# Anyone for an EHU Protector?



## Patrick_Phillips (Aug 17, 2006)

You arrive on site and they unlock a cupboard and plug your cable in - then lock it up again.
Now I worry. What happens if I blow the fuse in the cupboard? Will I wait until morning for leccy or will I inadvertently get some poor soul out of a nice warm bed?

I have long thought that I need a black box that sits on my end of the wire which I can set to the number of amps I can have - less one!
Of course I can't find a variable MCB.
I can only find MCBs of the same rating as the ones the site uses.

So I am thinking of building one!

Now here is the plan...
Can any nice electricians on here tell me if this is a good plan? Will I set fire to my van this way?
The cost of self build looks to be about £25 so, for me, worthwhile.

Patrick


----------



## p-c (Oct 27, 2007)

Watching with hopeful interest.
p-c


----------



## Techno100 (May 8, 2010)

Interesting but surely its easier to just not plug ALL your stuff in together :roll:


----------



## Patrick_Phillips (Aug 17, 2006)

Techno100 said:


> Interesting but surely its easier to just not plug ALL your stuff in together :roll:


Quite but how much can you use? It is easy enough to work out what you can use at the get-go when you have, say a 6 amp EHU. But will you remember over a week on site to rework your figures every time you plug something in?

You could use an ammeter. We have one. But again, you land up spending more time with the calculator than sunbathing. All I want is peace of mind and protection against getting it wrong...

Patrick


----------



## Techno100 (May 8, 2010)

Well the fridge is the priority and the kettle occasionally but we don't have electric heating so perhaps we're not as vulnerable.
Everything else is off my batteries.
I only had a loss of power on a CC&C site but my autochangeover relay hid the fact that it had happened but we noticed loads of folk trolling around outside with torches :lol:


----------



## cabby (May 14, 2005)

If that is what you think you need then have it by all means.
But unless the supply is really that low and you use a lot of 230v equipment I really do not see the point.

cabby


----------



## tonyt (May 25, 2005)

A set of skeleton keys might be an alternative


----------



## Glandwr (Jun 12, 2006)

We have a 3 position switch that reads 500w, 1000w and 2000w. Not sure if it is total consumption or just the heating. Useful though when on a mean EHU

Dick


----------



## Christine600 (Jan 20, 2011)

My van has a setting for this on the control panel over the door. It goes as low as 4 amps. I think it might be a function of the inverter. And that if I use more than ie 4 amps for a short period the inverter will supply the extra.

I guess the name of the inverter would be in the thick MH manual somewhere - if someone wants me to look it up.


----------



## Patrick_Phillips (Aug 17, 2006)

Christine600 said:


> My van has a setting for this on the control panel over the door. It goes as low as 4 amps. I think it might be a function of the inverter. And that if I use more than ie 4 amps for a short period the inverter will supply the extra.
> 
> I guess the name of the inverter would be in the thick MH manual somewhere - if someone wants me to look it up.


That would be interesting but I wouldn't want to condemn you to hours of searching...
I just so happens that I need to buy a new inverter!

Patrick


----------



## coppo (May 27, 2009)

Glandwr said:


> We have a 3 position switch that reads 500w, 1000w and 2000w. Not sure if it is total consumption or just the heating. Useful though when on a mean EHU
> 
> Dick


If its the same as ours its just for the heating.

Paul.


----------



## Grizzly (May 9, 2005)

An interesting idea though, as an interim measure, you might do as we do and make a brightly coloured luggage label that hangs on the kettle switch when we are on a low amperage site. It reads "HEATING ON" and reminds us that we can't have both space or water heating and the kettle. 

Touch wood it has worked on all but a couple of occasions and, as we also carry a set of keys for electricity boxes, they were soon sorted.


G


----------



## Christine600 (Jan 20, 2011)

Patrick_Phillips said:


> That would be interesting but I wouldn't want to condemn you to hours of searching...
> I just so happens that I need to buy a new inverter!


It's a Mastervolt Mass Combi 1200/60.

Mastervolt

It did not take me long.


----------



## coppo (May 27, 2009)

Christine600 said:


> Patrick_Phillips said:
> 
> 
> > That would be interesting but I wouldn't want to condemn you to hours of searching...
> ...


Good idea Christine but could you not flatten the hab batteries especially if the inverter was working for quite a while and you were unaware.

Paul.


----------



## listerdiesel (Aug 3, 2012)

It wouldn't be too difficult to fit a current transformer and monitor the output, feeding a comparator circuit which would look at a preset value and alarm if you got close, or you could have on one of the bar-graph LED arrays to show where you were on consumption, but at the end of the day the human operator is the most effective monitor available.

Like many others, we only have the microwave that needs AC power, and only 800W then. All the rest of our requirements like hot water, cooking and fridge are gas.

There are enough electronics and gadgets already, some necessary and some quite frivolous, let's not add too many more.

Peter


----------



## Patrick_Phillips (Aug 17, 2006)

listerdiesel said:


> It wouldn't be too difficult to fit a current transformer and monitor the output, feeding a comparator circuit which would look at a preset value and alarm if you got close, or you could have on one of the bar-graph LED arrays to show where you were on consumption, but at the end of the day the human operator is the most effective monitor available.
> 
> Like many others, we only have the microwave that needs AC power, and only 800W then. All the rest of our requirements like hot water, cooking and fridge are gas.
> 
> ...


I was trying to keep the design simple and cheap. Partly because if people wanted the facility, it would be expensive to have it made and sold as a product (CE marks etc). If it can be a simple "practical electronics" DIY design it would be better.

My interest is that I don't want to have to monitor everything all the time. I am looking for the carefree life!
More "what can I loose while I boil the kettle?" than "will the kettle take out the locked EHU?"

I am not doing so well here in my ambition to get comments on the circuit rather than why should anyone want the circuit!

And, worse, I have another electronic gadget to try and find/design - Something that will switch me to EHU automatically when the leisure batteries are getting low. I want to maximise the use of solar whilst still having the standby of EHU.

Maybe that is a step too far?

Patrick


----------



## pippin (Nov 15, 2007)

The simple answer? 

Replace the breaker in the MH "consumer unit" with a 6A one.

Or more accurately, feed all the individual breakers through a 6A one before the main ON/OFF breaker or trip.

It would not be too difficult to have a 10A breaker as well and just switch between the two depending upon how many amps you think the EHU will provide.


----------



## bigtwin (May 24, 2008)

pippin said:


> The simple answer?
> 
> Replace the breaker in the MH "consumer unit" with a 6A one.
> 
> ...


Discrimination?


----------



## Patrick_Phillips (Aug 17, 2006)

pippin said:


> The simple answer?
> 
> Replace the breaker in the MH "consumer unit" with a 6A one.
> 
> ...


Simple, yes, but not an answer...
If you put a 6a breaker in series with a 6a breaker which will trip first? Maybe not yours...

If you put a 6a in series with a 10a EHU, your 6a will definetly trip first but you will never get the full 10a you paid for...

My circuit would never lose you more than 1.25 amps (& at 6a only 1 amp).
Also bear in mind that there are EHUs out there at 2, 3, 4, 6, 10, 15 and 16. That is quite an investment in MCBs. That is why I suggest resettable fuses at 62 pence each!

Patrick


----------



## Techno100 (May 8, 2010)

Just do it Patrick!
I look forwards to your progress


----------



## Christine600 (Jan 20, 2011)

coppo said:


> Good idea Christine but could you not flatten the hab batteries especially if the inverter was working for quite a while and you were unaware.
> 
> Paul.


Yes it is possible. At a 4 amp site I had left the Alde heater setting on both gas and EHU. So it used more than 4 amps when heating the hot water tank. Took me a while to understand where the power went. Didn't flatten the battery though. And after setting the Alde to gas only it started charging again.


----------



## listerdiesel (Aug 3, 2012)

Limiting power by means of different MCB's is a bit of a scattergun solution, you're never sure if it is going to be accurate for what you need, and as has been mentioned, discrimination is going to be an issue.

We have 3 X 6A MCB's in the trailer for all our 230V services, it means that I cannot use our house Henry vacuum cleaner on high power as the breaker trips as soon as I start it up, so that works OK. Power drills are OK as long as they have variable speed.

The type of MCB also makes a difference. If I use 'A' rating, that is the fastest tripping of the range, but if I use a 'D' rating, that is the slowest tripping and used for magnetic loads with high starting currents.

Going back to the OP's original problem, maybe limiting power by MCB could be an answer, but there is still nothing stopping a combination of devices being switched on that collectively would exceed the supply rating.

Peter


----------

