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a3xloser

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can someone help, i need to run a generator to power a battiery charger on my boat, they come in many sizes how can i tell if the generator can power the charger, for example
what amp charger can a 700 watt generator 5 amp 15am 40 amp?

or the other way round the 40 amp charger i want, how many watts will the generator need to produce
thx
 
40 Amps at 14V is 560W.
Your battery charger will not be 100% efficient, but on the other hand, as you will notice when you run it from the mains, batteries rarely draw 40A (or anywhere near) from a 40A charger.

If you have the charger's datasheet, it should give an input current.
This will probably be more than simple calculation suggests, because it's current draw is not a perfect sine wave in phase with the voltage.
 
a3xloser said:
can someone help, i need to run a generator to power a battiery charger on my boat, they come in many sizes how can i tell if the generator can power the charger, for example
what amp charger can a 700 watt generator 5 amp 15am 40 amp?

or the other way round the 40 amp charger i want, how many watts will the generator need to produce
thx
Click to expand...

It depends on the true rating of the generator. Some generators tell you what power factor the rating is at however some do not. Usually it is a theoretical figure for when the generator is at a power factor of 1.0 .

Power factor is something to consider in AC circuits. It is more usual for the power factor to actually be less than 0.70 which means that a 700 watt generator may max out when only delivering about 490 watts. You need to study the specs to see if they mention the Power Factor (Pf).

Your 700 watt machine will probably handle the 40 amp charger which in reality will be delivering less than 40 amps anyway. Depends how near the truth the rating really is.
 
its been put to me that many chargers will only run off a pure sine or modified sine genny, think they call them inverter gennys and are much more expensive,
so is this right i cant use a cheap machine mart 700 watt genny that sells for about £90?
 
Many cheap chargers are dependent on getting an accurate 230V to give an accurate 14V for charging. That is likely to be more problem than the purity of the waveform.

What exactly do you want from this?
If you just need to occasionally shove some charge into the batteries when there is no mains, why not look for a cheap generator with a 12V output?
I have one, it cheers up flat car batteries fairly effectively.
£70 well spent ages ago.

If you are looking at a serious long term regular use kind of system, then maybe matching a genny to your existing charger needs careful looking into.
If your charger is a high tech one, rather than just a chunky transformer, getting info from the manufacturer would be a good start.

If you just want to keep the batteries topped up, you won't need 40A, unless you are drawing a big load from them, or letting them go pretty flat.

However, if you are running fridge, lots of lights, 12V tools or something, that's different. Your shore power charger is possibly sized for that?
 
There was some suggestion in a thread some time ago, that cheap gennys wouldn't power a charger. I tried my (£90 on a Wednesday at B£Q), 1000w generator with my 40amp charger, and it was fine. I've no idea what amps the charger was producing, though.
 
I seem to remember reading somewhere that most marine chargers were happy with output from almost any old generator. I've certainly never had problems running a marine charger from either of my generators (except when the charger was just too big).

Could be something I'm remembering incorrectly. In fact I'm now starting to think that my previous charger's manual said that it had been designed to work with the output from poor quality generators.

I can confirm that a Yamaha EF600 did power my 20A charger but wouldn't cope with a 40A charger. No big surprise there though. A Honda 10Eui and 20Eui will manage 40A charger. As mentioned, just check genny cont. output and charger power requirements ex. manual. 700W sounds about as low as you'd want to go as most genny's usually quote a lower output for cont. use. It won't be at full chat for long but you do want to be able to charge a pretty flat battery just in case.


Of course the OP could always connect a 700W inverter to his charger and power that from the battery. But then some people believe all the free power schemes you see on eBay (good for a laugh though. ;^)
 
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In the canal boat forums there is a similar discussion. And the fact that some things are switched mode seems to mean that a generator won't power something you might expect it to.

I don't begin to understand it, and don't know if it's the generator that might be switched mode, or the charger. I don't even know what switched mode is :(

My 80A charger provides all 80 Amps when it starts up in bulk charging phase. Only when the voltage reaches its regulated limit does the Ampage delivered begin to fall. My 25A charger does the same, (25A, not 80A :) ).
 
The cheap, basic gennys (usually rated 750/850/900W) will at least be putting out a reasonable sinusoidal waveform. The frequency may not be spot-on but this is unlikely to worry most equipment (if you have a meter which can read frequency, simply adjust the speed on the governor to achieve 50Hz; the precise voltage is arguably of less concern for modern electronic equipment)

I would actually have more concerns about a poor quality inverter type genny driving a fussy switched-mode charger.
 
Richard10002 said:
In the canal boat forums there is a similar discussion. And the fact that some things are switched mode seems to mean that a generator won't power something you might expect it to.

I don't begin to understand it, and don't know if it's the generator that might be switched mode, or the charger. I don't even know what switched mode is :(

).
Click to expand...

What does "switch mode mean" well unfortunately the term can mean a lot of things. However in general terms a simple example is to dim a light 12v DC. You can fit a transistor which acts like a variable resistor and dissipates some of the power in heat. At 1/4 lamp power the transistor wastes as much power as the lamp. Then someone figured that if you turned the lamp off and on at a high speed and vary the ratio of on time to off time the transistor does not dissipate any (or much) power because it is either fully on or fully off. So saving power and the concern about cooling the transistor.
From there things moved on. Power supplies for electronics and for battery chargers need a low voltage. this was provided by a heavy transformer with lots of iron and copper. The switch mode power supply takes the mains voltage and rectifies it to DC about 380 volts.This is rapidly (200khz) switched to make a crude AC which goes into a small transformer. It is much smaller because the frequency is so high.
This low voltage AC is then rectified. Amazingly this is cheaper than a large frequency 50 hretz transformer and it also has the ability to be easily regulated to exactly the required DC output voltage.
One of the difficulties of this device is that the current taken from the AC mains by the rectifier is only taken in bites at the peak of the AC wave. The depth of the bite depending on the power required by the device. It seems that in huge total power of a mains system these bites don't matter much. However if you are powering your device from a local low power AC source (inverter or gen) the bites can matter.

When we come to inverters 12v to 240v. The early ones again used transistors in an oscilating circuit to produce sine wave into a transformer. But the transistors in varying their resistance wasted as much power as they switched.
It was easy to turn transistors on and off to switch the DC built up to 240v DC by a switching transformer circuit at 50 hertz rate but this produced not a sine wave but a square wave AC. For incandescent lights and heater even brush type electric motors this didn't matter but not good for induction motors and computers had variable results from this waveform. The square wave can be modified in timing to more look like a sine wave (modified sine wave) but this is more an advertising gimick than real help.

A far more complex inverter assembles the AC sine wave out of chunks of high voltage DC again built from switch mode transformer supply. The bursts of DC are varied in length of time and are smoothed (slurred) to resemble a sine wave. Hence your true sine wave inverters.

Then we come to generators. The old ones and big ones ran at 3000RPM or 1500RPM or even 750RPM and generated the sine wave by the rotating action of a magnet pole past a coil. It is not so good to have a small petrol engine running at high speed (3000RPM) when there is little load. Why not generate DC (actually ac rectified) and feed an inverter circuit to provide AC. This means engine speed can be what is required for the power needed. ie slow for low demand high for high demand.
However the inverter may or may not produce a sine wave which many devices demand.
Does this help or confuse. Switch mode to analogue is a bit like digital to analogue. olewill
 
VicMallows said:
The cheap, basic gennys (usually rated 750/850/900W) will at least be putting out a reasonable sinusoidal waveform. The frequency may not be spot-on but this is unlikely to worry most equipment (if you have a meter which can read frequency, simply adjust the speed on the governor to achieve 50Hz; the precise voltage is arguably of less concern for modern electronic equipment)

I would actually have more concerns about a poor quality inverter type genny driving a fussy switched-mode charger.
Click to expand...

You would think would be the case, but it's worth actually having a look with an oscilloscope. I found that the waveform on my Kipor (cheap, inverter type) was pretty close to sinusoidal whereas the waveform on an even cheaper Aldi conventional generator was significantly distorted.
 
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DaveS said:
You would think would be the case, but it's worth actually having a look with an oscilloscope. I found that the waveform on my Kipor (cheap, inverter type) was pretty close to sinusoidal whereas the waveform on an even cheaper Aldi conventional generator was significantly distorted.
Click to expand...

Interesting. What type of load (if any) were you applying in each case?
 
Back to practicalities. My 600watt cheepychinky happily runs a 25amp mastervolt supply and a wolf drill... It grunts in time with the drill operator but that's to be expected at my age.
 
William_H said:
It seems that in huge total power of a mains system these bites don't matter much.
Click to expand...

Historical trivia: In the early 1960s, Televisions often used half-wave rectification of the 240v AC mains to produce the high voltage DC supply for the valves. Because the chassis was directly connected to one side of the mains, it was preferred to connect it to the neutral (although the TV would work just as well with L/N reversed), so mostl TVs loaded the same half-cycle. This caused considerable problems for the supply company. Quite soon after, full-wave rectification became the norm .... maybe due to pressure exerted by the supply industry.
 
VicMallows said:
Historical trivia: In the early 1960s, Televisions often used half-wave rectification of the 240v AC mains to produce the high voltage DC supply for the valves. Because the chassis was directly connected to one side of the mains, it was preferred to connect it to the neutral (although the TV would work just as well with L/N reversed), so mostl TVs loaded the same half-cycle. This caused considerable problems for the supply company. Quite soon after, full-wave rectification became the norm .... maybe due to pressure exerted by the supply industry.
Click to expand...

Haven't heard that one before and not sure there were ever enough hot chassis TVs installed to affect the grid - however the huge number of switched mode supply devices in any large commercial environment did cause
waveform distortion locally, and I believe they spread/delayed the chop in devices in order to try and disperse the load over each cycle.
It was about that time that I understood the relevance of differentiation and integration in the school syllabus.....too late!
 
VicMallows said:
Historical trivia: In the early 1960s, Televisions often used half-wave rectification of the 240v AC mains to produce the high voltage DC supply for the valves. Because the chassis was directly connected to one side of the mains, it was preferred to connect it to the neutral (although the TV would work just as well with L/N reversed), so mostl TVs loaded the same half-cycle. This caused considerable problems for the supply company. Quite soon after, full-wave rectification became the norm .... maybe due to pressure exerted by the supply industry.
Click to expand...

They also used ceramic droppers for the valve heaters, not transformers, so they would run on DC 240v too-

I did try one on an army 'dynomotor' rotary converter, 12v to DC mains...

N
 
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