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FMA's Cellpro LiPo Battery Charging System
By Jim Young
Apr 29, 2006, 11:00 AM
Introduction
FMA has always been on the cutting edge of LiPo chargers and protection. Starting with their Balance Pro HD system (review) the engineers at FMA brought a new level of safety and convenience to LiPo charging and discharging for the hobbiest. The Balance Pro HD system is geared toward high power, high cell count systems. Now, with the Cellpro system FMA offers a lower cost system for lower cell count, with all of the safety features of the Balance Pro HD. The Cellpro system is designed for battery packs from 1S to 4S and up to 3200mAh. A lighter connector system allows discharge protection for even small models.
Cellpro Packs and the Pack Node Connector
The Cellpro system is based around a standard 5 pin connector. Whether you have a 2S or a 4S pack, they all use the same connector and all cell charging/balancing and discharge monitoring is done through this connector. This allows the use of your favorite power connector for hooking a CellPro pack into the power system. The connector is keyed to prevent plugging it in backwards and has a locking feature to prevent it from coming loose in flight or during charging. FMA offers this connector with short pigtail wires for updating old or competitor packs to the Cellpro system. They will also be offering a universal adaptor module that will accept PolyQuest, DuraLite, and Thunderpower tap connectors.
The packs used in this review were a 2S 600mAhr pack and a 3S 2000mAhr pack. All FMA packs have a circuit board for making the electrical connections to the individual cells. This helps stabilize the pack and reduce stress on the cell tabs.
Cellpro 4S charger
There are lots of ways to damage a Lipo pack. We'll look at a few, and how FMA has worked to minimize those. The first way to damage LiPo packs is to over charge them. That is where the Cellpro 4S balancing charger comes in. The 4S charger is a nice compact unit. The unit is built on a single printed circuit board (PCB) and the display is mounted to an aluminum plate. The two are attached together with a few standoffs and the whole unit is protected with heatshrink plastic (it looks like a large ESC!). It comes with heavy gauge input power wires and large clips for hooking it to car battery terminals. The charger is reverse polarity protected, so you don't have to worry about hooking it up backwards. There is a two line LCD display, a mode button, a mating Cellpro connector, and a PC interface connector. Pretty simple.
Before a pack is connected, the Cellpro charger will display "Waiting for Pack". With a pack connected, the display changes to "Checking Voltage". This takes approximately 2 seconds, and then the charger cycles to "FAST CHARGING". At this point, the charger also displays the overall pack voltage and the calculated "fuel level" (more on this later). Pressing the mode button once cycles the display to show the individual cell voltages. Pressing the mode button again displays the capacity added to the pack so far, and the present charge current. Pressing the mode button a third time brings you back to the main display. When the individual cell voltage nears 4.2V, the charger switches to "BALANCING CELLS", and brings all of the cell voltages to within 6mV of each other. Unlike "after-the-fact" pack balancers, the Cellpro charger balances the pack while charging it and never lets an individual cell voltage exceed 4.2V. With after-the-fact balancers, the voltage on one or more cells in the pack could have exceeded 4.2V and this damaged it... so much for balancing! The Cellpro charger can shunt up to 300mA around a cell to keep the voltage under 4.2V. This keeps the charge current higher in the other cells to getting the model back in the air faster. The Cellpro charger actually charges at a bit over 1C, so a completely discharged pack can be recharged in about 50 minutes. If a pack has been over-discharged (0.5V < cell votage < 2.7V), the Cellpro charger has a "LOW VOLT RESTORE" mode. In this mode the charger attempts to slowly bring the cell voltages up to 3.0V. If it can't do this within 5 minutes, an error is displayed. If an individual cell voltage is less than 0.5V it cannot be restored and should be removed from service.
Warning: Technical Stuff Below
Fuel Gauge: When a pack is initially connected to the charger, it automatically determines the state of charge and the capacity of the pack to determine the proper charging current. Programmed into the CellPro charger is the typical discharge curve for LiPo cells. Using the cell voltage and the voltage rise over time, it can determine where on the curve the cell is and thus determine the cell's capacity and state of charge. Based on this automatic capacity detection, FMA has added a very cool "fuel gauge" feature. Give the CellPro 4S charger a few moments with a pack and it will determine the % capacity remaining. I tried several different packs with varying capacities, noting the fuel level at the start of charge and the mAhr's added at the end of charge and it was quite accurate. Adjustable Charge Current: The automatically selected charge current can be over-ridden by holding down the mode button. Doing so will cause the charger to cycle through the maximum charge current settings from 0.25A to 3.0A in 0.25A increments. Once the desired current is displayed, simply release the mode button to select it. The Cellpro can always underride a selected current if it determines that it is too much for a pack to handle. Temperature Safety: Another way to damage LiPo packs is with temperature. At 70F, the breakdown voltage of a LiPo cell is 4.35V. If you exceed this voltage bad things (you don't want to know) start happening. At 32F, the breakdown voltage has dropped to 4.2V. Think about this before you top off LiPo packs at home prior to heading out to that winter fun fly! Taking a fully charged pack from warm to cold will have the same affect as overcharging it. To prevent this from happening to the Cellpro packs, FMA has built in temperature detection into the Cellpro charger. For this feature to be effective, the charger and the pack need to be at or near the same temperature. At lower temperatures, the Cellpro charger reduces the maximum charging voltage for each cell from 4.2V at 70F to 4.1V at 32F. This is one more level of safety the Cellpro charger brings to the game. Anyone who has flown a LiPo powered plane on cold day knows that they need to warm up before they put out their full potential. Temperature plays a big part in LiPo cell capacity, and this needs to be taken into account when charging them. In a 3 cell pack the outer cells may be cool, but the inner one may still be quite hot. This temperature difference affects the capacity of the cells and a typical "one charge current for all" can damage the pack. This is why you need to sufficiently cool down a pack before charging it with one of these type chargers. Since the Cellpro charger monitors and charges all cells individually, there is no danger of over-charging an individual cell, so you can charge you packs right after landing and get back in the air faster. Accuracy: On top of all this, FMA factory calibrates each Cellpro charger to give +/-6mV of accuracy on cell balancing and +/-1% accuracy on the charging current. I talked with the design engineer, and he has built in some pretty cool features into the hardware to make the Cellpro 4S one of the most accurate LiPo chargers available.
Cellpro Discharge Protection Module (DPM)
Another way to damage LiPo packs is to over-discharge them, for that there is the Cellpro DPM. The DPM is a very small device that rides along in the model. Weighing in at about half of a servo, the DPM connects between the ESC and the receiver. A simple, one-time programming procedure sets it up for the radio. Simply power up the system with the throttle at low position and switch #2 on the DPM ON, flip switch #2 off, power down the system, and you are done.
The Cellpro pack is connected to the DPM and it monitors all of the individual cell voltages during flight. If any one cell voltage falls below 3V, the DPM pulses the throttle. As the cell voltage continues to fall, the DPM shuts down the throttle to avoid damaging the cells by over-discharging. You can override the DPM to a point by reducing the throttle on the transmitter and then bringing it back up. The DPM has two cutoff modes (hard and soft) that are selectable via switch #1. There are two versions of the DPM: BEC and Opto. The BEC version allows the ESC with BEC to power the receiver. The opto version isolates the ESC power from the separate receiver power. The DPM does draw about 10mAh from the pack, so you want to make sure to disconnect it after every flight.
LED/Speaker Module
On each DPM there is a tiny, 3 pin connector. The LED/Speaker module plugs into this and provides another level of warning during flight. As the pack voltage starts to fall during flight, the module will flash and sound a warning before the DPM starts to pulse the throttle. This gives a bit more warning to line up for a landing. It is loud enough to be heard at an all electric field, but not above a glow engine.
Cellpro Charge Protection Module (CPM)
If you still want to get some use out of an old LiPo charger, FMA offers the CellPro CPM. The CPM allows you to connect a Cellpro pack to a non-Cellpro charger. Simply connect the CPM to the charger, and then connect a Cellpro pack to the CPM and charge normally. The CPM monitors all of the individual cell voltages and cuts off the charger when any one cell voltage exceeds 4.2V. The CPM does not provide any balancing, but will prevent overcharging (read damaging) the cells. Packs charged with the CPM should be periodically balanced with the Cellpro charger.
Putting it all together
FMA has done a good job of making the Cellpro system as "turn-key" as possible. The 4S charger is very intuitive and easy to use. Since it monitors all of the individual cell voltages and the overall pack voltages, there is no guessing on how many cells it is charging. If something doesn't add up, the 4S will not charge a pack. I have monitored it closely for many charge cycles, and the capacity detection and auto charge current setting have been very accurate. Switching between the 2000mAhr pack and the 600mAhr pack, the 4S never charged either pack at more than a maximum of 1.5C. The fuel gauge feature is very useful at the field. You can plug in any pack and immediately know the state of charge. This is great if you have forgotten if you charged a pack, or want to know how much that last flight used up. The DPM gives an extra level of safety and piece of mind. With it on board the model, you'll know exactly when it is time to land and that you haven't over-discharged a pack. I've flown my 32" span Hughes H-1 with the DPM and didn't notice any difference in flight carrying the extra weight. I had always been flying this plane for 10 to 15 minutes on a 2000mAhr pack. With the DPM keeping an eye on the pack, I now know that this plane is capable of over 24 minutes on a single charge! From what I have observed, the balance between cells in a pack depends on how deeply a pack is discharged. When a pack is only half discharged the cells tended to stay pretty much in balance. However when deeply discharged, there is a wide voltage variations between the cells. This is where the Cellpro 4S charger stays on top and keeps the packs properly balanced.
Conclusion
FMA has put together an excellent system for the low power electric flyer. The advanced features of the Cellpro 4S charger add a new degree of safety to charging LiPo packs. Further, the 4S treats the packs very gently to help ensure long life. The DPM module is the only device of it's kind. The small 0.26oz. weight is a small price to pay for additional protection that is offers. I've been flying with a DPM in a few other planes and it gives me piece of mind knowing that I can use all that extra power available from LiPo's without damaging the pack. FMA knows that everyone has their favorite LiPo packs and cells, and they are making it easy to adapt them to the Cellpro system. This is a step in the right direction to increasing the overall safety of handling and flying with LiPo batteries. |
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May 04, 2006, 01:06 PM
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#2 |
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Hold my beer and watch this!
Join Date: Oct 2005
Location: Northern IL
Posts: 2,373
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Jim: Great job on that review. I like to see high quality reviews like this, as it tends to raise the bar for the other reviewers. (I try to be thorough as well)
I just checked FMAs website, and see that they're selling for only $70; that's not too bad. Tip to FMA: in the next iteration of this charger, adapt to to also work with Ni chemistry packs. The fuel gauge feature seems very useful. The DPMs are a great idea as well, as it allows the user to use LiPos with ESCs that are not LiPo-aware. I'm running one myself, and I usually end up under-utilizing the pack as a precaution. Did you find any drawbacks?? Come on, there must be something. Drawbacks, even minor ones, give a review more credibility. I have just switched all my LiPos over to the PolyQuest/Hyperion balance taps. Is it feasible to cut off the Cellpro connector from the charger and replace it with a PolyQuest/Hyperion tap, rather than buy all those CellPro taps and rewire my batteries again? I'm thinking of buying a back-up charger for my Multiplex LN5014, and this one is about $30 higher than was I was looking at previously, but I'm still considering it. Anyhow, good job with the review. Thanks for being one of the guys who keeps the bar high. 
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May 04, 2006, 04:39 PM
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#3 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,259
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Hi Jeremy,
Thanks for the kind words, it is easy to write about a good product. I have several older ESCs that I use regularly, so the DPM is a great way to get the most out of a pack. I like this better than the overall cutoff voltage built into newer ESCs since it will catch a weak cell. I would like to see some ESC suppliers build the DPM feature into their ESC, and thus eliminate the DPM. Drawbacks?hummm... The packaging is kind of cheesy with the ends open and the PCB exposed. I worry a bit about a nut or screw getting in the charger and causing a short. But I understand that there are other chargers out there with this construction and this does help keep costs down. You might complain that FMA only offers Kokams for now, but they are very willing to sell you a pig tail to convert your favorite park. When you get down to it, this charger charges faster, is basically fool proof (you don't need to watch over it to make sure it guessed the right number of cells or that you didn't bump the current knob too high), balances on the fly (no additional balancing module required), displays all voltages and currents, and allows for any type of power connector. What more could you want or need? FMA offers an adapter module for the Cellpro (and Balance Pro?) chargers that will accept most other brand's tap connectors. So, you don't need to replace all your taps. You will not be able to use a DPM without changing the connectors. -Jim |
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May 11, 2006, 07:46 PM
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#4 |
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know it all
Join Date: Nov 2003
Location: Miami, Fl
Posts: 2,958
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Now if the Balance pro had an lcd display and that nifty fuel gage function, everything would be perfect
 Herm |
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May 12, 2006, 06:39 AM
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#5 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,259
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I'll second that, It's a pain lugging my laptop to the field!
-Jim |
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Jun 16, 2006, 01:34 PM
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#6 | |
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"No, I'm not too old"
Join Date: Feb 2006
Location: Indianapolis, Indiana
Posts: 342
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Best Lipo charger?
Quote:
If you don't have one of these, get one you will not be disappointed. I think the best feature (among all of them) is the remaining Fuel supply, it tells you how well you actually are discharging your cells. When my helicopter won't hover, it is time to land. I find my cells are discharged to about 10-20% fuel remaining. 
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Jul 03, 2006, 07:57 PM
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#7 |
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Hotep
Join Date: Dec 2005
Location: UK
Posts: 2,352
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Hye guys, I'v only just heard of this charger and just in time as I was just gonna order another charger.
I have question How can I connect FlightPower Evo 20 Lipos to this charger, the FP lipo's have a 4 wire balance plug on them, and fits the Align charger. I thought I would be able to use this but i rang a online store today and they say it wouldn't fit... but I'm wondering if they're wrong, because looking at a blown up pic the middle female on bottom row looks the same.. So do any of u guys have any info for me ? I dont really want to change all the plugs on my lipo'. Thx
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Jul 04, 2006, 07:16 AM
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#8 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,259
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Hi Shu,
FMA is putting out a "universal" adaptor module that accepts most current balancing connectors and gets them into one of their chargers. I know they had prototypes at Toledo, and they should be in production by now. The other option is you can buy a CellPro pigtail for about $2.00, then you just need the mate to your pack's connectors and build a short harness yourself. -Jim |
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Jul 04, 2006, 09:35 AM
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#9 |
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Hotep
Join Date: Dec 2005
Location: UK
Posts: 2,352
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Thx for that info Jim Young.
So the "This" llink I posted above is not the "universal" adaptor module" that you are speaking about ? Hmm so I can get that when it comes out and in the mean time make one up my-self.... so I'd just need their pigTail thing and a 4-pin-female-connecter that fits my lipos, well thats fine for me, I wonder where I can get one from ? anyone know ? I wonder if I can get one from an old pc-mother board ? I want this charger ! 
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Jul 04, 2006, 04:19 PM
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#10 | |
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"No, I'm not too old"
Join Date: Feb 2006
Location: Indianapolis, Indiana
Posts: 342
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Lipo Adapter harness
Quote:
 . I just ended up buying their pigtail and then finding the correct connector for my battery pack.My suggestion would be TV, DVD, VHS repair shops, get an old board and find that female connector. I found mine off an old copy machine board  .You will love this charger.
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Jul 04, 2006, 08:20 PM
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#11 |
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Hotep
Join Date: Dec 2005
Location: UK
Posts: 2,352
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Thx ritzheli Its good to from someone who's done this, I think I'll order tomorrow.
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Jul 05, 2006, 06:43 AM
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#12 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,259
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Hi Shu,
Yes, the link you posted is the adaptor I was talking about. I guess it only does PolyQuest and TP packs. Everyone is coming up with their own tap connectors so its hard to keep up with all of the connectors. I would suggest you also try Digi-Key and Mouser for the mating connector to your packs. Try a post in the Battery forum to see if anyone else has found a source for it. -Jim |
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Jul 05, 2006, 07:06 AM
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#13 |
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Hotep
Join Date: Dec 2005
Location: UK
Posts: 2,352
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Ok, Jim, will do, thx again.
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Jul 06, 2006, 07:29 PM
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#14 |
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Hotep
Join Date: Dec 2005
Location: UK
Posts: 2,352
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Well it came today & I love it so much I had to make a thread on it.
http://www.rcgroups.com/forums/showthread.php?t=539594 Thx again Jim for the info. |
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Jul 09, 2006, 08:00 PM
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#15 |
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Registered User
Join Date: Jul 2006
Posts: 1
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I'm new to lipo batteries and chargers. I have a few questions about the Cellpro Charging System. I'm looking to find something on the not-so-expensive side, but I mainly want to purchase a good lipo charger that is capable of cell-balancing (either through an intermediary device like the Great Planes Equinox Cell Balancer, or directly built-in into the charger), and a way to charge indoors from a 110 volt AC wall outlet.
1. Can the charger be hooked up to any sort of AC power supply unit? Or do I have to attach those large clips to car battery terminals? I guess I don't understand the reasoning behind only allowing to charge from a car battery. 2. What is everyone's opinion of the DPM? Are there competing products that are for use during flight-time? For an electric-flight newbie, is it a good idea to purchase the DPM? I definitely want to protect the cells from damage as best I can. 3. Are the Kokum/CellPro lipo packs best to use with the CellPro charger? I'd really like to hear as many opinions about this as I can. If anyone has any links to good battery/charger/PSU reviews or articles, I'd really appreciate them. I'm looking for as much info about batteries/chargers as I can. I want to make a good decision. Thank y'all! David |
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