Cheap car batt charger?

Maths may be ok ... but surely the charger takes what ampage it requires as all units incl. chargers are virtual resistors .. so if it outputs 5A at 12V ... actually it's more like 5A at 14V = 70W .... then it will demand 70W + any losses from generator ~ 80W ? ... 240V at 80W = 0.3333A.

Don't believe ? Start the genny and run a light item on it ... and motor doesn't start to really work as demand on alternator is light ... now plug in a near max wattage demand item and motor immediately starts to work hard. Both items rec'd 240V - so waht was different ? Amps draw was different.
 
The analysis is that you with no loss you could transform 240 volts ac with 1000 watts to give you 83 amps ac at 12 volts into a purely resistive load.

You have losses due to inefficiency and power factor.
However, 14 amps means you're only getting 17% of what the power that the genny says it can deliver at 240 volts AC.
This seems a bit grim, but you are getting almost three quarters of the 20 amp max of your Sterling generator - it's not far from maxed out.

A cheap car charger won't deliver the bulk charge rate you are looking for. I think you have no option but to get a beefier Sterling. I'd bet you'd get a much better charge rate even with the present genny. btw You have got the Sterling set up for the right capacity batteries I presume. I recall having to twiddle some internal switches on mine, but it's so long ago that I can't remember the detail.
 
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I'd increase the size of the battery bank so you don't cane it so hard. This will have the twofold effect of being quicker to recharge and lasting longer.

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Didn´t think i was caning it, rarely goes below 70%, thats only using 30% of the capacity. Even calder has 50% as a benchmark.
 
Correct, what peeps forget is that what counts is wattage, less volts means more amps means thicker wires.
Watts are a measure of power and remain constant, 750 watts = 1HP ish, so if a genny is putting out a 1000 watts it means that it will put out 83 amps at 12v or 4 amps at 250v. (OK I kow there are losses in transformers, invertors etc but the theory is the same)
Stu
 
'ang on ! I have never come across a 1000W genny (i.e. 1000W at 240v AC) that also puts out 1000W at 12v.

As Refueler pointed out, the size of the 12v cabling for that power output would need to enormous - bigger than lorry battery jump start cables.
 
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Correct, what peeps forget is that what counts is wattage, less volts means more amps means thicker wires.
Watts are a measure of power and remain constant, 750 watts = 1HP ish, so if a genny is putting out a 1000 watts it means that it will put out 83 amps at 12v or 4 amps at 250v. (OK I kow there are losses in transformers, invertors etc but the theory is the same)
Stu

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It does not put out 1000W regardless ... it puts out what is asked of it.

Think of your house with KW's coming in ... be a really bright light if it was given KW's instead of the 100W it asks for !!

The genny is running light when not connected ... no watts being output at sockets ... only light wattage used by engine itself. Plug in a tool and engine then loads up and works hard to meet genny demand to supply whats needed by tool.
If your 1000W was delivered - I would never ever plug my 300W grinder into my 700W genny - I'd be asking for trouble.
 
Sarah
you miss the point, I didnt say that. A 1000 watt genny puts out 1000 watts at 250 volts (ok 230) for the purposes of the argument!
If you had a 12 volt charger that was capable of putting out 83amps then that is what the genny is capable of driving. ( By the way I aint going to argue about power factors, inefficiencies etc!)
The point I am making is that one should always look at wattage as the constant, 750 watts equals 1 HPish. 1000 watts = 1.25 hp. A small petrol genny is more than capable of "driving" a 12v charger of quite high output
Stu
 
Sarah
I answered the first part of your post, the second bit, think about it, a wagon starter uses 100s of amps. In actual fact if you look at our modest alternators you will see a red cable coming off the back, this is the main output. On my MD22 with a 70 amp alternator (boosted by a Sterling) it is only about 6mm diameter, the alternator is usually putting out its maximum at start up and the cable is adequate to cope with this. So why do we need a wagon starter cable to carry 80 amps?
Stu
 
I had the same idea as the OP. Bought a 25A charger from a mobility scooter shop. On shore power it charges at 25A. Plug it into my cheap 800W genny and charges at 10A. Genny has a an 8A 12V output which usually charges at 10A - so no benefit in charging through the charger. You might do better with a honda genny as it's more likely to give you a sine wave output.
 
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I had the same idea as the OP. Bought a 25A charger from a mobility scooter shop. On shore power it charges at 25A. Plug it into my cheap 800W genny and charges at 10A. Genny has a an 8A 12V output which usually charges at 10A - so no benefit in charging through the charger. You might do better with a honda genny as it's more likely to give you a sine wave output.

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This is probably caused by indifferent design of the charger and the voltage of the generator dropping under load.
What is needed is a small petrol engine driving a hefty '12V' alternator or two?
 
James, I said that IF the charger has a 100% efficiency.
I fully agree that this is not the case. The reason I did this was to keep the example simple. The statement that a 1000W genny can power only a 12V 4,5 A charger is just not correct. This I was trying to explain. That I was not able to explain this clearly is my fault.
 
Another thing to factor in, sine wave. SDMO sell an invertor genny, £260ish, as good as a Honda but a lot cheaper, made in France. It drives my Dolphin on board charger as good as mains power, hence my earlier posts. Point is that a small genny IS capable of driving hi power chargers, and that peeps need to concentrate on the POWER of a genny, ie watts
Stu
 
Nige
my new SDMO genny is rated at 750 watts, peak 900 watts, I have a 720 watt toaster on board, swmbo is a v happy bunny, it works the toaster fine, it doesnt like the water heater though, my next quest is to find a 500 watt element for it.
The point I am making is that the smallest of gennies, with certain caveats can drive/put out a lot of 12v amps!!
My mission was to get peeps to understand the watt thing!
My analogy is a water pump ad pipe, the smaller the pump the bigger the pipe needed to get the same amount of water through in a given amount of time, if the water is the watts, then the size of the pipe is the amps and the pump is the volts.
Stu
 
Just to add some real numbers to the discussion of charger efficiency, I checked my own charger.

It is a heavy duty charger, not a cheap one as originally mentioned, and can charge 12v batteries at 15A DC. It is rated at 310W on 230VAC although it may not actually used this when charging as it can also be used to start an engine. Anyway, the power going in is not more than 310W and it can charge at up to 180W (12V x 15A). Therefore it should be at least 58% efficient. It is also well within the range of a 1,000W generatoralthough there may be some reduction in efficiency due to the modified sine wave.
 
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Nige
my new SDMO genny is rated at 750 watts, peak 900 watts, I have a 720 watt toaster on board, swmbo is a v happy bunny, it works the toaster fine, it doesnt like the water heater though, my next quest is to find a 500 watt element for it.
The point I am making is that the smallest of gennies, with certain caveats can drive/put out a lot of 12v amps!!
My mission was to get peeps to understand the watt thing!
My analogy is a water pump ad pipe, the smaller the pump the bigger the pipe needed to get the same amount of water through in a given amount of time, if the water is the watts, then the size of the pipe is the amps and the pump is the volts.
Stu

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I don't dispute a genny supplying the watts .. I have 2 gennys - the 700W Wolf and a 3.5KW Briggs & Stratton - they will supply the stated watts without problem.

What I was posting was that a genny will supply what is DEMANDED of it UP to its max setting - when the trip will usually operate. The operative word here is UP to ...

I run a car charger sometimes of my 700W job and it still only supplies 4A when battery is low. Same as when on normal mains.
If OP could find a cheap 50A car charger - it would work as long as genny is clean AC ... no doubt. But 50A car charger is a rare beast indeed.
 
Thought you may find this helpful:

Battery Chargers:

There are two main types you are likely to come across in the marine market. The first is a ferroresonant automotive type (Halfords, Gunson, Snap on etc etc). They are cheap and simple but not designed to rapidly and safely recharge large capacity battery banks.

By having a fixed voltage output of 14V they will commence charging at close on their maximum output. As batteries charge, their internal resistance increases, this means that the charger finds it harder to push power into the battery. This is why you see the current starting to taper off down to a trickle. They will only ever get the battery to about 80% charged.

Proper marine chargers (Dolphin, TrueCharge, Mastervolt etc) do not have a fixed voltage output. By carefully controlling the voltage, they are able to overcome the internal resistance of the battery. This means that during the first phase of charging (bulk charge), you will see a continuous output of the charger's maximum rating. This continues to around 80% charged. At this point the charger's output voltage will be as high as it is safely possible to go (Called Absorption phase). It will therefore hold the voltage up high (usually 14.8V for a cold lead/acid battery) and the current will reduce. This brings the battery to up to 100% charged. At this point, the charger then reduces the voltage to 13.2V as a float voltage.

This is why it's a false economy to run a car charger from a generator (or use the limited DC output of a generator). You will have to run the generator for hours to get any meaningful charge.

The next thing is Power Factor Correction (PFC). This is a very complicated subject. In laymans terms, PFC ensures that that the charger is as effecient as possible when running from the 230V supply.

Generally speaking, it is very difficult to Power Factor Correct a transformer. Automotive Chargers are transformer based (generally) and do not have it. Their Power Factor can be as bad as 0.5. A good quality, switch-mode marine charger with good power factor correction techniques can be as high as 0.9.

So, to work out approximate wattage draw from the generator.

Charger = 50A. Charge Voltage = say, 14V = 50 x 14 = 700 watts. Now divide by the Power Factor:

A 50A non corrected unit will pull: 1400 watts
A 50A PFC charger (0.9) will pull: 777.77 watts

I noted in the posts above, the outputs of the generators. I used to sell Honda generators until quite recently. The EU10i and EU20i (and most of their competition) provide around 5 or 8A charging at 12V. Thats all - its not that well regulated either.

So I go back to one of my earlier posts in reply to the original poster - you already have a Sterling 20A charger. Use that not the 50A automotive unit. You'll save yourself money in terms of generator fuel and your neighbours will thank you for not running the generator for hours and hours.

James
 
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