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 Low power indicator

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vigo
Midshipman
Midshipman



Posts : 72
Join date : 2021-02-11
Age : 60
Location : Derbyshire UK

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PostSubject: Low power indicator   Low power indicator EmptyMon Aug 15, 2022 7:34 am

Although I've been unsuccessful in sailing any of my recent creations (mainly due to a lack of local sailing venues) I'm still haunted by something that happened over 40 years ago when my boat 'ran out of juice' in the middle of a canal marina. You can imagine the rest.

Question.
Is there a reliable tool/method/whatever out there somewhere that will tell me if the boat is about to die? eg a flashing LED on a mast or something. Something that will give me enough time/power to recover the boat without resorting to getting wet.

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Martin555
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Martin555


Posts : 334
Join date : 2021-08-07
Age : 64
Location : Southampton. U.K

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PostSubject: Re: Low power indicator   Low power indicator EmptyMon Aug 15, 2022 8:15 am

Hi Vigo,
I have just had a quick look around and found this.

https://www.modellingelectronics.co.uk/products/low-battery-indicator-model-boats/

I think there are different alarms available for the different battery types but hopefully this might guide you in the right direction or at least give you a starting point.

Martin555.
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vigo
Midshipman
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Posts : 72
Join date : 2021-02-11
Age : 60
Location : Derbyshire UK

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PostSubject: Re: Low power indicator   Low power indicator EmptyMon Aug 15, 2022 10:15 am

That seems to be the perfect solution... and cheap too (that's what I like).

Ordered. Cheers.

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Martin555
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Martin555


Posts : 334
Join date : 2021-08-07
Age : 64
Location : Southampton. U.K

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PostSubject: Re: Low power indicator   Low power indicator EmptyMon Aug 15, 2022 10:53 am

Hi Vigo,

Great.
Let us all know how you get on with it.

Martin555.
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barriew
Captain (moderator)
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Posts : 2543
Join date : 2011-11-26
Age : 81
Location : Thaxted, Essex

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PostSubject: Re: Low power indicator   Low power indicator EmptyMon Aug 15, 2022 11:21 am

Vigo

I know of three sites in Derbyshire for model boats - Derby, Buxton and the outskirts of Burton on Trent. As far as I know they all have active model boat clubs.

Barrie

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Roadrunner
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Join date : 2011-06-10
Location : Aberdare South Wales

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PostSubject: Re: Low power indicator   Low power indicator EmptyTue Aug 23, 2022 11:23 am

You have to watch on power indicators they detect the amps rather than the voltage, even a “dead battery” can still give you a full volts reading, this is more obvious in the new lithium technology battery’s than the older nicad cells. Nickle hydride battery’s should just be outright avoided when modelling as they are for lower use devices like your tv remote. They simply do not have the stamina for any long usage.

Now all that said a lot of modern rc electronics have some warning systems built in, especially speed controllers pretty much most of them now actually give you a warning on low power by cutting out the power for a moment as a visual indicator, for Rc cars this is easily noticed on boats, it comes down to learning the boats quirks before you can spot that blip moment. Aircraft are Ona whole other plane literally as you tend to do timed flights knowing your Battery’s flight time and when to bring it back.

After almost 2 decades of boating battery’s is something we have nailed down to almost an art to not loose power mid sail, and that’s all to do with your math!  Without going into a long post that would take hours to read simply look at your amp-hours usage for each item that’s draining power and divide it by the amps your supplying as your power (ignore volts) that will give you a total amp hour usage which is pretty easy to work out into minutes. 
Eg…
12v motor using 10amps and a 12v 3.4 amp hour battey will give you about 3.4 hours of run time! Ok in theory that looks right but it’s a variable Because that’s a non “loaded” motor just spinning with no friction or force applied, here’s the kicker… half it! Now you have 90 mins and that is about as accurate as it’s going to get on a motor, it’s all variable subjects to your speed or throttling on and off but that is calculated at full speed all the time and honestly 90 mins for something like that is more than enough! ( damn I would get bored)

Servos are a nightmare… calculating for sail boats on servos alone is far from accurate, but there are key warning signs… low power can be seen but you again need to know your boat at a fresh start and how it handles wind speeds while u have fresh battery’s, after that any indication of low power can be spotted because the boat no longer responds or handles the same as a fresh set.

Rule of thumbs … is using lithium battery’s don’t worry they have auto stops and you will see that warning easily without a gadget atttached

If using nicads (7.2) packs with a standard 540/600 motor and servo setup the. You get about 20 mins of run time on a 3200 amp hour pack , (3200 being The more common) 5000 are preferable but then you might as well do lithium’s becuaee they are so much cheaper now!

Lead acids easy Maths I demoed above that’s that’s pretty much fool proof.

1.5v battery’s for everything else you just pray to Thor that he charged ya shit up properly

 // oh side note// 

Rechargable aa/aaa 1.5 v batterys are not true 1.5v fully charged they are 1.2v.. keep that in mind as a freshly charge set will always be a lower run time and voltage output than whacking some duracells in there.

RR

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