Electronics, Lighting, & Gadgets - DIY Battery Pack for MS 900?
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02-01-11, 01:21 PM
I need a new headlight and want to go for something more than a 'be-seen' light. After doing some searching and some reading, I think the MagicShine 900 fits what I want (no proprietary batteries, nice and bright, low price).
However, I'm a little wary of any of the pre-built packs being sold with it by various people, so I'm interested in putting together my own pack so I can charge the cells separately (to avoid problems with them becoming unbalanced). What brands and suppliers should I look at for the batteries, for the charger, and for the holder? I'm not sure what's a good compromise between cheap and not junk. Oh, and for the first round I'd like something I can get faster than DX, or preferably any of the other HK dealers. I don't want to wait that long to be able to ride in the dark, after work.
Also, I'm not new to electronics and soldering and such, but I've never build a battery pack before. Are there any special considerations I need to know about? (For instance, if I go with unprotected cells, what extra precautions do I need?)
Finally, someone else said this (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-024A-ND) was the right part to mate with the connector on the MS. Is that right?
Thanks for any help!
02-01-11, 01:57 PM
That's not quite the right connector, the right one has a water shield which also holds it together. Best thing to do is to order a couple of 1M extension cables along with the light, and cannibalize them for connectors. DX sells a Y adaptor with two of the right connectors on it for < $4 so it's even cheaper.
I use a Tenergy 8 cell pack, but if you really wanna build your own, try this and 4 18650 cells
Then you can charge the whole pack most of the time, and pull the cells out to charge them individually once in a while to rebalance the pack.
02-01-11, 02:22 PM
If you dont have a charger or anything else to start with, you'd be hard pressed to build a pack for the price of some of these from this RC place. (http://www.ballisticbatteries.com/Page.cfm?Category2=Magic%20Shine%20Batteries&InfoID=200&Search=)
The BatterySpace holder will work well as a hybrid (pack charge or cell charge) being prewired and including a PCB, most of the key things are done for you. However, protected cells will not fit. It is meant for unprotected, flat top cells so the cells you may have sitting around for flashlights etc probably wont fit. On the occasions you cell charge unprotected cells, dont leave them unattended.
At the other end of the spectrum is the Luminous holder (http://www.luminousdiy.com/Light%20Kits%20and%20Parts.htm#holders). These come as 'blanks' with battery contacts that you wire however you need (4p, 2s2P etc). They will hold any cell, but unprotected are a little loose which can be secured with a velcro strap. There is no PCB so you are supposed to remove the cells and charge in a cell charger. There are some pictures in this thread (http://www.bikeforums.net/showthread.php/709643-Geo-Update-Late-April-ETA-for-new-packs/page2).
02-01-11, 04:30 PM
Thanks for the suggestions. They make sense. Plutonix, would you recommend getting a pack rather than separate cells, then? I mostly wanted to get individual cells so that I could rebalance them from time to time; I'd gotten the impression that that was helpful (or even important, if you wanted to try cheap cells). But, like I said, I don't actually know! I haven't built a battery pack before.
Also, I see some 18650 cells for $4 each, and some for $10+ each. What are the tradeoffs? Where do you all prefer to get yours, excluding (for now) DX because of the unpredictable lead time?
02-01-11, 05:13 PM
I've been thinking of the same idea and my understanding is that if you charge any batteries in series (eg 2S1P or 2S2P or 2S4P, etc) there in nothing to stop any 2 batteries in a 2S pair from becoming unbalanced. Using 'good' cells reduces the odds of problems since these cells are supposed to be more closely matched. BUT, you are still charging them 'open loop' in the sense that there is no feedback to signal that they are becoming unbalanced. If one battery loses capacity sooner than the other then the pack becomes useless or even dangerous until the batteries are rebalanced or replaced.
Based on this and magnitude of what can go wrong, etc it just seems much more sensible to have a pack that can be balanced charged occasionally, either by having separate leads coming out of the pack (ugh!) or having removable cells. I'm leaning towards trying to gen up a carrier that I can just plug in for most charges and then easily disassemble every so often to check and re-balance the cells.
02-01-11, 08:12 PM
...Also, I see some 18650 cells for $4 each, and some for $10+ each. What are the tradeoffs? Where do you all prefer to get yours, excluding (for now) DX because of the unpredictable lead time?
...Based on this and magnitude of what can go wrong, etc it just seems much more sensible to have a pack that can be balanced charged occasionally, either by having separate leads coming out of the pack (ugh!) or having removable cells...
If your budget or mind set only allows for $4 cells, you'll probably get a more bang for your buck with the Ballistic packs. I found them from user feedback on an RC board and thats their biz, which made a good impression. I might check what the warranty was. With $5 cells, building your own will cost more than one of those packs and likely not be as good.
Iowegian, either method discussed here will minimize unbalanced packs. The BatterySpace holder (http://www.batteryspace.com/Battery-holder-Li-Ion-18650-Battery-Holder-2S2P-With-2.6-long-20AWG.aspx?SSAID=314743) has a PCB, so you can pack charge it most of the time but do as ItsJustMe said and periodically open it up to balance them with a cell charger. If you are queasy about cell charging unprotected cells you can alternatively discharge the higher voltage pair down to the level of the others using a flashlight.
The LuminousDIY (http://www.luminousdiy.com/) holder/method precludes unbalanced packs because when you charge, you remove the cells and use a cell charger (Do Not use a pack charger - no PCB). Assuming you charge all 4, you are rebalancing each time. The down side is the inconvenience.
The tradeoff with protected vs non is almost irrelevant. The type of pack you build determines which you need: the BS holder requires unprotected, the Luminous ought to have protected. Unprotected choices will be somewhat slim, so just pick one of the ones they list as compatible like the LG 2600s.
There are more options for protected cells in the Luminous holder but most US sources are "premium" cells. Lighthound (http://www.lighthound.com/Li-Ion-Protected-Batteries_c_24.html) sells AWs. The cells the flashlight people are currently nuts over are Redilast but they seem a bit pricey. BS looks to have one protected button top. Most of the rest come from Hong Kong: I used Panasonic 2900s (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390266429165&ssPageName=STRK:MEWAX:IT#ht_2264wt_770) in my Luminous. Trustfire 2400s (http://www.dealextreme.com/p/trustfire-protected-18650-3-7v-true-2400mah-rechargeable-lithium-batteries-2-pack-20392) (flame one) from DX seem consistant and actually around 2400 (the wrappers are very thin and fragile on mine).
By time you allow for a charger, cables and shipping, you can easily spend more than on a pre made pack. The only way to beat it is to use cheap, low quality cells which is part of the problem not the solution. That said, some of it is an initial investment: when the batteries age you can replace them more cheaply than replacing the pack; the charger has other uses; when you get a new light it takes about 10 mins to wire a new connector; the cells are not locked up in the pack and can be used elsewhere as needed.
If you have faith in the coming MS replacement pack, you could also consider 7 AAs in a holder to get you by until April. Economical, if you have AAs laying around.
02-01-11, 11:46 PM
Agreed. My situation is that I already have a 2-cell 18650 charger and a few loose cells (ones recommended by SoCal Rider here) as well as 2 MS packs. Plus, I had a resistor burn out on one of the MS PBCA's when it got slightly wet so if I'd like to have packs that are waterproof. The part I'm having trouble with is how to make a waterproof pack that can be taken apart without a major hassle since the idea of pack charging for the life of the cells doesn't seem optimum to me. I'd like to be able to balance the cells or at least monitor them to see how well they stay in balance. But that requires a pack that can be disassembled. I'm probably over-engineering this thing and should just get a holder and put it in a water bottle but I'd like something that could be mounted on the frame like the MS style pack.
02-02-11, 09:42 AM
I think the BS holder with charger is the best DIY approach for most people since there are fewer occasions to insert a cell backwards and trip the protection or ruin it. If you already have cells and cell chargers to start with though, the Luminous holder can be cheaper to make than buying a pack: $15 plus some wire.
BS has PVC heat shrink pretty cheap, so that holder can be sealed up that way and cut open several times times a year for balancing. Waterproofing and EZ open is tougher with the Luminous because you open it so often. But since there is no PCB to short out/ruin, you mainly want to keep the cell casings from getting water damaged.
The holder fits the 2 strap MS bag, I put a layer of Gorilla Tape on the bottom and sides of the bag to ward off road splash. For more protection, first place the holder in a twist tied baggie. Together, that might be enough for many people for most times of the year.
A cannister of some sort in a bottle cage is cleaner and better but for frame/stem mounting, a gigantic 3.0" inner tubes will work. The Luminous will slide right in and the BS looks like it might fit. Silicone and zip tie one end; maybe zip tie the other using a re-usable zip tie with a release. Or leave enough tube to wrap around the pack 1.5 times - water would have to circle the pack, make multiple turns and go uphill before reaching the cells. Very ghetto and it may not hold up to submersion but seems more than is on many packs.
This is an inner tube case for a different pack, but shows that it just slides in. To use this I would rework the orientation of the connector.
02-11-11, 11:42 AM
Ok... what am I missing... when a 'reputable' battery supplier makes up a pack with (PCB's?) on the batteries is this not essentially a load leveller for the charging of the pack? I.E. would this not make separate charging (impossible anyway) of the batteries in the pack unecessary? Batteryspace makes (and sells) a 4800mah pack bundled with a smartcharger with the correct connector for attaching to a MagicShine. I use this exact system in Oregon. It rains (a lot) in Oregon. Practically submerged there hasn't been so much as a peep from the unshielded connector. FWIW I bought an extra cable from GeoMan to cannibalize (unecessary) and it wasn't shielded either. Wouldn't you rather be out riding than smelling soldering flux fumes? I would (am). FWIW.
02-11-11, 12:10 PM
Ok... what am I missing... when a 'reputable' battery supplier makes up a pack with (PCB's?) on the batteries is this not essentially a load leveller for the charging of the pack? I.E. would this not make separate charging (impossible anyway) of the batteries in the pack unecessary?
It is not impossible that the PCB is acting as a load leveler but I have never seen one advertised as such. If someone was making an 8.4V pack that included circuitry to insure that the batteries in series are equally charged I'd assume they would advertise the feature.
The issue is that the 2 batteries are operated completely in series with no access to the center point. The PCB controls the charge level, charge rate, discharge rate, etc of the 2 batteries - as a pair - but does not monitor the individual cells. So over time, one battery may be running at a higher voltage than the other. All you know is that the sum of the 2 voltages is nominally 8.4V. One could be at 4.0V and one at 4.4V. At some point, one of the batteries can enter an operating region where it will malfunction. Taking the batteries out of the pack and charging them individually will re-balance them and reset the voltage drift process but as you mention, that isn't really an option on many packs.
02-16-11, 12:26 PM
I just opened up one of my packs today to fix a frayed wire and decided to check the cell balance. The pack was at 8.0V but one pair of cells was at 3.88V while the other pair was at 4.11V. Hmm, no wonder it didn't seem to have much capacity anymore. I think I'll take Geoman's advice and put it aside until I can get a replacement.
03-01-11, 07:17 PM
rechargeable flashlight batteries are 1.2V, line them up in series ,
battery holders from Radio shack was what I used , 5=6v
i lined them up and tied them inside my Carradice saddle bag
made light for my Hour commute, 20 years go.[only had NiCad batterys then.. ]
What about using a 2s LiPo? Smallest, lightest, and highest energy/power density solution of all. Also a great excuse to get a proper charger so you really know the health of these and any other batteries you will use in future.
03-02-11, 12:14 PM
http://www.youtube.com/watch?v=SpOx_V4CIZs&feature=player_profilepage......... get the right parts from digicomm
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