one for the lecky's

[KREW2]

one for the lecky\'s

Hi
Without having to give all the technical data I'm sure there must be a general rule of how long to run the engine, and at what intervals to recharge a battery on a passage assuming I would be running a radio and GPS.
thanks KW

 

[Anonymous]

Re: one for the lecky\'s

The simplest general rule is not to discharge your batteries to more than 60% of their rated Ahr capacity. So, if your battery is 100Ah and you are drawing, say, 5A then after 8 hours you will have used up 40Ahr leaving you with 60Ahr remaining (i.e. 60% left).

If you discharge at a rate higher than C/10 (also called the 10 hour rate) then the 100Ahr battery will not yield anything like 100Ahr, but more like 60Ahr or so. In which case, treat it as if it was a 60Ahr battery when deciding how often to recharge. The latter might become important at night with nav lights, autopilot, etc., etc. The 10 hour rate is the rate of discharge to fully discharge the battery over 10 hours - nominally 10A for a 100Ahr battery.

 

[RickMoss]

Re: one for the lecky\'s

What sort of engine do you have, and more specifically do you know what the capacity of your alternator is?

Your VHF and GPS current requirements will be pretty nominal (except when transmitting on your VHF, but this is very short-term). Allowing 1amp to cover your general running (instruments + radio) would be generous, and the smallest alternator you are likely to have is 35A. Therefore the watts used in a 10 hour passage would take circa 40 minutes engine running to replenish.

Your domestics tend to impose a far higher load on your batteries. Each interior light will draw around 1amp. I also use an inverter which draws anywhere up to 30amps (300 watt inverter).

 

[TigaWave]

Re: one for the lecky\'s

If you're planning on a few long passages then invest in a towed generator, save your deisel for when you really need the motor.

I never needed the engine to charge batteries with an Aquair 100 behind us, we ran the fridge full time and never had a shortage of power.

Its great feeling like you never have to worry about power useage.

 

[john_morris_uk]

Re: one for the lecky\'s

With respect, a 35 amp alternator will only give 35 amps under the most favourable of circumstances. ie when the battery is completely flat and when the alternator is cold. As soon as the alternator warms up, and the the batteries have any charge in them, their internal resistance rises and you will be lucky to get ten amps out of the alternator into the battery - especially with a standard alternator regulator.

Furthermore, you need to allow for inefficiency in the chemical process in the battery. Some energy is lost due to gassing and heating the battery as it is charged. You need to allow for 10-15% 'extra' charge to make up for amp hours used.

 

[Guest]

Without all techy stuff ....

Most boats would need a couple of hours a day engine use to top up batterys ..... that means topping up the act of starting the engine + average low -mod power drain on batt's .... should you run nav lights / start really using domestic power a lot - then thois increases dramatically and you could be looking at 4 - 5 hours a day engine run ....

On a 4 day stint with my boat ...... 45A Alternator, 2 x 100 A/hr battery .... usually my batts are not fully charged at start ... I survive with about 2 hrs a day on engine ..... which covers approach / harbour motoring, berthing etc. - so is really not so much more than would be run by engine anyway .....

Hope that helps .......

You will be advised to carry mutli-meters etc. as check .... good idea - a reasonable multi-meter is a treasure on a boat .... but I actually use a cheap Halfords LED Battery checker ... 9.99 ..... this when used correctly has helped me solve a lot and also told me about batts simply and quickly ..... no having to remember any numbers / data etc. Read the blurb on the side next to the LED's ... simple to use, and despite many people saying differently - mine has been accurate ..... (for other jobs I have the digital Multi-meter ...... about 15 quid ex B&Q ..... )

 

[jerryat]

Re: one for the lecky\'s

Hi Tigawave,
Entirely agree. We use an Aqua4gen towed unit, and it has been one of our best investments on the boat. As you say, loads of amps fighting to get into the batteries, 'fridge on 24/7, no worries about lights etc etc. Wonderful! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

Cheers Jerry

 

[KREW2]

Re: Without all techy stuff ....

HI
Many thanks to all for the advice. I have a volvo 2002 and 2 110ah batteries, one I only use for starting I also have a sterling 20amp battery charger in the system as I am now on a swing mooring I tend not to motor so much, and do not have access to shore power.I only use 1 battery when sailing and switch to both when motoring. If we go out for a full day ie. 8 o'clock start back at 8ish I was hoping just a couple of hours would be enough to re charge.
Thanks again
Keith

 

[Guest]

Normally ok ...

You should be ok with it ... seems that I survive and my boat sits for months without charge etc. Using the regime I gave - I still have some juice left to start engine .... once started of course the alternator then starts banging into the batterys for all its worth.

If I have a day or so spare before using boat - I fly into UK and literally jump on as soon as I can ... then I clip on a Halfords Charger .... a good one with the float facility .... and charge up for the day or so just to make sure.

So my advise .... if possible at intervals try and get a charger connected to them .... as short boost charging as an alternator does is not so good to a battery ... having it charged up full and alternator then - thats a different matter as the regulator will reduce the input to the battery etc. It's a pain I know to lift them on / off .... but maybe when you tie up in a marina etc. - take advantage of electric and stick the charger on ... If I can - I try and hook up whenever possible unless it's silly money like some south coast marinas I can think of .... one wanted 6 quid a night hook-up !! considering I only wanted a few amps to charge batts - that was refused ...... 1 - 2 quid OK ... but 6 ??????

 

[dulcibella]

Re: Normally ok ...

My Duogen water turbine seems to put out 7 A at 6 kt, so running the engine to charge batteries on passage is a thing of the past. It converts to a wind turbine on a mooring. Strongly recommended.