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Author Topic: batteries !!!!  (Read 3809 times)

tugboattam

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batteries !!!!
« on: May 25, 2014, 12:47:00 pm »

Hi all,  Im not very clued up when it comes to batteries so my question is would a 9.6V 4300mAh NiMH COMPACT rechargeable battery pack give me about the same run tim as a 6v 4mah lead acid battery ?  All my boats are slow running and have lead acid batteries but the part built fishing boat I have bought does not have the room for one of these.  Thanks in advance for all replies.
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Hellboy Paul

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Re: batteries !!!!
« Reply #1 on: May 25, 2014, 01:05:53 pm »

Slightly longer run time with the 4.3ah NiMH but with the major advantage of being able to quick charge them in about 30 minutes lakeside with the right charger.


Paul..
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boatmadman

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Re: batteries !!!!
« Reply #2 on: May 25, 2014, 05:16:19 pm »

Provided your motor can take the higher voltage, no problem. The boat will run faster at full throttle or last longer on reduced throttle.


You could contact component shop and ask them to make up a 6v nimh pack for you?


Ian
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tugboattam

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Re: batteries !!!!
« Reply #3 on: May 26, 2014, 11:08:45 am »

Thanks for both your replies they help. do either of you know anything about these LiPo batteries ? cos these things go way over my head, could I get better results with one of these ?  Again thanks in advance for any replies.
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Hellboy Paul

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Re: batteries !!!!
« Reply #4 on: May 26, 2014, 11:29:27 am »

LiPos have a much higher discharge rate than NiMH but require a special charger & cell balancer they are more suited to fast electrics etc where weight is a premium.. NiMH batteries are a bit more forgiving when charging although I must point out that ANY battery is dangerous if it is misused or abused...


Personally, for slow models I would stick with NiMH.


Paul.
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inertia

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Re: batteries !!!!
« Reply #5 on: May 26, 2014, 11:53:38 am »

The discharge rate is dictated by the load and not the battery, but I'd agree with Paul ref using NiMH battery packs in the circumstances. If you don't really need the light weight or very high discharge rates of LiPO's then best avoid them.
DM
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essex2visuvesi

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Re: batteries !!!!
« Reply #6 on: May 26, 2014, 04:22:36 pm »

other advantages of reduced weight include:-
  increased run time
  lower current draw
  less stress on drive components


It's really just a balancing act of cost/benefit
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Jon

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Re: batteries !!!!
« Reply #7 on: June 01, 2014, 08:34:30 am »

Hi all,  I'm not very clued up when it comes to batteries so my question is would a 9.6V 4300mAh NiMH COMPACT rechargeable battery pack give me about the same run time as a 6v 4mAh lead acid battery ?  All my boats are slow running and have lead acid batteries but the part built fishing boat I have bought does not have the room for one of these.  Thanks in advance for all replies.

Just a further note about lead acid batteries, it is generally advised that the capacity should never be taken below 50% so your 6V 4Ah battery is really a 2Ah battery to 10V discharge. The NiMh can be discharged right down with little concern, so you can take that as full capacity 4.3Ah.
When you look in wattage terms the lead acid (SLA) battery is 12Wh (6V x 2Ah), and the NiMh is 41Wh (9.6 x 4.3Ah).

So as you can see the Watt Hour rating (the usable power capacity) of the NiMh is much higher than the SLA, combine that with the lighter weight, and better recharge times the NiMh is overall a better choice when you don't need the free ballast.

Assuming you are running electronic speed controls, the power loss when throttling back the 9.6V system to the same rpm as the 6V system should be very little.
So as has been mentioned the 9.6V system will give you better top speed, more gradual throttle response (usually. This is due due to higher voltage pulses to get the motor rotating from still better) and a longer runtime to boot.

Rgds
Jon
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roycv

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Re: batteries !!!!
« Reply #8 on: June 01, 2014, 10:00:39 am »

Hi tugboattam, there is a difference in the measurement of amp hour capacity between Lead acid and Nicads / Nimh batteries.
The Nimh cells are rated for their capacity at the 5 hour (discharge) rate but lead acid batteries are rated at the 20 hour rate.

For a 4 amp hour lead acid battery, then 4 amp hours divided by 20 = 0.2 (amps) will give the full capacity of the battery for 20 hours.  If the current discharge rate is higher then the efficiency of the battery goes down and there is less current available.  Typically some of the power in the battery comes out as heat, so warming up the battery.

For the same rated Nimh battery then 4 (Ah) divided by 5 (hourly rate) = 0.8 (amps, or 800 mamps) discharge for 5 hours will give the full discharge of the battery as per rated capacity.
Any discharge current higher than this (which we all do) will decrease the efficiency of the battery, heat etc.
So as has been pointed out previously the lead acid battery will last a lot less than the Nimh battery depending on discharge rate in amps.
C is often used as a reference to capacity of the battery.  The charging rate is usually recommended as c divided by 10 ( so if C = 4 amp hours then the charging rate is 0.4 amps, for 14 hours).  The extra 4 hours is that the losses in the charging are taken into account by an extra 40% charging.
Also you may see a recommended maximum discharge rate of 10C for the 4 amp hour battery this 10 x 4 =40 amps.  Only if it says so!!

Lead acid batteries have a recommended charger and these do not apply a constant current ,but a constant voltage, with some current limitation.  This is called taper charging as the the charge rate (current) tapers off until fully charge is reached.  The voltage on the battery rises as the charge goes on until it nearly matches the charging voltage.

Nimh cells have constant current charging.

I personally break all of the above rules but if you break the rules it best to know which ones they are!

I agree with previous contributor and throttling back is best bet, but a bit of extra power for stopping is most welcome.

My (defunct) L/Acid batteries are mainly used to hold down things being glued and this is where weight is good! 

Hope this helps,
regards Roy

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malcolmfrary

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Re: batteries !!!!
« Reply #9 on: June 02, 2014, 10:44:49 am »

What size and shape is this compact pack?  It would probably be easier to use 5 cells and wire them in a string so that they could be placed where you want them to go rather than where a solid lump demands to go.  5 cells because that keeps you on the 6 volts that you are used to.  If 4300mAH cells are used, you still get a longer run time than you would with 4000mAH as well, even if it is only 5 minutes on the hour.
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Peter Fitness

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Re: batteries !!!!
« Reply #10 on: June 02, 2014, 11:01:51 pm »

I use SLA batteries exclusively in my models, as much for ballast as their being a power source. I always charge them at the end of each sailing session, and store them fully charged. However, I have been known to run them down to the point where the model stops mid-lake, but what percentage of their capacity that constitutes I have no idea.


One advantage of SLAs is their ability to recover some power if left for a few minutes, this ability has allowed me to bring the model back to shore. I know that it has been frequently said that it is inadvisable to run down SLAs beyond 50% of their capacity as this will shorten their life. Given that some of my SLAs are almost 10 years old, even though they have often been run flat, what life could I reasonably expect from them?


Peter.
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nick_75au

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Re: batteries !!!!
« Reply #11 on: June 03, 2014, 04:21:28 am »

Deep discharging does shorten the number of cycles, though if they are 10 Yo you're doing something right :-))


Biggest problem for me and SLAs is the fact that I don't get out and use them, I have a good number of them that are no good anymore, Lipos if recharged to a storage charge keep their voltage for many many months with no attention.
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tugboattam

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Re: batteries !!!!
« Reply #12 on: June 05, 2014, 10:42:34 am »

Thanks to everyone for your replies, most helpful.
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