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Old Jun 29, 2007, 07:12 AM
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Millbrook, Alabama
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Mini-HowTo
Battery Basics

I can't find anything in the boat forum about battery basics. The beginner can be confused with all the choices and maintenance procedures. There is an overwhelming amount of information on the aircraft forums, but most of it doesn’t seem to apply here because of the specialized battery types used in aircraft. We need our own specialized section or thread so…

…I ‘m starting this thread in hopes that knowledge will flow.

Captain Slick

"Weevils...the breakfast of iron men sailing wooden ships!"
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Old Jun 29, 2007, 07:13 AM
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Millbrook, Alabama
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I purchased my first set of NiMH (Venom 2400s) batteries and charger and have some questions. The battery package says to charge @0.5amp for extended life or 1amp for improved performance. It also says “DO NOT TRICKLE CHARGE BATTERIES”. I charged @ the .5amp rate and they were charged in a couple of hours. I’m not used to that! My NiCad’s charge very slow @ 12-24hrs.


1.) These get very warm…is that normal and are they supposed to be “quick charged”?

2.) Can I use my radio wall chargers to charge these batteries? I think they charge at a very slow and low rate.

Thanks

Captain Slick
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Old Jun 29, 2007, 08:28 AM
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Euclid, Ohio, United States
Joined Sep 2004
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Batteries fall into one of four major groups, based on chemistry: lead acid gel cells; nickel cadmium (NiCd); nickel meytal hydride (NiMh); and lithium polymer (lipo). Each type has some advantages and disadvantages when it comes to charge rate, discharge rate, storage capacity, and voltage.

Lead acid are old school technology. They are generally 6 or 12 volt, with various Amp hour capacities available. They are a good choice for big displacement hulls like tugs and freighters - something you want to run for a long time. They are trickle charged for about 12 hours.

NiCd and NiMh are similar in voltage and AHr ratings. Each cell has 1.2 Volts, with a capacity of 600-1700 MAH (NiCd) or 1800-4000 (NiMh). Both can be trickle or quick charged. I trickle charge them at aboput .10 Amp charge rate for about 12 hours before going to the lake. At the lake I quick charge 7.2V (6 cell) packs at a 3 Amp rate; this gives a charge time of about 1.5 minutes for 100 MAh (1500 pack is charged in about 20 minutes). They do get warm while quick charging. After running them in a model, allow them to cool off for about 15 minutes before charging. I have an AC/DC Peak Detection charger which allows me to charge off house current or from a 12V car battery.

Li-po bateries are usually used in some of the fast electric speed boats. They have a larger capacity for a specific voltage than NiCd or NiMh. Their disadvantage is that they can't be fast charged (yet). You generally charge these at less than 1 Amp charge rate, which means charge times of an hour or more. Because of the battery chemistry, a 2 cell li-po is 7.4 Volts. You NEVER EVER want to run these cells below a certain voltage. Over discharged cells will plump like and overcooked sausage, and can possibly catch fire.

Related to batteries are the connectors used on the battery packs. Gel cells have tabs, use spade connectors on the ESC battery leads. NiCd and NiMh usually come with the "standard" Tamiya molex plug. The standard plug is okay for most applications, but has a high resistance of about 1.5 Ohms. Deans Ultra plugs are better, with a resistance of about 0.4 Ohms, (equivilat to 8" of wire). You can convert the stanard Tamiya plugs to Deans Ultra Plugs in about 10 minute per battery connection. Yopu can also buy NiCd and NiMh batteries with Deans plugs already installed. Lipo batteries have several connectors as standard right now - some use the Deans Ultra Plug, some use the JST plug and other have some version of the standard Tamiya molex plug. Lipos also have a separate charge plug on them.
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Old Jun 29, 2007, 08:32 AM
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Brooks's Avatar
Bozeman, Montana, United States
Joined Aug 2003
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Rather than starting a boat battery thread, how about looking at the other RCGroups forums, eg: Batteries and Chargers:
http://www.rcgroups.com/batteries-and-chargers-129/

Or go to a vendor like Radical RC. Dave has a lot of battery information:
http://radicalrc.secure-mall.com/shop/

I found this site comprehensive and helpful:
http://www.batteryuniversity.com/index.htm
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Old Jun 29, 2007, 08:40 AM
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I love my NiMHs, have tossed all NiCds (responsibly recycled, actually).
One of the points I've heard on charging NiMH is that slow/trickle charge should be AVOIDED (and see the Battery University for more on this). It's not bad in itself, but NiMH apparently doesn't take well to overcharge, and the negative delta-V is hard enough to detect at high charge rates, tougher at trickle rates. So if you leave them on a trickle charge too long, I guess badness happens.

PM
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Old Jun 29, 2007, 09:47 AM
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That Rcgroup thread is way to confusing for someone that is new...to include me. Just too much stuff! The Battery University Site is great. I really like the charge chart. I am still a little confused on the preferred NiCad charge rate though. I thought a slow charge like the one that comes with the radio charger is the best for a NiCad, but the charge chart

http://www.batteryuniversity.com/partone-21.htm

says fast charge preferred over slow charge…me be a little confused on this?


Captain Slick

oh...one more thing...it says to slow charge the intial charge for both NiCad and NiMH. Is that right?
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Old Jun 29, 2007, 10:01 AM
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Motor City
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Tx chargers are trickle style because they're CHEAP, not because it's best technically. The makers also include the cheapest little battery packs they can get away with.

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Old Jun 29, 2007, 11:05 AM
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Central Missouri,USA Along the banks of the Missouri River
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Also, do not use a charger that is for Nicd's only for a NiMH.You need a peak type charger. I am embarrassed to say when I got my first NiMH batteries I thought my old Mega 1 charger was good enough.Well, I couldnt understand why I was only getting 6min from a 3300mah NiMh.After asking for some help here and doing some searching on the web, I realized what my problem was.Now I have a Vision Peak 2,and I get 20+mins runtime.I believe it is possible to damage a NiMH battery using a NiCd battery charger.My Vision Peak 2 charges both NiCd and NiMh and I have a wall trickle charger for my Sealed Lead Acid batteries.(SLA) Hope this helps a little.
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Old Jun 29, 2007, 03:03 PM
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Dave says (I hope I am quoting him correctly) that the delta peak detection system used by the fancy chargers depends on all cells in the battery pack being similarly full or empty of juice. A brand new battery pack's cells will not meet this criteria, so a slow trickle charge is necessary to bring all cells up to the same level. After you have trickled & then discharged (in your boat, plane, Tx, whatever) a couple times, the cells should be equalized enough so that the fancy charger's delta peak detection system can work properly. After that, a moderately fast charge (1-4C for NiCd,0.5-2C for NiMH) will be better for your battery than repeated trickle charges. I just stick with 1C for both types to save myself some brain confusion :-).

The definition of trickle charge varies among battery mavens, but I will define it as 0.1C, the commonly found output of the plug-in-the-wall-bricks supplied with radio gear. e.g. to trickle charge a 1000mah battery, use a 100mah rate; to fast charge it with a delta peak fancy charger, use 1000mah=1amphr rate. The charge time will be 1.4x the charge needed, so for this simple example, it would take 14 hours to recharge a dead battery at trickle rate and 1.4 hours to recharge at fast charge rate. Dave has the complete equation, taking into account charge rates other than my simple math example, for those interested.

One problem with trickle chargers is that they are dumb....they don't know when to quit. It is very easy to overcharge your batteries with trickle chargers because you don't know exactly how much juice you used yesterday at the pond, so you don't know exactly how long to let the trickle charger run. NiCds are relatively immune to overcharge (I preferr to only overcharge NiCd's via trickle for a few hours, say overnight, but not all week)....but NiMHs are not immune. Once NiMHs are full, they get hot pretty quickly (a matter of minutes), and heat is bad for any battery.

Also, NiMH have a limited number of recharges in them, around 300. If you use only a little charge out of the NiMH, then recharge it, you are not going to get the lifetime current flow out of the battery. For example, if the pond used up 40% of the juice, you could get 2 pond trips per charge, 600 trips total, before the battery is worn out. If you recharge that 40% after each trip, you will only get 300 trips to the pond. Since they don't leak away charge while sitting on the shelf to the same extent as NiCds, I don't recharge my NiMHs until the model shows signs of needing more juice. Of course it depends on the model and the circumstances - an airplane running low on juice is in more danger than a pond boat, usually.

NiCds can be long lived; I am using NiCd's in my vacutug that are left over from my RC helicopter days of 14 years ago. They only hold about 1/2 the original capacity, but that's enough for an hour's run or more with the tug. And since they are already paid for, they provide cheap thrills. Using old NiCds requires formating them with a trickle charger just as if they had been bought new yesterday.
----------------
I understand the confusion problem, been there myself. Batteries for models, particularly electric planes, are state of the art. The knowledge to use them is not hard, but it does require more intellectual effort than just using disposable alkalines (which still have their place in my model ops, namely the Rx battery pack for seldom used models).
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Last edited by Brooks; Jun 29, 2007 at 03:25 PM.
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Old Jun 29, 2007, 05:24 PM
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well when it comes to charging, its usual for me to give most batteries a 12 to 16 hour charge, though the 70ma charger for the tx usually means a 24 hour charge, until the 8 cell reads 11.5 in the display.

as for seldom used models, get a BEC speed controller and do away with the battery pack! let the esc do the job!
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