same equally warm temperature. It was time to recharge the pack. This time the charge got to 2100mAH, and not one cell was more than warm. The discharge showed 1810mAH at 14.8amps (all the cells this time had warmed to the same temperature) and the second stage removed a further 212mAH at 0.7amps. A total of 2022mAH had been removed from the flight pack. This proved that the pack needed further conditioning and that discharging (especially the 2 stage discharging) help the cells get back up to capacity. A further test showed a charge of 2100mAH...same results again (charge rate 4 amps) but the discharge this time achieved 1905mAH and that was before the voltage had dropped and Stage-2 started. Nearly 100mAh’s more of usable energy! The total discharge was 2097mAH. Not quite as strong I would like, but so much better than before using the discharger! OK lets have one more go. On the next charge the pack's capacity reached 2200mAH and discharged 1926mAH before the voltage dropped. How many more cycles before full capacity I wonder? After 3 more cycles the pack reached 2360maH. We're now at about 95%! I have 2 packs of 500ar’s. One always gets to over 600aMH, but the other only to 480mAH. So I put the lower rating pack on the discharger, with the loader attached. Immediately, Stage-2 cut in. I removed the loader and the pack, then started the discharge again without the loader. This time it continued as normal and then in cut the 2nd stage again. It seemed that the smaller packs didn’t handle the higher current being pulled from them. Proof that we shouldn’t draw high currents from small cells! However, taking the pack down to 0.9v per cell on stage 2, its capacity improved and it now performs like the other.
Even More New FeaturesSince I received my discharger, CamLight Systems has updated the products and added some great new features. The dischargers now have adjustable discharge-current levels (a choice of four current ranges) and adjustable per-cell cutoffs (0.8V-1.1V/cell).
Three new dischargers are now available:
Two Automatic Cut-off Modules, the ACM-15 and ACM-40F (15amp and 40amp maximum) are also available for those who want to use their own loads to discharge their packs.
CONCLUSION
The discharger is so small and light (about a 3.5” cube and weighing just 11 oz.), it can be taken with the Whattmeter to the flying site. There a pilot can check how much charge is left in his packs and for how much longer he could have stayed safely in the air. No more guess work! The 3000mAH NiMH packs that I first put on the early discharger are still reaching the makers claimed capacity; however, they do need the new upgraded CamLight discharge treatment each time I use them to maintain that capacity. One or two cycles do the trick. In the future they will most probably give up completely, but with so many more free flights from them, who cares? Packs, after all, cost lots of cash! Many of us already have meters to test our motor's current and no doubt many use car bulbs to discharge flight packs. How many use a meter in conjunction with discharging, so as to check the voltage the pack is taken down to? It is definitely worth some thought! We all agree that storing Ni-Cad cells in a discharged state is preventive medicine, helping prevent one or more cells in the pack’s voltage dropping below the others. (The jury is still out regarding Ni-MH; many say yes, some no.) If a cell is allowed to drop too much, it can consequently render the packs useless, well that was before CamLight came along. Now that dropped cell can be brought back 'into the fold'. It is still better when returning from the field with a few charged packs to discharge them and avoid this problem; however, at least now we can resurrect some damaged by our mistakes! We could've done this in the past with many of our regular charges. However, having to discharge at the low rates most chargers can give us is a very time consuming exercise. This discharger can do it so much faster and in my mind is worth its weight in GOLD!
A more technical look with Recurring Charge Columnist Bernard Cawley
I’ve been asked to give another look at the CamLight PD-12V discharger and LM-12V load module that John Beard wrote so enthusiastically about up above, so here goes.
Background
Battery dischargers are not a new idea, and at first glance this one looks like just another bunch of power resistors and some ancillary electronics. But it’s not quite that simple. Fundamental to CamLight’s approach, and different from anything else I’ve seen, is the idea that while fast discharges of batteries are probably good for showing what those batteries can do in actual use in our models, often they don’t tell the whole story. When discharging a pack, especially that’s been sitting for awhile or has a cell that is going bad at, say, 9A, it will reach the cutoff voltage with a considerable amount of stored energy still in the battery. Conversely, the slow charge/discharge cycling that devices such as the AccuCycle Elite , or even some high-end drive battery chargers, may be good for getting a good reading on total capacity at a low discharge rate, but they don’t do anything to give you an idea of usable capacity under real use loads. Also, slow discharges take a long time. CamLight’s approach is to combine both fast and slow discharging into a two-stage process, with the idea of getting the “real life view” benefits of a fast discharge along with the balancing and more complete discharge of a slow one, while shortening the time involved in the whole process compared to a normal battery cycler. There’s much more about what is going on here in the document “Why Discharge?” on CamLight’s web site. There's even more data here. As John mentioned above, the PD-12V is one of four two-stage dischargers in CamLight’s line. In production form, it is intended to discharge 4-10 cell nickel-based batteries at maximum voltage-dependent rates of 4-9.8A on the fast “stage 1” charge. Once the selected cutoff voltage is reached, CamLight’s dischargers then discharge the battery a second time, this time at about 1A until the battery’s voltage again falls to the selected cutoff. This approach gets a discharge cycle done quickly and yet, thanks to the second stage, does a complete job as well. As John also mentioned, there is also the separate LM-12V Load Module which, when plugged in to the socket provided for it on PD-12V, adds another fixed load that is active during the first stage discharge, effectively up to more than doubling the first stage currents.
Physical Aspects
The PD-12V is approximately a 3 ½ inch cube. The circuit board is protected underneath by a clear plastic shield (which also carries the label). Rising from the board are the power components, and a set of standoffs that support the cooling fan on top. On one edge of the board are two banks of DIP switches for setting the cutoff voltage during a discharge. Also on this side are two LEDs which indicate what stage of discharge the unit is in (or reverse polarity of the battery), and the start button. On the opposite side of the board is a smaller bank of switches which selects the load for the fast-discharge stage. Emerging from a third side is a heavy-duty power lead, to which the battery to be discharged is connected, and opposite that side is the connector for the auxiliary Load Module, used to increase the discharge current during stage 1 up to a little over double what the basic unit can do.
The per-cell discharge voltage is set to 0.8. 0.9, 1.0 or 1.1 volts by closing the appropriate DIP switch. This level is used for both fast and slow discharges. You select the number of cells from a second bank of DIP switches. NOTE: it is important to have one, and only one, of these cell-count selection switches closed or a battery could be drained much further than intended. In reality, the combination of the two sets of switches sets a specific value for the cutoff voltage. This is useful if you want to discharge a pack with a number of cells not directly supported with its own switch (a 5 or 9 cell pack on the PD-12V), or a lithium pack. For example, you can set the PD-12V to discharge a 2s lithium pack to 6.0V by selecting 6 cells and 1.0V per cell. For a 3s pack, you can set the unit for a 9.0V cutoff by selecting 0.9V per cell and 10 cells. A table showing all the combinations of cell-count and V/per cell that you can get for nickel packs from 4-10 cells is on CamLight’s site here. On the side opposite the cell-count and cutoff switches, a third set of DIP switches selects the discharge rate for the high-rate first discharge stage. There are four choices, selected by switching in 0, 1, 2 or 3 banks of resistors. The actual discharge rate is a function of the voltage. There is a table in the manual showing the resulting discharge rates for each of the four possible load settings, for each of the cell-counts settings. The LM-12V Load Module looks like a smaller version (just over 3 inches on a side) of the PD-12V, complete with its own fan. However, it has no control switches and only one LED. This LED lights when the Load Module is active, during Stage 1 of the discharge. A short, stout lead with a latching connector that mates with the jack on the PD-12V comes off of one edge of the Load Module’s board. When the load module is plugged into its socket, then the stage 1 discharge rate ranges from 6A for 5 cells to 12A for 10 cells IN ADDITION TO the values in the table in the PD-12V instructions. For example, with a ten-cell pack, with one of the PD-12V’s load switches down the initial discharge current is 15A, and with four of them down it is nearly 20A.
Both the PD-12V and the LM-12V are powered by the battery being discharged, including the cooling fans on top. Those fans, by the way, vary in speed as the voltage of the battery being discharged changes. This is normal. The current draw when not discharging is less than 10 mA from the PD-12V.
To prepare the PD-12V for use all you need to do is install a battery connector that mates with the packs you intend to discharge with the unit. I put on a pair of Anderson Powerpoles. The Load Module is completely ready to use right out of the box.
Using It
Using the PD-12V is pretty straightforward. Simply select the appropriate cell-count and cutoff voltage combination with the two sets of DIP switches for this purpose. Then select the first stage discharge rate (0, 1, 2, or all 3 switches “on”) that most suits the battery and how it is used.
Then, plug the battery into the input of the PD-12V. If the LEDs light up red then the battery polarity is reversed. If this happens, unplug things right away. Once the battery is properly connected, push the start button. The process from there is automatic.
Initially both LEDs on the PD-12V will light in green, indicating the high-current stage 1 discharge. When the battery’s voltage falls to the cutoff level selected by the combination of the cell-count and per-volt switches, one LED will go out, indicating the beginning of the low-current stage 2 discharge. This proceeds again to the selected cutoff, then the remaining LED goes out, the fan stops and the unit shuts down. At this point the battery should be disconnected. Let the discharger (and load module, if used) cool for a bit before putting away. Remember that they’ve just used all of the tested battery’s energy to help heat your work area.
That’s about it – quick and simple.
Watching and capturing what’s going on with the Medusa Power Analyzer Plus
As John described up above, one can observe the action of the the PD-12V by putting a multi-function meter such as an Astro Flight Whatt Meter or an RC Electronics Watt’s Up between the battery being discharged and the PD-12V. Watching the display gives a good idea of what’s going on and can give you the total capacity drained from the battery (and in the case of the Watt’s Up the maximum discharge current and minimum voltage the battery reached during the process as well).
But if you want to see what’s going on in graphical form and save the data for future reference, putting a Medusa Products Power Analyzer Plus between the battery and the PD-12V lets you capture and display the information on your Windows PC. What follows are some interesting battery discharge examples, captured by my Power Analyzer Plus. This first series shows four cycles of a 7 cell pack of matched Sanyo RC2400 NiCds that had been sitting, unused, for well over a year. You can see that initially the battery (which was fast charged on my Astro 110D after this disuse) delivered less than half it’s rated capacity. After re-reading some of CamLight’s information, I did slow charges (about C/2 with a C/20 trickle overnight) between cycle 2 and 3, and again between 3 and 4. The difference is dramatic, especially in the high-current portion between cycles 3 and 4. While this battery is still not delivering its full rated capacity, it’s going in the right direction and if I were planning to fly the plane this battery goes in soon, I’d do another couple of cycles to see if I could get the battery all the way back up.
Here is an example using the Load Module. This is a discharge of a 3s Tanic 1500 mAh lithium-polymer battery at a discharge current of about 14.5A or very nearly 10C. This particular pack has been in pretty regular use, primarily in my Mountain Models SmoothE, where full throttle currents seldom exceed 12A. From this graph it is clear the battery is capable of giving more than I’ve been asking of it.
Now here’s an interesting one. This is one cycle of a 7 cell Sanyo RC3000H pack that has also been sitting for some time. Clearly this pack has at least one bad cell as it delivers barely 7V initially under a 9A load, yet its capacity isn’t that far off the label rating. Also interesting to me was the rise in voltage during the first discharge stage as the pack warmed up from the discharge action. We expect to see this from lithium batteries, and we knew that NiMHs worked better when warm. Now it is clear looking at that voltage graph.
The bottom line
The CamLight PD-12V discharger is a very useful tool for maintaining your nickel-based drive batteries. In conjunction with a charger you already have it can be used to test, condition and recondition packs quickly and automatically. With the addition of the LM-12V load module you can push packs harder during testing, getting a more realistic view of their performance under actual use, but without stirring up a huge breeze in your workshop (or overheating motors) running your power systems. In fact the system combining both the discharger and the load module can handle over 200W of discharge power.
An even better combination, though, is to use the CamLight dischargers in conjunction with the Medusa Power Analyzer Plus. With this combination, all sorts of interesting data can be seen and captured, along with the enhanced battery maintenance benefits of the dischargers by themselves. Not only can packs be cycled and revived after neglect, but new nickel-based batteries can be characterized, as can lithium-based batteries. I know I’ll be using these tools, especially together, quite a bit in the future. |
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Thread Tools |
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Mar 29, 2005, 04:27 PM
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#2 |
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Registered User
 
Join Date: Jan 2001
Location: Auburn, Washington USA
Posts: 12,751
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Here's a family of curves on the new Kokam 2000 HDR cells done with this test setup. http://www.rcgroups.com/forums/showp...88&postcount=9
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Apr 01, 2005, 10:48 PM
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#3 |
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CamLight Systems
Join Date: Oct 2003
Location: New York City, USA
Posts: 1,151
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And if anyone has any questions regarding our products or their use, please feel free to ask.
 John Muchow Managing Partner CamLight Systems |
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May 12, 2008, 10:16 AM
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#4 |
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Karma is Cumulative
 Join Date: Dec 2006
Location: Seattle, WA
Posts: 1,845
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I'll bump this thread back from the dead - what is the maximum supported discharge rate for 3S lipos of your highest rated system and what system components would be required? Any new products in the works (or released since '05) that support multiple lipo modes?
- David |
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May 12, 2008, 03:50 PM
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#5 |
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CamLight Systems
Join Date: Oct 2003
Location: New York City, USA
Posts: 1,151
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David,
We have several products that can easily achieve 30A-40A for 1S-3S, and lower current levels for up to 10S. These products use a constant-resistance load. During discharge, the current level drops as the pack voltage drops. I'll contact you directly to discuss other options. -- John -- |
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May 12, 2008, 04:41 PM
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#6 |
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Karma is Cumulative
Join Date: Dec 2006
Location: Seattle, WA
Posts: 1,845
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Thanks John! Here's hoping you guys will offer a flexible and reliable solution for high current LiXX discharge to provide some semblance of competition in this nascent and wide-open field.
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