Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Batteries & Chargers => Topic started by: guitar man on August 16, 2011, 05:38:23 PM

Title: 6volt lead acid battery
Post by: guitar man on August 16, 2011, 05:38:23 PM
Hi all 

Have been out sailing my pride and joy and thought that its top speed was dropping off , took a guess that the battery was beginning to loose charge so went home. However when I put a meter on the battery it reads 5.8 volts which does not seem too low (or is it) the battery is 6volt 4.5 amp if I put it on charge it does not seem to get above this unless I am not doing it long enough but the charger I have does not seem to have a cut off or at least I am not sure of it ,and don't want to over charge it. Any thoughts. As always thanks in advance for any comments.

Regards Tony
Title: Re: 6volt lead acid battery
Post by: Pirate on August 16, 2011, 05:52:47 PM
Hi Tony,
   not wanting to insult your knowledge but it is not the voltage in particular that matters. It depends on your charger; if your charger can charge at 500 ma it will put this into your battery every hour thus 4.5 amp battery charged theoretically in 9 hours, regardless of if it is a 7.5 v, 6v, 12v battery etc. The faster/ higher the input IE 500ma / 1 amp / 2.5amp the shorter the time, in general if you charge at 500ma over a 12 hr period most often this will charge a flat ish battery to full. The voltage of a 6v battery may register as much as 8v when charged but this top voltage will quickly diminish to a nominal 6v within a few minutes of running. So check your chargers output, divide that into 4.5 amp and you will get an approximation of how many hours to charge.
   The other consideration is if your boats prop size/ motor size is large and draws a high amperage, a lead acid or gel cell will deteriorate faster than say a NMH or NICAD dry cell. Thus if your set up eats the amps then perhaps if after a full charge as per above advice the battery still does not come up to your desires then concider a replacement.

Trust this helps
Title: Re: 6volt lead acid battery
Post by: petermun on August 16, 2011, 05:53:46 PM
When the battery is put under load, eg, running the motor, the voltage will probably drop another volt, therefore only about 4.8 volts being applied.   Sounds like the battery is reaching the end of its life. but how old is it, and can you try with another battery?  Pete
Title: Re: 6volt lead acid battery
Post by: guitar man on August 16, 2011, 07:42:19 PM
Thankyou both for your reply

Pirate you can not insult my knowledge, as in this matter I have none  {-) {-) the charger that I have is marked up 6/12 volt 300 ma 3.6va(max) will this do the job?.Does this mean that I will need to charge the battery for 15 hours ?How do I tell in the future that the battery needs say a full charge , a half charge etc or can you not.

Petermun .
     The battery was new though I am aware that it could still be self life at this moment in time I don't have a second battery not 6 volts anyway but must get one cheers  O0

     Regards Tony
Title: Re: 6volt lead acid battery
Post by: Pirate on August 16, 2011, 09:57:54 PM
Hi Tony,
     from your description, yes 15 hours seems right. You can hear at very close range the battery 'fizz' and will be slightly warm when charged/over charged. I say this not as a guide more as a mental warning as this is not good for the battery but will allow you to know when this state of charge has been met
     As regards charging 1/2 full etc and when to charge. This is somewhat a mine field and one that only you can through experience determine. If you have a meter then you could measure the amperage draw of your motor/prop set up. Though this will be only a guide it will help thus; if you find that your boat in the bath on half throttle draws 4.5 amps then you can guess that the battery being the same 4.5 amps will give you a run time of 1 hour. If the draw is 2.25 amps then you will get 2 hours. So if you are out at the pond and run for approx 1 hour and you know the rough draw of your boat then you can hazard a mathematical guess of the amperage used ( amps = duration and volts = speed ) thus ; Boat draws 2.25 amps, run time 1 hour = 1 hour remaining in battery or 2.25 amps left which ever way you wish to see it. Then upon returning home you can adjust the charge time. This is a very loose way to govern it but it does help.

Kind regards
Title: Re: 6volt lead acid battery
Post by: guitar man on August 16, 2011, 10:11:24 PM
Cheers pirate very helpful,now a little more educated.I appreciate your time

Regards Tony O0 :-))
Title: Re: 6volt lead acid battery
Post by: Peter Fitness on August 17, 2011, 12:48:12 AM
My knowledge of electrical matters could be written on a pin head with a broad tipped pen, but I have had a bit of experience with 6v sealed lead acid (SLA) batteries in model boats. I have two SLA chargers, one charges at a rate of 600mah, the other at 500mah, and both have a peak detection facility, so they cut out when full charge is reached. One thing that was made very clear to me was to always store batteries fully charged, so whenever I come home from a sailing session I immediately put the batteries I have used that day on charge, and leave them charging until the indicator light flashes.

My oldest battery was bought in 2003 and is still performing well, so I must be doing something right :-)

Title: Re: 6volt lead acid battery
Post by: Netleyned on August 17, 2011, 06:54:12 AM
A 4.5 amp/hr battery will be hard pushed to give much more than half an hours run time at a current draw of 4.5 amps
Gell cells should not be run flat. Recharge after half discharge to ensure a long life.

Title: Re: 6volt lead acid battery
Post by: John E on August 17, 2011, 10:15:31 AM
Could I please add that lead acid batteries MUST be stored fully charged or they suphate and lose capacity, but other types of battery including old NiCd, NiMh and Lithium types MUST be stored part charged - or they lose capacity - been there.....

Unfortunately I have no experience with sealed lead acid as supplied for model boats (but I teach sealed lead acid for motor vehicles!), so don't charge faster than the 1C (1 hour) rate of 4,5A for a 4,5Ah battery (and I wouldn't plan to discharge faster than that either).  The 10hr charge rate generally preferred for lead acid would be 0,45A (0,5 amp) for a 4,5Ah battery - yes, I agree, keep it on charge for 12 hours at the 10 hour rate.  Just recalculate for different charge rates or battery capacities.

A lead acid cell should read 2,1V when allowed to settle after a full charge, so the 6V battery should be showing 6,3V after a full charge. 5,8V is very close to fully discharged.  I wonder if the charger is working, or if there is a break in or high resistance in one of the cables? or if the battery is simply past it's prime?


Title: Re: 6volt lead acid battery
Post by: More Coffee on August 17, 2011, 01:21:09 PM
for what its worth..

Initially i ran my batteries a little to low ..and then charge them to high low ..

Any way resurrect the batteries i bought myself a little 6/12V ... 2/4/6A battery charger..with circuitry to both desulfate and charge gel cells..

Ive read from variuos sources that If a lead acid battery is left to run below its dead should be cycled with a desulfator then charged..