madpogue 

Light is a VistaLite VL-420 (two of 'em, actually); it uses a 6V, 2.5AH Sealed Lead battery. It's made from three 2V, 2.5AH D-cell format cells, with soldered leads, wired together in series, with a coax plug that goes into the light. The charger is just a wall-wart that plugs right into the battery wire.

The batteries will no longer take a charge. Between the two battery packs, there aren't three cells that each charge to a full 2V, so I can't frankenstein one good pack out of the two. I'm considering alternatives to simply buying new SLA batteries (or buying the single cells and rebuilding them), in part because I'd rather buy something more environmentally cool than batteries full of lead.

Here are the choices I'm considering:

1. Get or make a battery holder, and buy four (or five, if they're 1.2V) NiMH AA batteries in the 2.0-4.0 AH range. Wire the battery holder to a coax plug to plug into the light. Charge the batteries in my existing AA NiMH charger.
2. Buy four or five NiMH batteries, with tabbed contacts, in any format that will fit, in the 2.0-4.0 AH range. Build a battery pack with the coax plug. Charge it using the wall-wart charger that came with the light.
3. Status quo. Break down and buy (or build) a SLB pack, and charge it with the wall-wart.

Questions:

• For option 1, I've found a really good deal on 2.0AH AA's. But since the original battery was rated 2.5AH, what will be the implications? AFAIK, it will simply mean the life per charge will be about 20% less, right? At 6V, it'll be just as bright, right? One advantage of this option, too, is that the batteries will be interchangeable with my digital camera, my existing Planet Bike headlights, my police scanner, etc.
• For option 2, Will the wall-wart charger properly charge the NiMH batteries? Does anybody know about the charging characteristics of NiMH batteries, compared to SLB's? I don't think the wall-wart has any faincy 'lectronics in it to detect the charge level of the battery it's charging (or am I wrong?).
• Generally, does physical size matter? (Of the battery!) I mean, if I put together five 1.2V, 4AH AA cells in series, I'll have a 6V 4AH battery pack, with the same per-charge life of any 6V 4AH battery, right? And generally, do I multiply charge (AH) if I connect in parallel? I was thinking of putting 10 2AH AA's together, that is, a series-pack of five, in parallel with another series-pack of five. Does that sound right? Or should I make five little packs, each consisting of two in parallel, and string them together in series with each other?

Any other ideas?

Jay H

Check out Section 4 of this:

https://user.fundy.net/cyclist/bikecurrent-FAQ.html

And also this on NiMH chargers:



I'm also in the process of considering making another 8ampHR NIMH for my set of Marwi lights. The Marwis that I have is a 6V 12W/20W dual so I should get around 4 hrs of light using just the 12W spot when I commute. I'd also like to get a better charger than the charger that comes with the unit, from the FAQ, it seems to say that it can lead to overcharging which is bad for NiCADs/NIMHs...

Link

Jay

madpogue 

From the bikecurrent FAQ:Ah, so that's why the SLB packs I have now will no longer hold a charge. Now you tell me (sigh).

At least I know what to do with those wall-warts (looking for a door that needs propped), and what charging method to go with. Fortunately, my two NiMH chargers are "smart" chargers; I haven't had any problems with leaving batteries in them past the full charge. Now, I just wonder if a four-block of AA NiMHs will produce the proper voltage, or should I get a six-block battery holder, and put five in (for a true six volts), and jumper the last position. Hmm, hmm....

Great links, btw; thanks!

Jay H

Well, most of the AA NiMH batteries are 1.2v so you would need 5 of them to get 6v. That link seems to imply to get 8ampHR, you can't simply add the aH ratings of the individual cells either, i.e. 5 2100mAH batteries doesn't equal 10.5aH, but then again, I haven't read the whole electronics speal yet.

I wonder if we can simply buy the largest mAH ratings given the 6V lightbulbs we both have, why would we be limited to using AA NiMH batteries or so, since some of the larger NiMH batteries seem to have a higher amp hour rating..

Anyway, I'm going to be looking at those files more too...

Jay

madpogue 

As I understand it (and it jives with what I remember from physics class in high school back in the last century), you add voltage (V) as you connect batteries in series, and you add charge (AH) as you connect in parallel, provided the batteries are of the same voltage. There was some talk on that page of putting in some 'lectronic thing to even out the voltage and charge of batteries connected in parallel, but it was looking kinda confusing. I'm gonna stick with a series pack.

The reason I'm relegating myself to AA's is that I already have two AA NiMH chargers. And rather than trying to combine batteries in parallel to increase run time, I'm just gonna carry a spare set of cells (same number of batteries), and use a battery holder as the power pack, so I can just pop cells in and out as I need.

uciflylow

I build battrie packs for my model airplanes all the time. The mAh rating is for the cell, add the individual cell voltage togather in series to get pack voltage, but the Ahr rating stays the same. You can get subC cells that go to around 2000 mAh, and D cells that go higher. If you want to go the route of NiMh, I suggest you get a charger designed to a delta peak sensor, or heat sensor for charging. Learn how to program a charger, charge rate X cell +the Delta per cell you want your cut off, and you can expect packs to last a long time.

One other thing I might add. NiMh and NiCad can be fast charger. Lead acid can not. NiCads are more forgiving and have a wider fudge factor than NiMh, but NiMh are lighter. If you want to use a pack type holder I think you can buy a battrie charger at Radio Shack and take the individual cells out of the holder and charge as individuals. You could try and find a source for a 6V individual SLA battrie, like a cam corder battrie, and use this. Instead of leaving the walwart charger pluged in all the time. Set up a light timer on an extension cord so it only comes on for say 1 hr a day after the initial charge. In other words, set up a 24 hr timer to come on once a day, for one hour. This will keep your pack ready to go, and not dammage your pack by over charging.

Jay H

Aha, so if I wanted to similate my 8amphr 6V NiMH battery I can put around 4 "packs" of 5 1.2v 2100mAH AA NiMH batteries in parallel and that would be roughly 8.4ampHr 6V battery, right?

Oh, and that is a good idea with the timer, I've emailed Marwi about their walwart, but I gather it's only a stupid transformer and not really a smart charger. It is a slow charger, designed for a 20hr full charge on the 8amphr battery. I like the timer idea and going to try to see if I can build/buy an inexpensive smart charger.

Jay

madpogue 

Jay, if it's a wall-wart, it's most likely just dumb DC power. That's certainly the case with the Vistalite charger, and that's why my SLB's are history. If you're thinking of using AA's because you already have a AA NiMH charger, you can simply set up a single 5-cell pack using battery holders (4 + 1, or 3 + 2), carry all 20 cells, and as a set goes yellow, pop in a new set of 5. In effect, your run time is in "sequence". This is what I'm gonna do, so I don't have to go out and buy a 6V smart NiMH charger. If you're planning on building "permanent" packs and buying a 6V charger, there are C and D format cells that have from 4 to 8 AH charge, so you don't have to parallel so many together.

Batteryspace.com has some pretty good prices on NiMH cells of various kinds. Here's what I've found that might be of interest:

10 C-size 4AH cells, with tabs (so you can solder 'em up for a pack) $23
https://www.batteryspace.com/product.asp?3=167
Make two sets of five, in series, connect the two sets in parallel, and you've got 8AH x 6V.

Two 6V 4AH packs, each built from 5 C-cells, with a connector, $22
https://www.batteryspace.com/product....17&1=227&3=169
Splice the two sets of wires together in parallel for 8AH, or run each one in "time sequence". Come to think of it, this is actually a better deal, since it's a buck less, and it's already built up for you.

Smart charger for any 6-10V battery pack, $30
https://www.batteryspace.com/product....08&1=337&3=353
Looks like it has the connector (or adaptor) that would work with the pre-made pack above.

If you're going with indiv. AA's:
24 AA 2AH NiMH's, $25
https://www.batteryspace.com/product....17&1=285&3=246
About a buck a cell!

24 AA 2250mAH NiMH's, $34
https://www.batteryspace.com/product....17&1=285&3=389
More run time, but more dollars per charge time than above

I've seen mainstream brand (Ray-o-vac, etc) NiMH not-fast AA/AAA chargers for as little as $10 after rebate, and they often throw in two cells. I've even seen such chargers thrown in as "bonus" items with digital cameras, et. al. on eBay.

I found out on the batteryspace forum that to get the true, full 6V to replicate the voltage supplied by a 6V SLB pack, yes, you need five cells. For many applications, the lower voltage (1.2V vs 1.5) of NiMH's is not relevant; for example, in a digital camera, a set of four 1.5V alkalines quickly drop to about 1.3V per cell anyway, early on in their use cycle. Fully charged NiMH's actually run about 1.3V, so it's a wash. So 4 1.2V NiMH's work just fine in a "6V" device such as a digital camera.

But SLB batteries keep their voltage; a charged 6V SLB pack will stay at a little over 6V until about 75% discharged. To emulate this, you need that fifth cell to get the voltage up to a true >6V.

Note: I have no association with batteryspace, I just found their prices to be good, compared to other "bulk" battery suppliers, and they were prompt in answering my voltage question on their forums.

I now know more about all this stuff than I ever wanted to...

madpogue 

I just got another reply on batteryspace. Apparently it's better to gang the 6V strings in parallel, than to run each one in "time sequence". Here's his post:

Jay H

Thanks for that link, I'm definitely going to buy that charger, sounds like a good investment, I'll just hack off the connector off the one that Marwi provided and splice the +/- connectors to it and I should be good to go.

Then I'll just take the water bottle (or make one out of a spare) of my existing dead Marwi battery and then use that as the shell. I'm just wondering if we need to do the diode thing for packs in parallel, the fuse should be easy enough to do.

[edit ]- I'm checking out those forums at batteryspace, it appears that they do not recommend wiring batteries in parralel, not for discharging but for charging purposes. So I looked at those battery packs they sell here:

https://www.batteryspace.com/product....17&1=227&3=169

(Same link as above) and with my 6V 12W light, which draws 2amps, I should get 2 hours of lighting with one pack.

That should last me 2.5 commutes in winter (to be safe, consider it 2 commutes) and with that 6V-10V universal NiMH charger, I should have two working battery systems pretty much for $60 with of course misc wire and fuses.

If one is really ambitious, one could make some regular battery holders so you don't need to buy the tabbed cells which are more expensive and then wire them up in parallel but removable so they can be charged with a smart charger individually, which would avoid the problem of charging battery packs in parallel.

Jay

Bluechip

Keep this thread up to date with your progress. I bought the same batteries and charger from them and would like to know the best way to proceed. I am a complete elctrical novice so any guidance would be appreciated. The batteries came last week and I am still waiting on the charger. I was surprised to find the batteris so small and light. They can fit the into an old waterbottle but rather snugly.

madpogue 

Actually, it looks like the charger on batteryspace has a connector to match the connectors on the packs we both found. So what I'd do is make a y-cable, with two connectors that "mate" the ones on the battery pack, and one connector that "mates" the connector on the light. Then you can charge each pack separately (not in parallel), but connect 'em in parallel with the y-adaptor to the light. If you can get those two packs to fit inside a water bottle (cut off the bottom, maybe?), so much the better. Remember, it's okay to discharge (use) batteries in parallel, as long as they're the same voltage. The neat thing is, in a pinch, you can use just one (while you're charging the other, for example); it'll just have a shorter run time.

That's exactly what I'm doing, but mostly since I already have a coupla AA NiMH chargers (for my existing Planet Bike headlights, and my digital camera). Again, the neat thing is, once I build the packs up, I can run with 10 cells or just five, depending on how much run time I need. The impression I got from the guy who responded on the batteryspace forum was that having parallel batteries at run time gives you something of a "buffer".

madpogue 

The important thing to keep in mind is that it's okay (in some ways preferred) to run the batteries in parallel, but you must charge them separately. So if you plan to run them in parallel, you need some way to connect them to the light simultaneously, but connect them to the charger separately. Thus my suggestion of a y-cable in my last post.

About the weight, that's the BIG advantage of NiMH. I looked around a little more this morning, and found some SLB UPS batteries that might actually fit the bill, even size-wise. They're actually cheaper per unit of total energy (watt-hour) than NiMH's. But d@mn, they're heavy! I'm glad I'm going with NiMH. Plus, lead is not the most environmentally cool thing to be lugging around on your commute each day.

Jay H

Well, I emailed batteryspace and they responded saying that the battery charger will fit the connector on the 6v battery pack that they sell. I also checked the dimensions of each pack, 2.5" x 2.5" x 2" and it looks like it might fit in a water bottle as my diameter on my water bottle is about 2.75" so it looks perfect.

I also asked them about the weight, it's 14.45 ounces per pack so both packs would be about ~1.75 lbs themselves.

Jay

slvoid

Nimh AA's are now up to 2400mah with 2600mah's right around the corner. At this rate, they'll eclipse a standard 2800mah alkaline AA battery in a few years.

Rather than make it a waterbottle battery again (which takes up a cage) why can't it be a long tube that you can velcro to the frame?

Jay H

Sure, you could make it into a tube, but not with the battery "packs" that I am thinking of buying because they are square. (You can see a picture of it through the link). If you were to use AA batteries, then why not. I do believe the Vistalites use a stick they call the "Code Stick" or something like that, I've seen pictures of them at STP.

Jay

slvoid

Yes, in fact, I think theirs is basically a bike pump housing with batteries in it and mounts to the side of the bottle cage.

madpogue 

Batteryspace discount alert! Don't order from them yet! Before I prattle on about building the pack, check this out: When you order, one of the pages that you go thru has a fill-in for "coupon code" or "discount code" or some such. Just type in "batteryspace", and poof!, it knocks 5% off the pre-shipping total. Sorry I didn't post this earlier, for anybody who's already ordered. Hey, maybe they'll let you take it off after the fact...

Now, back to our regularly scheduled prattle...

It's done! I bought two 4xAA covered holders, plus one 2xAA, at Radio Shack. 'Course, the problem was, the 2xAA is, like most, a series holder, so I still didn't have 5+5. So I hacked it. I removed the "crossover" terminal bar (the one that connects the positive post of one battery to the negative on the other), and broke it in two. I made sure to break off a bit of the metal in the middle, so the two would never touch. Then I drilled some new holes in the housing, soldered wires on the two pieces of terminal that I had just busted, and put them back in place. So now that 2x is really two singles.

Why? 'Cuz RS doesn't carry a covered single AA holder. Nobody makes a 5x. I saw some 3x'ers on the 'net, which I could have put in series with a 2x, but they weren't covered, and shipping for such a wimpy little order woulda been a killer.

So I put the two 4x'ers back to back, and the 2x on one end of that assembly, using double-face tape and duct tape. Series wired each 4x'er to the two singles that I created, then parallel connected the two strings to the wire that I resurrected from the shot SLB pack. I was hoping to do the extreme hopeless geek tweak and heat shrink all the wiring, but alas, I couldn't find the stuff. So I just soldered and e-taped all the connections. Total part cost: about $5. Assembly time: coupla hours, given I was watching TV at the same time.

The enclosed holders are nice. Yeah, the whole thing sits in a little nylon pouch that hangs on the frame, but the enclosed holders offer more weather protection. And I don't have to worry about cells popping out on bumps, etc.

The whole thing takes up about as much space, and weighs a whole lot less, than the 2.5AH SLB pack. And with the parallel connection, and the 2AH batteries on order from batteryspace, this pack has a 4AH capacity. Should give me 4 hrs run time on this bulb. If I choose to put in a 10W bulb, I'll probably get 2-2.5 hrs run time. Sweet!

Here's a weird thing. The 4x holders have switches. When I switch either one off (or pull a battery out of either string), I'm effectively running on just one string. But the voltage should remain the same, right? Well, the light dims just ever so slightly. Thinking that it's one string having slightly higher voltage than the other, I switched it back on, and switched off the other string. Same effect. I checked the voltage with either string on and both strings on. It's always 6.45V. So for some reason, having more charge allows the bulb to draw more, and burn brighter.

I'd post pics, but my digital camera is shot (dropped it on a tile men's room floor last weekend; don't ask).

Jay H

Not an expert but as long as the voltages are the same, the total voltage should be the same whether it's just one pack in series or a bunch of packs in parallel. What you could be witnessing when running packs in parallel is simply a redundancy between each pack that is in parallel. The light will simply draw power from the "best" pack that is connected in parallel. Perhaps the pack that you are switching on is slightly more charged than the one you are currently running. You say that when you switch the second pack on, the light gets brighter. What you can try is do the opposite, connect only the second light to the light bulb and then switch the first one connected in parallel and see if the light remains the same.

Then you can assume that the second pack has more charge.

Of course, I could be all wrong.
Jay

madpogue 

Well,as I said, the brightness is the same with either single pack. It's just a little brighter with both. Nothing consequential, of course, just something for my morbid curiosity.

Jay H

So, I took my old Marwi 8aH 6v battery apart and I can now say with authority that the cells in there are toast. They're spilling their guts out and are definitely toast. It appears to by 2 packs of 5 1.2v cells in parallel for a total of 10 batteries. The cells themselves are green with no writing on them, however what I found interesting is that there is a small silver thingajig wired in series, one on each pack which I can't tell what it is, a fuse or a diode? It's a really small silver rectangular box that has the line "PEPI N" on one flat side and on one of the edges says "J020+120" whatever that means... I would think that J is usually a schematic for some kind of jumper and the 020 would be an identifier but don't think that's right. Anybody have a clue what it is?

What do you also know about charging NiMH batteries connected in parallel, I'm told it's a bad idea, however the charger provided can only charge them in parallel. Which is why I really want to build my own, something that I can build that can be charged as an individual pack and then connected in parallel for use. But what are those little silver things? What do they do and I'm wondering whether I should recreate that... Anybody know?

Further interest is that the cells don't appear to be standard AA size, they are about 12mm longer and about 2-3mm larger in diameter..

Jay