I use AA alkaline batteries and am thinking of changeing to rechargeables. I have a bunch of old cell phone(the Brick model) batteries that are just a lot of AA nicads in series. I decided to do a little test. I test the state of my batteries by putting my multi-meter on the 10 amp scale and momentarily touching the battery terminals. A new alkaline will pull about 6 amps. I took my battery pack(4 AA in series) and measured it the same way and I got about 6 amps as I thought I should. I then took 5 of the cell phone nicads and measured each of them. They pulled about 8 amps each, again not a surprise, nicads have lower internal resistance. I put the 5 together in series and measured the pack. Surprise!!!, it pinned the meter hard. My meter only goes to 10 amps so I can’t change scales. Anyway the question is have I found a loophole in one of the laws of physics or what is going on here? If I had them in parallel I could see it but they are in series. Is it the low internal resistance of the nicads that is doing this?
Edit: I know there are better options than old cellphone batteries but I have many of them and a charger and a bird in the hand—
Basic physics says current (I) = voltage (V) / Resistance ®.
Up V or reduce R and current goes up.
With 5 cell in series, V = 5 times larger.
Now for resistance, not a simple 5 x.
Remember the meter has resistance and is part of the circuit.
I = V/(Rbat + Rmeter)
I = 5V /(5*Rbat + Rmeter)
Note that denoinator does not increase 5 times because meter resistance is fixed. Thus I would expect larger current.
Assume all R"s are 1 ohm.
Single bat I = 1.5 / (1 + 1) = .75
Two bat I = 3.0 / (2 + 1) = 1.0
This was the way it was in physics 50 years ago at Michigan Tech. Probably not changed uch.
PS Good way to burn out a good meter. You need to add series R to reduce current levels.
I would suggest that you measure the current a servo in the circuit. This may be more relevant to you issue.
I can understand that but why would nicads be different than alkalines. I changed to 2 of each to bring it into the range of my meter and now what I am seeing is 1 alk=5 amps and 2 alk(series)=7 amps
1 nicd=6 amps and 2 nicd= 9 amps
OK now I think I can see. If the internal resistance of the meter has an effect then the internal resistance of the batteries would have the same effect. Nicds have lower int res so the amp reading is higher. Got it now.
All the battery chemistry’s are different. In reading about the 2008 Footy Euro GP, the top 8 finishing boats used Litium (not LiPo or Ni-Mh) batteries and it sounds like they last forever and they are not rechargable. They sound somewhat expensive.
Four 2500 ma-hr NiMh batteries can be purchased here in the States at Walmart for about $8.00 us and with good care & feeding, last a long time…
OK, I finished testing all my old Nicd’s and they are all in the recycle bin. Now I can start again. I have searched the net and I am just overloaded with info. I have pretty much decided to go with NIMH(less toxic) and individual AA cells(so I can throw out one bad cell instead of a whole pack). What I would like from you guys is reccomendations for chargers that you have found good. Brand name and model please. All the web stuff I could find is aimed at airplanes and cars and I think boats have less demand on the batteries. Basically I want to replace my AA alkaline use with AA NIMH. I think I need if possible 12v DC or 120v AC operation(for pond and home), charge and discharge and mah readout(so I know when a cell has gone west(not election related:) )). If you can think of any other things I need or should want please chime in.
Go to walmart and get the pkg with 4 Ni-Mh 2500 ma hr (recommended) and a charger with a cig liter and a 110 VAC for ~$20. Also pick up a 4 pack of 2500 ma hr batteries for ~$8.
You will be set for a number of years
I just went to all the stores in town(we don’t have Walmart) charger and 4 2500’s around $40, package of 4 cells $20-$25. So you don’t think the discharger and mah rater are worth the bother? I was a little concerned with only being able to charge 4 cells at once but I guess once you get all your spares charged that’s all you’d need. There was one Energizer charger for $75 that would charge 4 cells in 15 min. and it had a couple of functions that I have to investigate. I’ll go do that now.
I would highly recommend the DuraTrax Piranha AC/DC Peak Charger. It will charge NiCd and NiMH battery packs from 1 to 8 cells. It has programmable charging parameters (battery type, capacity, primary charge rate, trickle charge rate, peak sensitivity, etc…) with the ability to store 10 different charging profiles. The minimum fast charge rate is 100mAh. The maximum charge rate is 3000 mAh when used with an A/C power source & 5000mAh with a D/C power source. After the completion of the charge cycle the unit will display charge statistics (total mAh inputted to the battery, total charge time, peak voltage, etc… This particular unit does not have a discharge/cycle option. Since NiCd batteries are rapidly becoming obsolete and NiMH batteries don’t need to be cycled to maintain battery health, the absence of a discharge/cycle option is no big loss. If it all seems overly complicated just to charge a battery, the unit also has an AUTO setting that monitors the battery pack during the charge routine & automatically adjusts the charge current to an appropriate level. My dog could almost use this thing (a monkey could for sure). It was retailing for $49 USD but like everything else it’s been bumped up to $55 USD. I felt it was a screaming deal. It’s nice to know that you’re not cooking your battery packs to death with a crummy “plug it in & let it go all night”, “hope for the best”, trickle charger. If money were no object, one MacDaddy of a charger would be the Hobbico Accu-Cycle Elite charger. It’ll do NiCds, NiMHs, Li-ion & Li-po batteries. The charger & a compatible Li-po balancer is going to set you back around $200 USD. Ouch!! I don’t run lithium-based batteries in anything (something about the possibility of spectacular fires leads me to caution), so the DuraTrax unit does my cooking proud.
Happy Yachting - Kip
The Tower Hobbies substitution looks like the same charger for $5 less. I would have to make a tray to use individual cells. This brings up a point. Since this charger only has two leads it obviously charges the batteries in series and if you had a bad cell it would be one of eight. The factory chargers (duracell,eveready etc) say they give individual info on up to four cells (although not as much info). That might be helpful for weeding out weak cells. Not a criticism, just a thought. I read a lot of complaints that the Duracell 15 min charger wouldn’t charge other brands. Anyone add to that? Anyway thanks for the info Kip, it sounds like a decent charger and at the moment goes to the top of the list.
After reading a thread about top 8 boats at EURO GP using Lithium, I did some google research and found out that there are a lot of different Li battery chemistries.
Straight Lithium Energizer ($11/4 cells at Rite-Aid drug stores- $20/8) are not rechargable, but 4 cells weigh about 0.6 oz less than 4 Ni-Mh and pack a lot of energy. They say you can rece for weeks.
Li-Po’s are rechargeable and are famous for 4th of July efx. Need to use caution and buy a charger designed for them.
I thought Walmart was eveywhere. To bad.
Theres one 30 miles to the south and with gas at $1.37 a liter(around$4 a Am. gal) it cost a lot to look. I’ll look next time I go there. They are building one here
Disposable Lithium Energizer AA batteries weigh 14.5 grams each. A 4 pack is a svelte 58 grams. Add to this a certain amount of weight in some manner of contraption to actually form these individual cells into a usable battery pack (battery box, leads, etc…). Lets say you’re fairly crafty & you can weasel it down to 60 grams total. That’s a heaping load lighter than my Ni-MH 4 cell AA pack that tips the scales at a whopping 115 grams. The only real practical advantage to Lithium Energizer batteries is the weight savings and a very long shelf life. It’s a substantial weight savings (one tenth + or - of the boat’s total mass) and if your goal is to travel to exotic locales to win International Footy Regattas and dates with French fashion models, you’d be silly not to use them. At $20 USD for an 8-pack they seem pretty inexpensive. At least until you actually compare them to something else. Lithium Energizer AA batteries are rated at 1.5 volts and 3000 mAh per cell. So, a 4-cell AA pack will deliver 3000 mAh total at 6.0 volts (18 watt/hours) over the life of the battery for a cost of $10 USD (1.8 watt/hours per dollar). Compare this to a $20 USD 4-cell AA Ni-MH pack rated at 4.8 volts and 2000 mAh and the price difference really jumps right out. The Ni-MH pack is only going to deliver 9.6 watt/hours, just a little bit over half of the power available in a Lithium Energizer pack. Sounds bad for the Ni-MH battery until you take into account that it can be recharged hundreds & hundreds of times. After 250 cycles it will have delivered a staggering 2400 watt/hours for a total cost of $20 USD (120 watt/hours per dollar). That makes a Ni-MH battery 66 times cheaper than disposable Lithium Energizer batteries!! Neither battery chemistry is probably ever going to really deliver 100% of it’s rated capacity it just makes for easier math. Some people might make a big deal about the lithium cells having more capacity than the Ni-MH cells (3000 mAh vs 2000 mAh). In reality that’s a fairly minor issue. If you sail a Footy long enough in one session to completely drain a 2000 mAh battery, you’ll probably need to get skin grafts on your thumbs. If you think that running a 6.0 volt pack vs a 4.8 volt pack is of any real advantage you’re probably just dreaming. Decreasing the total transit time of your servos by a few hundredths of a second is unlikely to produce any noticeable improvement in your boat. Increasing the maximum output torque of your servos by using 6.0 volts isn’t always the best thing either. Sure, it will put out more torque, but you’re also wearing out the servo’s motor much faster. If you’re indeed overpowering your servos on 4.8 volts, running 6.0 volts really isn’t the answer – a bigger, more powerful servo is. For those that are undeterable in their desire for a 6.0 volt pack bear in mind that a BEC style of receiver will generally regulate the 6.0 volt input down to 5.0 volts to drive the Rx board & servos. If you really want 6.0 volts, you can generally bypass the BEC circuit & input the battery power to the receiver via one of the servo output sockets on the Rx (“Y” the battery pack & a servo together & plug them into the proper servo output socket on the Rx). It’ll get you 6.0 volts, but why bother?? Here’s my own personal strategy: For casual, just mucking about sailing, I use a 56 gram 4.8 volt 750 mAh Ni-MH AAA battery pack (yes, those forbidden AAAs). If I were to actually sail in a sanctioned race (which I’m far too lazy to ever do), I would install a Lithium Energizer AA pack for the significant weight savings (and to satisfy the silly rule). The boat itself would trim out very close to the AAA Ni-MH configuration. The Lithium Energizer batteries would be reserved for proper Regattas only & the Ni-MH batteries used for everyday casual mucking. It’s not so much the cost of Lithium Energizers that has me against them (I’ve spent more on bad cheeseburgers); it’s the “disposable” part. I’m just not real fond of the thought of my grandchildren having to filter their ground water through all the toxic stuff I’ve thrown into a landfill. The Earth did endow sailors with 70% of her surface as our domain, I feel it’s only common courtesy to try & screw it up as little as possible.
Happy yachting - Kip
I didn’t even bother to read your response to Don’s original mail regards batteries. In one simple paragraph - please tell those of us who don’t have hours to spare what the hell you are trying to say.
Sorry, for my extended ramblings. Here’s the abridged version: Disposable Lithium cells are hard on the environment, expensive compared to rechargeable cells and offer no performance gain except reduced weight.
Happy Yachting - Kip
Radio Shack is also a source for AA NiMH. My local grocery chain also sells a charger/cell combo. They’re 2200 mah cells - I forget the brand.
My personal recommendation for a charger, being a cheapskate, is the Hobbico multi-charger from Tower at about $30 US. You’ll have to make leads from banana plugs.
It’s a constant-current charger with 4 outputs, each with manually-selectable output. I tend to be pretty aware of what I’ve got going on, but it IS possible to cook a pack with the 500 ma setting (but that’s the omigod-the-regatta-is-this-morning setting). Get some multi-cell battery holders from Radio Shack, mat up some connectors and you’re in like Flynn…
I am still having issues with the conversion from NiCads to NiMH batteries and knowing when they will quit. :mad:
I can’t count any more, the number of time “blue” language has spewed forth when my digital camera craps “SUDDENLY” and without warning.
When I used the good - but old - NiCads, I could see a decline in storage times as the batteries lost their charge. Pull the old ones, reinstall the fresh ones and continue shooting. The NiMH on the other hand present me with a series of photos and after taking one, the next has no battery life what-so-ever! They don’t even give my battery meter on the camera time to display the low energy amount left! :mad:
So now, I’m supposed to take these same pieces of crap, and “hope” my boat will be able to be steered back to shore??? You have to be kidding me - that after camera issues I would trust a model boat to these “wonders” of modern electrtical energy. Naw - sorry, but I’ll continue to purchase (getting more difficult) the AA NiCads on-line and feel more comfortable in how they respond to me as their life is expended.
NiMH that I am using are 2500 MaH so it’s not like I’m trying to get by on a 700 MaH battery either.
Seriously, no one has still been able to explain why the sudden drop off in camera use between individual photos - and even here at work, NiMH are last resort batteries. Most of our Sheriff vehicles use Alkaline batteries in their squad car digital cameras - just because they hold a charge and don’t die suddenly in the middle of an accident investigation photo shoot. Also, easy for officer to run into any drug or convenience store to grab more alkalines that are fresh and ready to be used immediately - no need to pre-charge.
If any of you guys that are, what I would term, “Battery Wizards” I’d sure like to hear your thoughts on why I exerience the sudden and unexpected drop off rates in the NiMH that I’ve tried. Unless it’s a small closed pond, I still will swear by (not at) my NiCads which seem more reliable and easier to judge operating times.