Enough power for instruments?

[lockwood]

I have recently been given a set of 4 NASA instruments for a birthday present: Target wind, compass, log & depth.

My small boat (Jag 22) has just one 80ampH and is charged only with a 8hp Mariner outboard.

As well as the instruments above, the battery also powers the running lights (1x bi-light at bow & 1x stern light).

So far, I have had no problems and the battery seems to get sufficient charge from the short bursts of motoring.

I am now thinking of adding 2 x interior cabin lights (halogen) and possibly a stereo. Will this drain the battery a lot more? If so, would a small solar panel be beneficial?

I remember seeing a simple formula which helps to work out power consumption but can't find it now.

 

[simonfraser]

get the led lights, use far less power, a small 30w solar panel has worked fine for my boat over the last two years, same instruments.

 

[ShipsWoofy]

To work out power we use Ivy Watts, she is a great formula.

I (current) x V (voltage) = Watts

Or transposed

Lets say you have 10W bulbs in your navigation lights. 2 lamps so 20W

From the above formula we would get I = W / V

so 20 / 12 (for sake of argument, though if you keep your battery fully topped up this might be 12.6v or slightly higher)

so I = 1.66A

So overnight lets say 7 hours in summer you will use 11.62 Ah approximately. This is very simple, there are other variables, but for the figures you require it should be an adequate way of measuring the current on board. If you are worried it may be worth buying an ammeter to monitor your day to day use and a voltmeter to have a constant check of the state of charge on the battery.

Hope this helps

 

[Sea Devil]

Bet you find the stero if it has a cd player will eat amps like mad.

Always a difficult decision but the more batteries you have the better - I would ad a 2nd 80 ah first - then your basic capaicity to run things, particlaly at night, is much better. If after adding a 2nd battery you find there is not enough capacity then add a solar panel but out of the tropics/Med it will only keep the batteries topped up when you are off the boat - very unlikly to put in enough during the day to compete with running your motor for one hour.

The nasa insrtruments will pull very little but the lights will probably be an I ah each, Nav lights the same or slightly more, Stero could be up to 4 amh! you add it all up then x by hours running and thats the total but you should count on only about 1/3 the battery capacity so if you add a 2nd battery of 80 you will have around 50 Ahours to play with......

 

[lockwood]

what about one of these VHF/FM receivers. Obviously it can only be used for radio and not CD, but that would be fine.

http://www.yachtbits.com/gme_audio/gme_gr100_fm_mw_lw_sw_and_vhf_receiver.php

Would this 'eat' less of the battery? I have tried to find a website for the manufacturer but have had no luck.


Also - I agree about using LED lamps for the cabin. The problem I have with that is that I can only find disc shaped lamps, nothing on a pivot. Anybody know of a retailer for LED lamps that pivot?

 

[FullCircle]

As a long term small boater meself (Jouet 23ft) I have used a similar setup to yours, but I went for the small fluorescent lamps at the local boat jumble (new) for about 5-8 quid each. These are 5 to 8 watts. LEDs are a bit dearer. I also fitted a second battery and an isolator. I always buy the batterys from car breakersa at a fiver or so each. Sometimes they last 3 months, one I had lasted for 3 years. Pot luck, but way cheaper than new at 35 quid or more (deep discount).
I had my charging from a Yamaha 6hp and it usually kept up until 2/3rds through the season. The biggest drain appeared to be my VHF on watch. Also use a kerosene hurricane lamp (6 quid off ebay) for anchor lights.

A 25 watt bulb is about 2 amps, so a 5 watt bulb is about 0.4 amps. Remember that you only have access to a tad over 50% of the batteries rated ampere hours ( I wont go into why, it just is).
Happy Sailing.


Jim

 

[Joe_Cole]

I would not fit a second battery as your outboard engine is only churning out about 6 amps. It's enough to keep one battery charged, but will never manage 2 batteries. One well charged battery is much better than two badly charged, and therefore deteriorating, batteries.

Fit a solar panel to ensure that the battery is charged up when you are not on board.

Apart from that just avoid excessive use of your electrics and you should have no problem.

The biggest drain is lights and CD; just be careful with them.

PS The radio you linked to was featured in an article in PBO (I think) a few months ago. It had a poor report.

 

[William_H]

No don't worry about current drain. It all depends on your actual use patterns. For example I will bet that you will only use your cabin lights for short periods ie to find something. If you like reading at night in the boat that is a different story. You possibly like me don't use nav lights very much either. If you become concerned about current capacity on a particular trip you can do without a lot of the stuff ie instruments unless you really need them. regarding a steroe. Most have digital tuning with a requirement for 12 v supply at all times to maintainin tuning memory. This is a real problem as it will flatten your battery over a week or 2. If you disconnect the battery you have the tedious business of retuning each time you go to the boat. I prefer an old fashioned manual tuned car radio. Of course if you want CD stereo then you will probably end up with digital tuning and have to put up with retuning the radio. I have used solar as only charging for many years.(lots of sun) It is tied on to the boom sail cover and is removed when sailing on a boat similar to yours. I wouldn't suggest you do so however unless you are having flat battery problems. Don't panic about flattening your existing battery. It may shorten it's life but is still cheaper than the alternatives of more batteries on the off chance you may discharge your one battery. Lets face it none of your electrical loads are really essential. regards will

 

[Joe_Cole]

[ QUOTE ]
. Most have digital tuning with a requirement for 12 v supply at all times to maintainin tuning memory. This is a real problem as it will flatten your battery over a week or 2.

[/ QUOTE ]

I think it depends on the radio. Mine has a memory for the presets but the power demand for this is very, very low so it isn't a problem. It does mean however, that the memory wire has to be connected direct to the battery, which I don't really like. I did connect it though: anything to avoid setting the presets each time I switch on!

 

[William_H]

Yeah I think you may be right Joe mine is only about 14AH battery (NiCad) with a 3watt solar panel. Even in Oz summer sun the radio soaked up all the solar power or at least seemed to perhaps it was just a poor radio. Disconnected radio electrics are now fine. Something tio watch for anyway. will

 

[Guest]

Radios etc.

There are plenty of cheapo radio combos in the shops that take mains / battery. The 29.99 specials that Argos / Dixons etc. do often are 12V from the battery compartment. So - drill a hole in the battery cover for a cable to run and supply 12V from the boat system. OR ... a simple piece of dowel replacing the batterys with drawing pin studs on ends with wires attached .... led out again to boat supply. These radios also normally have manual tuning and not digital .... meaning it stays tuned where you leave the dial !!

As to general battery / useage etc. Outboard charging is OK for simple low level day-boating / weekends etc. but is not ideal for extending battery unless you do a lot of motoring etc. A small solar panel .... available in car accessory shops for keeping batterys topped up can be useful - BUT WILL NOT 'CHARGE' A BATTERY FROM FLAT / DRAINED condition ...... they only mantain a charged battery .... we are talking the 5W trickle solar jobs at about 29 quid. I used them and found they worked .... but are not so tolerant of being left in all weathers ... mine lasted just over 18 months before the crystals crazed.
If you fit a higher rated solar .... 10W or even better 15W - there is no reason that this should not help you - but again is really for when the boat is standing at berth / mooring to maintain the battery ready for when you go sailing. You can of course spend money and go for a real duty job that will charge and do a fab job .... but what are you really looking for ?

Your instruments you talk about will not drain too much of the battery, and the cabin lights are only usually used on limited basis .... a walk around a Caravan Store and chat with the sales guys will point you to some items ... advise him that you want low current drain but maximum light etc. While you are in there have a look around generally - you'll be amazed what you see and how you can use them ..... small white caravan corner lights ... excellent cockpit lights ! etc. etc. Not only electrics but water systems / loos / all sorts.