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Cost of keeping batteries charged?


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Bit of advice appreciated.

Can I work out the cost of shore power to run a smart charger at say 14p/KWhr?

That's for a "Genius" 7.2 amp charger connected to 2 x 110 Ahr batteries.

Generally batteries are well charged after cruising for a few days, so I guess its probably only a maintenance charge to consider.

However it would be on 24hr/day when boat is left unattended in marina, which is about 75% of the time!

Thanks in advance.

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7 minutes ago, Rebotco said:

Bit of advice appreciated.

Can I work out the cost of shore power to run a smart charger at say 14p/KWhr?

That's for a "Genius" 7.2 amp charger connected to 2 x 110 Ahr batteries.

Generally batteries are well charged after cruising for a few days, so I guess its probably only a maintenance charge to consider.

However it would be on 24hr/day when boat is left unattended in marina, which is about 75% of the time!

Thanks in advance.

 

 

W = A x V

Assuming 100% efficient charger will be using  W = 7 x 13

W = 90

 

1000 / 90 W = 11 hours for 14p

 

I reckon just over 1p per hour when running flat out at 7 amps, as the batteries become charged / fully charged and it drops to 2 or 3 amps, less than 0.5p per hour.

 

Say roughly £1 per week

 

You will need to keep an eye on the water levels in the batteries and check they are not getting hot.

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11 minutes ago, Rebotco said:

Bit of advice appreciated.

Can I work out the cost of shore power to run a smart charger at say 14p/KWhr?

That's for a "Genius" 7.2 amp charger connected to 2 x 110 Ahr batteries.

Generally batteries are well charged after cruising for a few days, so I guess its probably only a maintenance charge to consider.

However it would be on 24hr/day when boat is left unattended in marina, which is about 75% of the time!

Thanks in advance.

A lot depends on the efficiency of the charger....for instance my new model Victron Phoenix charger has a much lower no load draw than the Phoenix it replaced...mainly due to improved circuit design...no cooling fan....etc. Get a plug in current monitor from eBay etc and measure what it draws if I were you.

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42 minutes ago, Rebotco said:

Bit of advice appreciated.

Can I work out the cost of shore power to run a smart charger at say 14p/KWhr?

That's for a "Genius" 7.2 amp charger connected to 2 x 110 Ahr batteries.

Generally batteries are well charged after cruising for a few days, so I guess its probably only a maintenance charge to consider.

However it would be on 24hr/day when boat is left unattended in marina, which is about 75% of the time!

Thanks in advance.

 

Knowing nowt about your charger... 

We left the boat today with 4 fully charged 110Ah batteries on charge. The charger will therefore just be maintaining charge till we next visit next week. I'll try to remember to check how much the balance on the meter has gone down when we get there. I'd be very surprised if it's as much as 10p/day.

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13 minutes ago, George and Dragon said:

 

 

Knowing nowt about your charger... 

We left the boat today with 4 fully charged 110Ah batteries on charge. The charger will therefore just be maintaining charge till we next visit next week. I'll try to remember to check how much the balance on the meter has gone down when we get there. I'd be very surprised if it's as much as 10p/day.

 

That will probably give the most useful "real-world" result.

But I guess it will also depend on the size of the charger?

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2 minutes ago, Rebotco said:

But I guess it will also depend on the size of the charger?

I suppose so - the charger will supply the current needed to either bring up to fully charged or maintain at fully charged. Unless the charger can't actually manage to recharge your batteries then the difference between 90% and 96% efficiency may be all that matters. 

I have no idea what parameters are used to determine efficiency - efficiency at full load is likely to be very different from efficiency at 5% load.

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1 minute ago, George and Dragon said:

I have no idea what parameters are used to determine efficiency

 

 

Normally measured as PF (Power Factor)

 

A cheap, inneficient battery charger can have a PF as low as 0.6 (so only 60% of what goes in comes out), Quality chargers using electronic jiggery-pokery can have a PF of 1 so 100% of what goes in comes out.

 

The battery charger manufacturer should be able to tell you the Pf, but it is rarely quoted in sales documentation (unless it is very high)

 

Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). ... It is found by multiplying (kVA = V x A). The result is expressed as kVA units. PF expresses the ratio of true power used in a circuit to the apparent power delivered to the circuit.

 

 

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1 minute ago, Alan de Enfield said:

 

 

Normally measured as PF (Power Factor)

 

A cheap, inneficient battery charger can have a PF as low as 0.6 (so only 60% of what goes in comes out), Quality chargers using electronic jiggery-pokery can have a PF of 1 so 100% of what goes in comes out.

 

The battery charger manufacturer should be able to tell you the Pf, but it is rarely quoted in sales documentation (unless it is very high)

 

Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). ... It is found by multiplying (kVA = V x A). The result is expressed as kVA units. PF expresses the ratio of true power used in a circuit to the apparent power delivered to the circuit.

 

 

Will the pf not vary depending on the load? At full load pf might be quite good whereas at 10% load it could well be rubbish.

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If it's just to keep the batteries topped up wouldn't a small solar panel with an appropriate controller be sufficient?  That is what we used last winter when we could not get to the boat for about 4 months and it worked very well.  Personally I would be nervous about keeping a boat powered from the mains unattended for a long period.

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3 hours ago, NBDensie said:

If it's just to keep the batteries topped up wouldn't a small solar panel with an appropriate controller be sufficient?  That is what we used last winter when we could not get to the boat for about 4 months and it worked very well.  Personally I would be nervous about keeping a boat powered from the mains unattended for a long period.

 

Yes, that is what I have.

100W panel has worked well for over 3 years.

But more recently it has been getting less effective.  I suspect the aging batteries are becoming more sulphated now and require more oomph to keep charged up.

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On 10/05/2021 at 21:21, Alan de Enfield said:

 £1 per week

 

I  agree .

So it was a surprise to me that £15 was consumed in a week. Turned out this was a parting gift from the charger 

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  • 2 weeks later...
On 10/05/2021 at 21:54, George and Dragon said:

Knowing nowt about your charger... 

We left the boat today with 4 fully charged 110Ah batteries on charge. The charger will therefore just be maintaining charge till we next visit next week. I'll try to remember to check how much the balance on the meter has gone down when we get there. I'd be very surprised if it's as much as 10p/day.

And due to certain issues getting in the way we've only now got back to the boat... Balance on the meter has gone down by £1.28 which over 16 days very handily works out to exactly 8p/day.

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2 hours ago, George and Dragon said:

And due to certain issues getting in the way we've only now got back to the boat... Balance on the meter has gone down by £1.28 which over 16 days very handily works out to exactly 8p/day.

 

That is very helpful, thank you.

The real world cost is exactly what I was looking for, rather than mathematical theorising!

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On 10/05/2021 at 22:24, Alan de Enfield said:

 

 

Normally measured as PF (Power Factor)

 

A cheap, inneficient battery charger can have a PF as low as 0.6 (so only 60% of what goes in comes out), Quality chargers using electronic jiggery-pokery can have a PF of 1 so 100% of what goes in comes out.

 

The battery charger manufacturer should be able to tell you the Pf, but it is rarely quoted in sales documentation (unless it is very high)

 

Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). ... It is found by multiplying (kVA = V x A). The result is expressed as kVA units. PF expresses the ratio of true power used in a circuit to the apparent power delivered to the circuit.

 

 

I thought power factor was something complicated to do with current and voltage being out of phase in an AC system, such that VA is not the same as W.  Alan's quote seems to bear that out.

 

But it seems it may also be used to express efficiency - which is odd as we have err... efficiency as a good word for that.

 

Which is it?  Or both?

 

 

 

 

 

 

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1 hour ago, Tacet said:

I thought power factor was something complicated to do with current and voltage being out of phase in an AC system, such that VA is not the same as W.  Alan's quote seems to bear that out.

 

But it seems it may also be used to express efficiency - which is odd as we have err... efficiency as a good word for that.

 

Which is it?  Or both?

Alan is confused. Power factor is the ratio of power to VA. It is not directly related to efficiency of a charger, which mostly relates to how much waste heat is produced by eg regulating the output voltage linearly (as opposed to PWM /switch mode), resistance in transformer winding and electronic components, using ordinary silicon diodes etc etc. A charger with low power factor will use more current than one with a good power factor, and this current will create resistive heating, thus contributing to loss of efficiency, but this doesn’t matter in terms of running costs because the electricity meter measures only real power, not VA.

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12 minutes ago, nicknorman said:

Alan is confused. Power factor is the ratio of power to VA. It is not directly related to efficiency of a charger, which mostly relates to how much waste heat is produced by eg regulating the output voltage linearly (as opposed to PWM /switch mode), resistance in transformer winding and electronic components, using ordinary silicon diodes etc etc. A charger with low power factor will use more current than one with a good power factor, and this current will create resistive heating, thus contributing to loss of efficiency, but this doesn’t matter in terms of running costs because the electricity meter measures only real power, not VA.

 

So, how would you express or define a battey charger with a Pf of 0.6 compared to one with a Pf of 0.9

 

It was explained to me that it is a ratio (or percentage) comparing the power input against the power output, or in other words efficiency.

Is that not correct ?

 

I know the thread is about using a shoreline, but :

If we were using a charger from the small generator the Pf will determine what charger can be used, so for example a 60 amp charger with a Pf of 0.9 could be run off a 1000w generator, but the same generator could only run a 40amp charger with a Pf of 0.6

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You middle para is correct, but comparing input power to output power is nothing to do with power factor and/or VAr. Input VA is not “input power” it is “input VA”!

 

Ref para 3 yes it is about shore power. The thing with generators and inverters is that in nearly all cases the VA output rating is significantly higher than the W output rating, so within reason a non unity power factor can be tolerated without adverse effect. The other thing is that for something like a charger, the PF will vary with output load and whilst it might be quite far from unity at low outputs, it’s likely to be closer to unity at high outputs.

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Getting back to the original post, it has been shown that the cost of maintaining charge is next to minimal especially when it is factored into the battery life/cost equation, plus the advantage of fully charged batteries when you want to use the boat as consumption is likely to be high for the first few hours.

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6 hours ago, Ex Brummie said:

Getting back to the original post, it has been shown that the cost of maintaining charge is next to minimal especially when it is factored into the battery life/cost equation, plus the advantage of fully charged batteries when you want to use the boat as consumption is likely to be high for the first few hours.

That's it .

The cost  of not looking after the batteries is always going to be greater sum.

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