/ Energy usage question.

This topic has been archived, and won't accept reply postings.
Dax H - on 05 Jan 2017

I was musing with a guy on site today about charging things in the van or car over plugging it to a mains socket.

I use a 4 gas detector on some sites and stick it on charge from the 12v socket in my van for the drive home and leave it on charge over night.

My question to the hive brain of UKC is this.
Is it more energy efficient to charge it from the mains at home or to charge it from my van battery.

I assume that electricity generated via the national grid is probably more efficient than my van engine burning a little extra fuel but how much extra fuel will the van use on the drive home to charge the detector and top up the battery in the morning.

Balancing that out though the mains charger is a transformer that runs very warm (waste heat) whilst the van charger stays flat cold.

I suspect the difference will be tiny but if anyone knows the answer it would be interesting to know.

Edited to add, the reason for the musing was because the guy I was working with has a work issued tough book and his van charger was broken so until his company replaces it he is in capable of working alone because every job has to be booked on to the system and he refuses to charge his tough book at home because they won't reimburse the electric costs.
Post edited at 19:35
marsbar - on 05 Jan 2017
In reply to Dax H:

The first I don't know, the second scenario sound very inefficient though . Is he just an awkward sort, or have his workplace really really annoyed him? I blame HR.
Lusk - on 05 Jan 2017
In reply to Dax H:

> Edited to add, the reason for the musing was because the guy I was working with has a work issued tough book and his van charger was broken so until his company replaces it he is in capable of working alone because every job has to be booked on to the system and he refuses to charge his tough book at home because they won't reimburse the electric costs.

Speechless! Tell him I'll send him 16p to cover his electric.
Dax H - on 05 Jan 2017
In reply to marsbar:

Awkward sort, 100% jobsworth.
The company has the most toothless HR dept ever and most of the guys are in a decent union hence they get away with things like this.

Someone must know the answer to the question though,
krikoman - on 06 Jan 2017
In reply to Dax H:

Charging in the van would be the most efficient, the van probably produces more electricity than it needs, to charge the battery and to overcome friction of the engine. It might also depend on what voltage the detector charges at too, charger losses.

16p is probably overestimating the cost by quite a bit to be honest, too.
3
GrahamD - on 06 Jan 2017
In reply to krikoman:

> Charging in the van would be the most efficient, the van probably produces more electricity than it needs, to charge the battery and to overcome friction of the engine. It might also depend on what voltage the detector charges at too, charger losses.

That isn't how a regulator works. The van produces exactly the amount of electricity it needs all the time. If you take more electricity the generator will put more load on the engine.

As to what is more efficient its probably in the noise. Modern mains chargers shouldn't be getting significantly warm, though.
krikoman - on 06 Jan 2017
In reply to GrahamD:

> That isn't how a regulator works. The van produces exactly the amount of electricity it needs all the time. If you take more electricity the generator will put more load on the engine.

Agree, but the extra loading of the charger will be negligible considering the losses within the system.

> As to what is more efficient its probably in the noise. Modern mains chargers shouldn't be getting significantly warm, though.

Any heat is lost energy though.

Ideally world the energy cost would be the same, as the detector would only need to take what it needs to be charged. In terms of pounds and pence (pence really) this would probably mean that plugging into the mains would work out cheaper, as electricity is cheaper then petrol per kW. Either way it would be very difficult to give a definitive answer as there are too many variables.

Suffice to say it won't be costing much and the bloke's being an arse.

1
deepsoup - on 06 Jan 2017
In reply to krikoman:
> Any heat is lost energy though.

I vaguely remember a discussion about energy saving light bulbs on here a while back that went around this a few times. It's winter, and most of us are heating our homes at the moment - so heat produced inside the home isn't 'lost' energy any more than the heating is! Although, joule for joule, electricity is a fair bit more expensive than gas obviously.

(The argument was more pertinent to light bulbs, because you tend to have the light on in any given room at the same time you're heating that room.)

> Suffice to say it won't be costing much and the bloke's being an arse.

I occasionally work with someone a bit like that, and it baffles me. It just seems like a recipe for making yourself utterly miserable. He doesn't seem to be miserable, but dear god he can certainly suck a lot of the joy out of my day. (I really enjoy my work most of the time - when I'm not working with people making it their mission to be a complete arse.)
Post edited at 10:46
GrahamD - on 06 Jan 2017
In reply to krikoman:

I agree, the low cost is subject to so many variables that it is impossible to call which is cheapest.

Whether the bloke is being an arse or not depends on whether this is symptomatic of a more general employer not providing tools for the job behaviour. It might just be the straw that broke the camels back. Or he might just be an arse.
duchessofmalfi - on 06 Jan 2017
There are too many unknowns and the question is too vague to answer properly but the question was:

Is it more energy efficient to charge at home or from the van?

It is fairly safe to assume the energy going into the battery is the same so the question becomes:

Which system uses more energy to charge? - this is complicated because it depends where you measure it.

If you measure the energy input at the plug (mains plug or 12v socket) then it just depends on the efficiency of the charger - there is no way of knowing this here so the only answer is "we don't know, requires further investigation". The fact one charger gets hotter is largely irrelevant: it does indicate energy loss but there are more variables at play - for instance if the wall charger gets 5C hotter while charging but charges in 10 minutes and the car charger gets hotter by only 1C but takes 10 hours then the cooler charger probably wastes more heat.

If you measure the energy input higher up - say at the power station or at the fuel pump then the car is likely to be less efficient over all that the power station (plus transmission) so for equal efficiency chargers home wins. If factor in renewables (eg wind) you are really recycling lost energy so the efficiency is arguably higher.

If you are really concerned about efficiency as "how much does it cost" then home is almost certainly more "efficient" being as the power station is efficient and you aren't paying duty on the fuel. However, the cost is so marginal that the convenience of charging wherever is handy certainly runs the argument.


Dax H - on 06 Jan 2017
In reply to duchessofmalfi:

I had not thought about fuel duty.
From flat it takes 6 hours to charge regardless of van or house.
In the real world the cost difference is probable less than £1 per year, I was just interested.

On to the work guy, the company is great and provides everything they need but for whatever reason it was going to take a week to get a new charger. Any right minded person would just charge it at home for the week.
wintertree - on 06 Jan 2017
In reply to Dax H:

This depends on the age of the car.

Something modern allows the battery to deplete in normal driving and recharges it with "free"or "waste" energy during breaking by raising the output of the alternator - effectively regenerative braking or KERS. In this case it is more efficient than charging from the grid as waste energy is used.

An older car with a fixed voltage alternator will be less efficient than the grid as engine output is raised to provide the increased alternator output, and an ICE is less efficient that the least efficient grid sources, let alone the gas and nuclear/wind/solar sources. (Using efficiency very loosely, mainly as a proxy for pollution and CO2 released.) Various studies on EV efficiency with a mixed generation have validated this although it's continually ignored by some quarters.

I am in my analysis assuming chargers from mains and car have equal efficiency. This is not guaranteed. With a modern alternator car charger efficiency is irrelevant as it's running of free/waste energy. In an old car it could sway the argument either way...

You may find this guide on smart alternators helps explain things - http://www.12voltplanet.co.uk/auxiliary-battery-charging-in-vehicles-with-smart-alternators.html
Post edited at 12:43
Timmd on 06 Jan 2017
In reply to Dax H:
> I had not thought about fuel duty.
> From flat it takes 6 hours to charge regardless of van or house.
> In the real world the cost difference is probable less than £1 per year, I was just interested.
> On to the work guy, the company is great and provides everything they need but for whatever reason it was going to take a week to get a new charger. Any right minded person would just charge it at home for the week.

You were tactful if you didn't gently ask him if the cost of charging it for a week wasn't less than any hassle caused by him not charging it at home in the grand scheme of things.
Post edited at 14:07
krikoman - on 06 Jan 2017
In reply to Dax H:

As an example, I have a charger which we use for charging phones and tablets.
The tablet is plugged in when we're not using it, my phone when it's needed, twice a week maybe less.
I also charge a couple of work instruments through it, but don't think any of those have been plugged in during this time period.
The charger is plugged into a "smart" energy motoring socket.

Over the last 26 days, we've used 0.57kWh of electricity this will have cost us 6p.
jkarran - on 06 Jan 2017
In reply to Dax H:

Charging a toughbook assuming that is some sort of tablet probably requires in the region of 0.1KWh assuming it is big and power hungry and totally flat after a day at work. That's about 1.2p/day. Your mate might have a point!

Against in car charging: Refining and road fuel is inefficient. Car engines are quite inefficient by comparison with grid scale heat engines, car alternators are quite inefficient by comparison with grid scale alternators.
For: DC-DC conversion tends to be quite efficient

Against charging at home: Power transmission is lossy but barely. The rectifier in the charger is lossy but after that it's a DC-DC converter like in the car, if it runs hot it's a piece of crap. Obviously driving any distance specially to plug something in to charge is likely to be self defeating but that doesn't seem to be your question.
For: Grid scale heat engines making electricity are efficient. It's winter, your charger is warming the house, probably to the tune of about 10-15W but assuming you have thermostatic oil/gas heating that heat goes some way to offsetting the losses from poor charger design.

My guess is the car charger requires maybe 20 to 50% more energy to be extracted from the ground than doing it at home.
jk
marsbar - on 06 Jan 2017
In reply to jkarran:

I must admit if I was his boss I'd agree to pay, and make the him fill in a very long boring form to do so.
Mark Edwards - on 06 Jan 2017
In reply to Dax H:

The way I see it is that the losses in charging it in the car are insignificant considering how much energy is lost via heat and friction when driving (unless the charge requirement are significant – which for a portable device, I doubt).
As opposed to the electricity grid where 10-20% losses are the norm.
Timmd on 06 Jan 2017
In reply to Mark Edwards:

That's my thoughts too.
Dax H - on 06 Jan 2017
In reply to jkarran:

A tough book is a small laptop made by Panasonic, it's a bit rugged and has a touch screen as well as a keyboard and designed for site use.

sebastian dangerfield on 06 Jan 2017
In reply to jkarran:



> Against charging at home: Power transmission is lossy but barely.

Depends where you live - average T losses is about 2-3%, but higher if you live in the south - and you need to take distribution losses into account to which are higher. Pushing 10% for most domestic customers.
Jim C - on 07 Jan 2017
In reply to marsbar:

> I must admit if I was his boss I'd agree to pay, and make the him fill in a very long boring form to do so.

Which he would certainly do in the companies time ( and very slowly, costing the company even more)
marsbar - on 07 Jan 2017
In reply to Jim C:

True. But if I've read it right he's costing them an additional member of staff at the moment.
Dax H - on 07 Jan 2017
In reply to marsbar:

> True. But if I've read it right he's costing them an additional member of staff at the moment.

Yes you read that right, we'll for about half a day per day.
Because he refuses to charge it at home he has to go to the nearest depot in the morning and plug in there to charge.
It's the sort of ridiculous situation that you would only come across in a public company (or in this case a public that was sold to private but is still run like a public company)
1
deepsoup - on 07 Jan 2017
In reply to Dax H:
> It's the sort of ridiculous situation that you would only come across in a public company (or in this case a public that was sold to private but is still run like a public company)

It really isn't you know. There is absolutely no shortage of dickheads in the private sector.
Timmd on 08 Jan 2017
In reply to Dax H:
What deepsoup said.

It can sometimes seem that how people see public and private sector people or companies, can be similar to how people will have specific political points of view, when the world is full of shades of grey.

I think it can lead to a certain lack of objectivity when talking about the nationalisation (or not) of things everybody uses like energy or water.

That an old lady watching her pension can pay more for her gas than somebody younger and working who is more internet savvy is deeply unjust, but some people are sure about how streamlined and efficient the private sector is, and that it should be applied to everything to make improvements.

Pardon my going off on a tangent...
Post edited at 14:33
marsbar - on 08 Jan 2017
In reply to Dax H:

Can't you make him go to the depot at the end of every day, leaving it on charge overnight and then him fetch it in the morning?
marsbar - on 08 Jan 2017
In reply to deepsoup:

It's probably easier in the private sector to take 20p for electricity from petty cash and tell him to f.ing well get on with it. Councils have complicated policies about stuff like that.
Timmd on 08 Jan 2017
In reply to marsbar:

That's true.
The New NickB - on 08 Jan 2017
In reply to marsbar:

> I must admit if I was his boss I'd agree to pay, and make the him fill in a very long boring form to do so.

I'd just give him 10p, the 30 seconds of his and my time resolving the matter would be more than enough wastage of resources.
ads.ukclimbing.com
Dax H - on 08 Jan 2017
In reply to deepsoup:

> It really isn't you know. There is absolutely no shortage of dickheads in the private sector.

You are correct but from my experience of my customers the public and ex public ones tend to have a far greater selection of jobs worths and muppets than those that have never been in public ownership.

They also tend to have far more management in place, currently my biggest customer has more management, schedulers and coordinators than they have operational staff to manage, schedule and coordinate.

It isn't just public though.
A mate of mine was a security guard for asda for a while, Asda brought a consultant in to look for savings and it was found that there were 3 managers looking after 3 security guards.

This topic has been archived, and won't accept reply postings.