Fight the Power.. ok not so cool “Calculate the power”

[Pandoramark1]

Evening All,

So after converting my old NAV light on my Pandora, to my special Home Made LED beauties total cost 90p a light , I found myself thinking I wonder what benefit I would get in terms of battery usage saving. So I tried some maths and came up with the following mess, like all good people I have shown my workings...

I have a 110Ah deep cycle battery.

After taking all electrical devices into consideration, Lights (NAV's and LED interior) clipper depth and a small compass light I am drawing 0.2A.

So if I have done this right I have worked out that my 110Ah battery will last for 6hrs based on a 90% depth of discharge and a 16.5A continuous draw

110Ah X 90% = 99Ah @ (6-hr rate)
99Ah / (6-hr rate) = 16.5 Amps

With a bit of luck at this point you are A) Still with me and B) I have not got it wrong so far.

So my question is what is the calculation that will let me find out how long it will take for me to reach a 90% Depth of Discharge based on a 0.2A continuous draw.

I hope this make sense, look forward to your responses and support

PMK1

 

[sarabande]

if you try and discharge a battery to 10% of its theoretical capacity, the lights will stop working long before it reaches anywhere near that figure.

0.2 Amp ? That's 2.4 watts from all those devices. And where does the 16.5 Amp come from ?

What are you wanting to achieve with your commendable DIY lighting regime please ? To work out how long a fully charged 110Ahr battery might last ?

 

[Playtime]

0.2A for 5 hours = 1 amp hour (Ah). So, to consume 99 amp hours (90%) will take 99 x 5 = 495 hours.

Should last all summer but you'll need a new battery for next year

It is not recommended to let your battery discharge below 50%.

 

[Pandoramark1]

What are you wanting to achieve with your commendable DIY lighting regime please ?

Trying to work out roughly how many hours I can use this before I would have to take the battery out and charge it before as you say the lights do not work, as i will not have any other means to recharge the battery (running out of funds to buy solar etc). it si just handy to know. I am making a lighting coil charger, however have not bought the OB yet so it may not have a Alternator

 

[sarabande]

OK, I see where you are going.


In very rough terms you can use 50% of an ordinary battery's capacity before doing it quite a bit of harm in relation to the total number of charge /discharge cycles it can tolerate.

You need to add up two figures:

1 the natural self-discharge rate of the battery (i.e. how much charge it loses each day even without any power being drawn from it. This will vary so much between battery makes and types, ambient temperature, state of the battery internals....)

PLUS

2 a realistic sum of your power usage each day.

Back of the fag packet (given that no verifiable usage profile has been given) for the light demands you are placing on it) perhaps a month to 6 weeks. Which suggests that even a small 10 watt solar panel carefully deployed will keep the battery topped up to last much much longer. Even a cheapy ebay one at around £10 will make a big difference to the battery's life - so you won't have to lash out £80 on a new battery at the end of a season.

 

[Pandoramark1]

OK, I see where you are going.


In very rough terms you can use 50% of an ordinary battery's capacity before doing it quite a bit of harm in relation to the total number of charge /discharge cycles it can tolerate.

You need to add up two figures:

1 the natural self-discharge rate of the battery (i.e. how much charge it loses each day even without any power being drawn from it. This will vary so much between battery makes and types, ambient temperature, state of the battery internals....)

PLUS

2 a realistic sum of your power usage each day.

Back of the fag packet (given that no verifiable usage profile has been given) for the light demands you are placing on it) perhaps a month to 6 weeks. Which suggests that even a small 10 watt solar panel carefully deployed will keep the battery topped up to last much much longer. Even a cheapy ebay one at around £10 will make a big difference to the battery's life - so you won't have to lash out £80 on a new battery at the end of a season.

So, if I was to get a cheap 10w Solar panel would I need a regulator, or is it ok to use the cigarette lighter direct into my switch below as there will not be that much power generated from it?

 

[macd]

So, if I was to get a cheap 10w Solar panel would I need a regulator

To paraphrase VicS, who knows about such things (and allow him a lie-in on a Sunday morning):

"One rule of thumb is that up to 1 watt of solar power per 10Ah of battery capacity does not require a regulator but that it is advisable to fit a regulator to panels over 10watts regardless."

So, no. Although you would need a blocking diode. Some panels com with them already fitted: check the spec.

 

[pvb]

After taking all electrical devices into consideration, Lights (NAV's and LED interior) clipper depth and a small compass light I am drawing 0.2A.

0.2A is an incredibly small current for your entire boat. Are you sure it's correct? If it is, I'd question whether your home-made nav lights are bright enough for safety.

Also, your switch panel looks as if it has illuminated switches - have you included those in your 0.2A?

 

[Pandoramark1]

0.2A is an incredibly small current for your entire boat. Are you sure it's correct? If it is, I'd question whether your home-made nav lights are bright enough for safety.

Also, your switch panel looks as if it has illuminated switches - have you included those in your 0.2A?

it is not illuminated just red buttons, I do not have a great deal on the boat but i will be doing A) the figures again and B) a night test tonight to see the finished results for the NAV lights are safe.

Thanks for all the help as usual!! without all your input my Prject Pandora would never have taken off

speak to you all later

 

[VicS]

VicS, who knows about such things (and allow him a lie-in on a Sunday morning):

Cheeky sod.
Operating under a great handicap. Mrs S has gone to stay with the former Miss S for a few days. Even had to cook my own lunch today

However from the top.

So after converting my old NAV light on my Pandora, to my special Home Made LED beauties total cost 90p a light

Sorry to pour cold water on your project but I think you will be lucky if this works satisfactorily.
The trouble with LEDs is that unlike incandescent filament bulbs they do not emit a continuous spectrum.
If you use ordinary LEDs you are likely to find that the they do not emit at the frequency which corresponds to the colour of the lens. You may find the coloured lights very much dimmer than you expect.

It is possible to buy LED arrays that have been specially developed to match the colour of the lenses but because they are specially developed they are very much more expensive. £9 for a festoon bulb replacement for example. They are also powered via a built in driver circuit with the result that the current consumption is rather higher than that of simple LEDs. 0.15 amps each for example

A supplier of the special LED replacements is SEAROLF

Special replacement LED arrays are also available for bicolour and tricolour lights

Ultraleds may or may not now supply them but have been the subject of some bad reports on here in the past.

a night test tonight to see the finished results for the NAV lights are safe.

Remember the colour of the lights is specified as well as the arcs of visibility and luminous intensity.

See sections 7,8 and 9 of Annex I to the International Regulations for Preventing Collisions at Sea

Do you have the equipment and expertise necessary to confirm that your homemade lamps are compliant?

So my question is what is the calculation that will let me find out how long it will take for me to reach a 90% Depth of Discharge based on a 0.2A continuous draw.

I hope this make sense, look forward to your responses and support

As said, unless you have a genuine deep cycle battery, do not run it regularly below 50% of fully charged and also remember that its life is a function of number of discharge cycles and the depth of discharge

Capacity is normally quoted at the "20hour" rate that means at a current that discharges the battery to a specified level in 20 hours. Thus a 110Ah battery will deliver 5.5 amps for 20 hours (5.5 x 20 = 110)

In practice actual capacity available is dependent on the current. The lower the current the higher the apparent capacity and vice versa For a detailed explanation you will have to see Peukert's law
See here

However if you ignore Peukert and limit yourself to 50% of the battery capacity you have 55Ah maximum available.
That is
550 hours at 0.1 amp,
275 hours at 0.2 amps, ( the answer to the question you asked)
122 hours at 0.45amps ( three Searolf LED festoon replacement lamps)
92 hours at 0.6 amps ( four Searolf LEDs)