Charging batteries from engine alternator

[Cardo]

Apologies if this is a daft question, but a quick search hasn't provided an answer!

If one needs to charge the batteries using the engine alternator (say when anchored for an extended period and batteries need a little extra juice) would you run the engine and leave it idling or up the revs whilst leaving it in neutral?

When I leave the engine in idle, the alternator doesn't seem to provide much amperage to the house batteries (just looking at the little ammeter on the panel) however when I up the revs, I start seeing a good 5 to 10 amps flowing into the batteries (depending on what is on and using power at the time).

So if I was sitting on the hook and needed to juice up the batteries by running the engine for an hour or so, what should I do?

 

[Tranona]

Using the engine just to charge batteries is not a good idea. The alternator puts very little load on the engine so prolonged use in this mode can lead to glazed bores and a ruined engine. Depending on the gearing of the alternator drive you need to be running at well over tickover to generate significant charge.

If your expected electricity consumption exceeds what you can put back into the batteries when travelling under motor, then you need to fit alternate power sources such as solar or wind, or use a generator or shorepower.

 

[Cardo]

We're planning some extended cruising where we'll likely be spending many days at a time on the hook with no shore power in sight. We already have a towed/wind genny and will be fitting a reasonable wattage of solar panels, which should hopefully cover our electrical usage most of the time. We also have a decent sized battery bank.

However, I'm just wondering what to do during those times when the solar/wind may simply not be enough for whatever reason and we need to give the batteries some extra juice. I've seen many people mention charging up using the engine/alternator, however I'm wondering what would be the best way to do this without going anywhere?

 

[sailorman]

We're planning some extended cruising where we'll likely be spending many days at a time on the hook with no shore power in sight. We already have a towed/wind genny and will be fitting a reasonable wattage of solar panels, which should hopefully cover our electrical usage most of the time. We also have a decent sized battery bank.

However, I'm just wondering what to do during those times when the solar/wind may simply not be enough for whatever reason and we need to give the batteries some extra juice. I've seen many people mention charging up using the engine/alternator, however I'm wondering what would be the best way to do this without going anywhere?

a small 2T portable genny at under 100 squids

 

[Cardo]

a small 2T portable genny at under 100 squids

Something like this? http://www.machinemart.co.uk/shop/p...0w-petrol-generator-g720?da=1&TC=GS-010610720

Could I then simply hook up the shore power cable to the socket and run the battery charger and potentially other low power 230v items from the boat's mains ring?

 

[testmonkey]

a small 2T portable genny at under 100 squids

that would then be a petrol genny requiring separate fuel source etc...

 

[Cardo]

that would then be a petrol genny requiring separate fuel source etc...

We have a small petrol outboard for the dinghy, so would have a stash of petrol onboard, although wasn't planning to store much of it.

 

[Grehan]

Just to contribute something practical to balance my 'theoretical' parallel thread, we bought a nearly new Kipor 2kW genny about 4 years ago. Very pleased with it. Today it started 4th/5th pull after having sat unused for about a year. Quiet(ish) and smooth.
An obvious point, but don't store petrol inside . . .

 

[Hadenough]

How real is the risk of glazed bores? We are now well equipped with a wind turbine and solar panel which 95% of the time keep the batteries well charged. However, when at anchor or on our mooring we still have to run the engine to get hot water from the calorifier (15mins morning and late afternoon). Heeding the glazed bore threat I run under load (1200 revs in reverse) when on the mooring. What's the view is this enough "load" to mitigate the risk of glazed bores?

 

[VicMallows]

Sometimes, as you say, there is no realistic alternative on a typical boat to running the engine to charge the batteries. (no wind AND no sun for several days is not unknown in Britain ). Portable generators are never much fun on a boat at the best of times either for you or any neighbours.

You want therefore to pump as much charge into your batteries as quickly as possible. That indicates a so-called 'smart regulator' ..... or a manual way of increasing the charge voltage to, say, 14.8v if your skills are up to that. You also need to be able to monitor the charge voltage and current Increase the engine revs just enough to achieve the 'boost' charge voltage. When the batteries have recovered to around 80% capacity the charge current will start to reduce very significantly and you should stop charging. Trying to get the batteries to any greater state of charge will take a very long time with the engine extremely lightly loaded so is not a good idea. Typically I find about 30minutes of engine running will adequately recharge the batteries, but that will of course vary greatly depending on your set-up and useage. (A battery monitor such as the Nasa BM-1 will help your battery management immensely).

 

[noelex]

A lot of crusing boats used to charge their batteries this way.
Alternators vary. Some put out significant current at idle, but others not much. If you are using this method to charge often it pays to change the alternator to a high power model of the former type with external regulation so the charge points are as high as possible.

All you can do otherwise is look at the ammeter and select the best compromise of engine speed and charge rate.
The engine will be very slow to provide the last 20 % of charge so running the battery in the 50-80 % soc range is generally necessary.

 

[lw395]

Get a voltmeter at least.
at tickover, you may find the volts are down, with flat batteries and perhaps the fridge running.
In which case it is worth using a few more RPM.
But once it reaches its limiting voltage, adding more RPM does nothing.
If you have a modern alternator, it is quite likely to give plenty of charge at tickover, but a smart regulator does help.

I am not sure that bore glazing is likely to be an issue if occasional one hour battery charging sessions are interspersed with motoring in and out of harbour every day or two.

 

[Ross D]

You could fit a second large alternator for charging the batteries and only connect it up when you needed to charge the batteries. I would provide a bit more load on the engine and you would charge the batteries quicker.

If you run the engine hard occasionally when motoring it helps to deglaze and de coke the engine.

I normally run at about 60% on my engine which pushes us along comfortably at hull speed, extra revs gives very little extra speed from then on. However, last weekend my daughter was very sick in her bunk and we had to abandon our plans and head home. I keep the boat in a tidal mud berth and had to run flat out up river for an hour and a half, I made it into the berth with 10 mins to spare. The engine exhaust was very sooty when I first put it to 100% but eventually ran clean, hopefully cleaning up the engine nicely.

Ross

 

[Hadenough]

Thanks everyone. We have a regulator fitted and are able to monitor the volts and amps. We rarely need to run the engine just to charge the batteries now and my main line of enquiry was running without load to heat the calorifier. On reflection the times I am running without a load compared to with a load is probably 15% / 85% so I guess I am worrying about nothing. Added to which a couple of exits from the Ore against the last of the flood each year is probably enough to deglaze the bores!

 

[ccscott49]

There is a awful lot of rubbish talked about "glazed bores" Modern diesel engines with modern oils, do not tend to laze bores, we run engines at no load for long periods of time, then use them at full load for a few hours, then they tickover for long hours. I have never heard anything about glazed bores on our engines, in the oilfield for the 33 years I've been in it.

When my genny packe din, I had to run my stb main engine to charge batteries when at anchor, I had no other way. I did this for about six months, on and off, never had a problem with my engine, no "glazed bores".

For me I would fit a dedicated inboard genny, if not then a suitcase kipor/honda type genny, you carry pertrol for your outboard, whats the difference, we are not talking 20 gallons here!
I store my spare petrol, (10 litres) for outboard, in the dinghy, or gas bottle locker.

 

[sailorman]

Something like this? http://www.machinemart.co.uk/shop/p...0w-petrol-generator-g720?da=1&TC=GS-010610720

Could I then simply hook up the shore power cable to the socket and run the battery charger and potentially other low power 230v items from the boat's mains ring?

i have that very machine with different labels stuck on

 

[chrishelen]

There is a awful lot of rubbish talked about "glazed bores" Modern diesel engines with modern oils, do not tend to laze bores, we run engines at no load for long periods of time, then use them at full load for a few hours, then they tickover for long hours. I have never heard anything about glazed bores on our engines, in the oilfield for the 33 years I've been in it.

When my genny packe din, I had to run my stb main engine to charge batteries when at anchor, I had no other way. I did this for about six months, on and off, never had a problem with my engine, no "glazed bores".

For me I would fit a dedicated inboard genny, if not then a suitcase kipor/honda type genny, you carry pertrol for your outboard, whats the difference, we are not talking 20 gallons here!
I store my spare petrol, (10 litres) for outboard, in the dinghy, or gas bottle locker.

+1
an average diesel car/van spends a lot of its life at traffic lights ticking over,
not uncommon to run up sky high mileage.

 

[[2574]]

There is a awful lot of rubbish talked about "glazed bores" Modern diesel engines with modern oils, do not tend to laze bores, we run engines at no load for long periods of time, then use them at full load for a few hours, then they tickover for long hours. I have never heard anything about glazed bores on our engines, in the oilfield for the 33 years I've been in it.

I'm sure that's right. My objection, FWIW, is that the energy (in)efficiency when converting fossil fuel in to stored electrical power via standard engine alternator is really terrible, something mad like a 97% efficiency loss, or 3% efficient. For that reason I've fitted a very large alternator with a proper regulator so that if I do have to run the engine I can shove power in at about 80A or more so only relatively short periods of engine running needed. There's also nothing worse than seeing exhaust fumes spilling over an otherwise pristine morning in a West Country ria scene.