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[Garabaldy]

something i have been thinking about recently.  When they run out of power will the motors stop dead or will there be a noticable difference in available power to the motors there by acting like a warning that the batterie is flat and the boat needs to be taken a shore?  I have still never had a full run with any of my boats but as i sail on a huge loch i want to make sure i dont have to get wet!

[Martin (Admin)]

I think SLA (Sealed Lead Acid Battery) have the slowest 'run down'  of most battery types, plenty of return to shore power. 

[Colin Bishop]

That's true, but if the model is showing signs of slowing down it means that the battery is in a lower state than it ought to be and should be recharged as soon as possible. Generally speaking, lead acid batteries should not be drained lower than 50% of their nominal capacity so that if you have a 6 amp hour battery it should be treated as if it is a 3 amp hour one for practical purposes. This is very different to the NiMH types which will deliver full power almost until they are flat.

It's always best to try and estimate your average current draw when sailing so that you can get some idea of how long the boat should be sailed for before changing or recharging the battery. The reason people use SLAs is that they are relatively cheap and convenient and can act as ballast. In a scale boat you can usually put in enough battery capacity to give plenty of sailing time without having to worry much about the 50% rule.

Another little quirk of lead acids is that if they do run flat in the middle of the pond, set the throttle to stop for a few minutes and then apply it again gently. The battery will probably have recovered a little in the meantime, maybe enough to get you back to the bank but it won't have done it much good!

Colin

[Garabaldy]

typically how many times could you totally drain a lead acid before it dies?

G

[Colin Bishop]

Only once in most cases - unless you are very lucky. SLAs don't like being emptied.

Colin

[packy46]

Hello:
Can I have a follow up question please....
An SLA with a rating of 12 v/7ah , using 2x motors , at 3 amps each max , should run approx 1.1 hrs , at full speed,probably won't do
full speed for an hour- anyway , if thats right , Bob's my uncle....
Now I see on the battery picture on line , initial current / and cycle current,(2.7 / 3.6 max.)does this mean recharge rate?.
Now I don't even know who my parents are....
Need help
Thanks
Tim

[Ghost in the shell]

I took a 6v down to 2v, and that was it, dead jim!!

[wombat]

I suspect that by the time you notice a loss of power with a SLA you are getting into the realm of reduced battery life. The load you are applying determines how low you can run the battery. The higher the load the deeper you can discharge.

Remember also that the nominal AH (amp-hour)rating of the battery is based on the 20hr rating (i.e the AH rating measured for a discharge time of 20 hours) - this is a current of 350mA. The AH for a 1 hour discharge - for a Yuasa NP7-12(7AH nominal 20hr rating) the AH rating for 1 hour discharge is 4.2AH - so for your two three amp motors, the run time before dangerous discharge of the battery is of the order of 40 minutes.

Not sure what you mean when you say:

Now I see on the battery picture on line , initial current / and cycle current,(2.7 / 3.6 max.)does this mean recharge rate?.

Can you point me at the picture on line - so I can understand a bit better and maybe give you a meaningful answer because I cannot relate these figures to the data I have

Tim