vic008
Well-Known Member
Running engine for charge for battery. Sometime down to under 5A,(sometime over 40A) when do you decide not worfh running the engine for a paltry charge.
At what Amp not worthwhile
- Thread starter vic008
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ChromeDome
Well-Known Member
I'd consider the battery health. There'd be an optimal charge regime depending on type/size/use pattern.
What battery setup do you have? Solar being an option?
What battery setup do you have? Solar being an option?
vic008
Well-Known Member
Solar and nextstep alternator regulator. Am beginning to think that overcast rainy days see the alt put out 40A to start ,then taper down to 10A and less over an hour. Whereas a sunny day will see alt put out only 5A or so. And I wonder whether worth running the engine for that
Tranona
Well-Known Member
That is quite normal. The charge rate is determined by the battery acceptance rate not by your charging source. Depending on the size of your bank 5A suggests the batteries are close to full and the acceptance rate is slow. Using the engine is not a good idea unless you have it under load, for example actually using it for propulsion. 5A is no load at all on the engine. Just let the solar finish the charging (slowly!).
pcatterall
Well-Known Member
So, in general terms, is it better to run engine for a short time ( perhaps until charge rate drops from 40 to 30 then repeat as battery becomes depleted?
Tranona
Well-Known Member
No. Running an engine for charging batteries is not a good idea unless you are putting another load on it, for example by running in gear in a marina berth. Most of the long term problems with small marine diesels are the result of short period low load running when the engine never gets up to full operating temperature and does not fully burn fuel. You can see the effects in coked up exhausts and valves, excessive bore wear and sort oil life.
Appreciate than many people do use their engine for battery charging, but far better to use an alternative such as solar, wind, generator or shorepower.
fisherman
Well-Known Member
I never really understand, but am told the alternator is designed to put in a quick top up charge to replace start current in a car, and can only charge a battery to about 75%, although it will say it is full. My friend installed Adverc, his engineer said very unusual to see a battery so comprehensively charged, 95%+. I believe a generator, as fitted to cars in the olden days, or portable etc, will do the job, as will solar or wind.
I only had a 40 amp alt in my boat. No point having bigger, the total draw could only reach 32A. The problem is it needs to get to about 3000rpm, so if the engine was under 1000rpm the current declined, so having 70A or 100A no point.
I only had a 40 amp alt in my boat. No point having bigger, the total draw could only reach 32A. The problem is it needs to get to about 3000rpm, so if the engine was under 1000rpm the current declined, so having 70A or 100A no point.
Buck Turgidson
Well-Known Member
When I did my 1500nm trip from uk to med I tried to run the engine in the morning when the battery was at its lowest charge state. Run for 30 min- 1hr with the engine in gear for load. This bulk charged the battery, then the solar throughout the day would float charge so that at sundown the battery was fully charged. It worked well and conserved fuel by getting best amps per unit fuel as well as kept the battery healthy. Unless you have a very large battery bank or very expensive lithium then a normal 30-50a alternator is perfectly fine.
Buck Turgidson
Well-Known Member
If you needed 3000rpm your alternator pulley was too big.
fisherman
Well-Known Member
Alt 3000, not engine. 1000 on the engine, =approx 3000 on alternator. I thought of a smaller alt pulley but it would have crippled the belts
Tranona
Well-Known Member
Similar to the way I do it when cruising, except I don't have solar. Always try for around an hour motoring which usually puts in over half of what is consumed during the previous day and overnight. You often hear people boasting about how they raise sails and shut down the engine within minutes of leaving their mooring. Nothing could be worse for their engine and batteries. You are right about alternator size - my D1 30 in the old boat had a 115A alternator but never saw more than 40A as the 270Ah bank could never absorb a higher charge rate. New Beta 30 has 75A alternator, more than enough.
Neeves
Well-Known Member
It depends on the size of your battery bank, the size of your engine, the output of your alternator.
I suggest you record revs vs amps, turn the engine revs down so that the revs produce the number of amps that the batteries accept - but note Tranona'a comments. Better to re-charge when you are motoring, not when you are at anchor.
In order to keep the engine working, a bit, when you are re-chasrging the batteries and the acceptance rates is dropping - use the power that the battery will not accept to freeze down your fridge, recharge all your electronic devices, bake bread in a bread maker etc. But remember to turn the thermostat in the fridge up (now that it is icy cold). If you don't have many electronic devices, iPad, laptops etc - find some grandchildren
We do the same as Tranona and Buck - we are not purists - when we 'leave' the sea to enter a bay (where the wind inevitably drops) we do so under motor. We drop sails and anchor under motor. The following day we reverse the procedure (except we raise the main at anchor) and motor out to the sea - where hopefully we sail (not motor).
Jonathan
I suggest you record revs vs amps, turn the engine revs down so that the revs produce the number of amps that the batteries accept - but note Tranona'a comments. Better to re-charge when you are motoring, not when you are at anchor.
In order to keep the engine working, a bit, when you are re-chasrging the batteries and the acceptance rates is dropping - use the power that the battery will not accept to freeze down your fridge, recharge all your electronic devices, bake bread in a bread maker etc. But remember to turn the thermostat in the fridge up (now that it is icy cold). If you don't have many electronic devices, iPad, laptops etc - find some grandchildren
We do the same as Tranona and Buck - we are not purists - when we 'leave' the sea to enter a bay (where the wind inevitably drops) we do so under motor. We drop sails and anchor under motor. The following day we reverse the procedure (except we raise the main at anchor) and motor out to the sea - where hopefully we sail (not motor).
Jonathan
geem
Well-Known Member
Those people probably have a decent amount of solar. We never consider using the engine to charge batteries. The solar does it all. We were on the marine park moorings in Bonaire for three weeks with fully charged batteries courtesy of sun and wind. We sailed off the mooring for Curacao. No engine needed. Batteries went to float by lunchtime even with the autopilot and electronics additional load.
We have been on the boatyard pontoons for a week doing jobs. No battery charger needed. We turn the power on to cook on the induction hob whilst we have shore power but that's it. It's great to do your bit for the environment with boaty renewables ?
Tranona
Well-Known Member
That is fine for you and you have organised your charging to suit your pattern of usage and have enough space to fit solar - plus of course you are in a location where you have potentially far more sun.
The OP on the other hand is in Christchirch NZ and from what he says is not a liveaboard and has a much smaller boat - and I would guess knowing the area uses his boat in a similar way to many on here in the UK. He says his solar is not sufficient and he is reliant on the engine for at least some of his charging. So different problems and environment need different solutions. His question was about running the engine just to top up the batteries which is not a "good thing". There are a number of ways of minimising the need to rely on the engine but without knowing the details of his boat and systems, his pattern of usage and consumption plus other resources available, all one can do is make generalised suggestions.
geem
Well-Known Member
I was commenting on your lack of solar. The UK is a great place for solar in the summer. Long daylight hours even with overcast skies put good amps in to the batteries. You don't need the Caribbean to make very effective use of solar
William_H
Well-Known Member
New Zealand aka the land of the long white cloud. So interesting to see what use solar is. I think OP is looking for an answer to a question he will answer on a case by case day to day situation. I would accept less than full charge to the battery rather than run the engine with meagre charge rate. Op is right to observe actual charge current as an indication of time to shut down engine. However if he is relying on engine charge an additional battery in parallel will soak up more charge from engine albeit still leaving now 2 batteries not fully charged on shut down. ol'will
Tranona
Well-Known Member
I don't have solar - in fact I removed it and the Rutland as soon as I bought the boat. Why? simple I only go away for 2 or 3 days at a time and have shorepower when I get back. My house bank is sufficient for that sort of usage. Quite normal here on the south coast not to have solar. I did a count recently in our club which has 350 cruising boats in the marina and a further 60 on moorings and less than 20 have any significant solar (and a few have wind). Almost all of those are boats of the type that owners take on long cruises and want to be independent of shore. The majority of the others like me do weekends and a couple of longer holidays and considering that typically 30-40% of time "sailing" is under motor and plenty of marinas and harbours with shorepower keeping up with power usage is not a problem.
Would guess that most of my fellow club members are capable of working out whether there is value in having solar and have decided against it. A bit like the debate on lithium batteries where the advocates only ever talk about what they can do but never seem to ask the basic question about whether it meets the individual's specific needs. Sure, I can get lots of amps in the summer from solar - but what would it do with them? when my modest bank is already full from the overnight on shorepower when I get back from a few days away.
Not against solar and if I had intended to use the boat for long cruises, I would have kept the davits with panel on top and the Rutland - a very good setup. But I am not going to do that so why keep things I don't need (plus the davits would increase my berthing fees by £300 a year!)
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Many alternators are regulated back too early because they sense voltage at the alternator. To be effective an alternator needs a decent regulator that senses voltage at the batteries. This by default deals with any voltage drop between alternator and batteries. I apply Nigel Calder’s 80% rule - never engine charge batteries after 80% capacity is achieved because it’ll be absorption/float charging at very low current, a cost and environmental disaster.
Alan S
Well-Known Member
You need a decent amount of solar ; )
(Actually this boat has solar electric propulsion).
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Birdseye
Well-Known Member
5 amps at 12v is 60 watts which is less than one tenth of 1 bhp. So you could easlily be converting 98% of the diesel you are burning running your engine into surplus heat and 2% into leccy in your battery.
The answer is that its never worth running your engine just to charge the batteries unless you are in danger of the batteries getting too low to start the engine. Even 40 amps is only just over half of one bhp.
The answer is that its never worth running your engine just to charge the batteries unless you are in danger of the batteries getting too low to start the engine. Even 40 amps is only just over half of one bhp.
