Electricary Calcs (1 Viewer)

Brakers

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Hi Fellow Frat Clubbers

As some of you might know I have a Autotrail Cheyenne 840D and in previous posts have been discussing various problems I though I had with my battery system. Anyway going on from that Techno commented on my wiring to my leisure batteries was to use his words Sh*t, and to be honnest I agree.

Apparently Autotrail in their infinite wisdom wired up the two leisure batteries with separate feeds of 4mm wire to each of the batteries.
I have connected the batteries together using 25mm multi-core cable.
I am going to have an 1800wat inverter fitted, also some other work done, I was hoping to upgrade the leads from my batteries to the EC325 to a more robust wire but have been told by Southdown motorhomes who will be carrying out the work this cannot be done because of the connections to the EC325. What a bummer.
Anyway my question is to all you techy people out there does anyone know what current can safely be put through these 4mm wires. I’ve tried to check on the internet but most sites refer to house electrics.

Many Thanks Tony
 

DBK

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You certainly won't run your 1800W inverter through such tiny wires. This page has a calculator which shows the losses through the wires. It suggests losses of around 2 or 3 percent are acceptable but the length of the cable is also a factor. For example a 4mm cable just 2m long is good for around 25 amps but if 4m long it is down to just around 12 amps. An 1800W inverter will need a minimum of 150 amps.

However, your inverter would be wired with its own leads to the battery, ideally through an isolating switch and be sited as close to the batteries as possible.

http://www.12voltplanet.co.uk/cable-sizing-selection.html
 
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Brakers

Brakers

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An 1800W inverter will need a minimum of 150 amps.
I don't expect to run the inverter to it's full capacity, 25amps will more than likely be over the top of what I want the inverter to run, am I correct in saying to run the inverter at it's full load then I would need wire to withstand 150amps, is that correct or am I way off?
Many Thanks Tony

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DBK

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I don't expect to run the inverter to it's full capacity, 25amps will more than likely be over the top of what I want the inverter to run, am I correct in saying to run the inverter at it's full load then I would need wire to withstand 150amps, is that correct or am I way off?
Many Thanks Tony
I edited my post while you were posting. The inverter should have its own wiring capable of coping with the maximum load and be protected by fuses. Anything less would be a fire risk.

I suggest finding someone who can install it correctly otherwise it could be dangerous given the currents involved and heat generated if something is wrong.
 
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Brakers

Brakers

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You certainly won't run your 1800W inverter through such tiny wires.
Is there a way round this, I'm no good with electrics so have to rely on other people. Can the inverter be wired straight from the batteries bypassing the EC325 with largher wires?
Many Thanks Tony
 
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Brakers

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Thats the trouble with typeing someone posts while you are typing

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Lenny HB

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This site has a lot of usefuf info and a volt drop calculator.
A 4mm cable for the main feed I would class as not fit for purpose, needs to be a at least 10mm sq.,
 
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Brakers

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I suggest finding someone who can install it correctly otherwise it could be dangerous given the currents involved and heat generated if something is wrong.
Yes your right, this is me getting things wrong again, Southdown Motorhomes said they will fit the inverter, I just asked them if the wireing to the batteries could be upgraded and they said as my previous post, they did not say they would wire the inverter through those wires, that was me assuming the power would have to go through those wires. I sure they will put a separate feed to the inverter. But I will ask the question.
Many Thanks Tony
 

DBK

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Is there a way round this, I'm no good with electrics so have to rely on other people. Can the inverter be wired straight from the batteries bypassing the EC325 with largher wires?
Many Thanks Tony
Yes. :) That's how it should be done - with fat boy wiring.

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Brakers

Brakers

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A 4mm cable for the main feed I would class as not fit for purpose, needs to be a at least 10mm sq.,
I don't think I understood what was going to be fitted, as DBK said the inverter will need to have it's own wireing and I'm sure Southdown will do that but as I said I will ask the question.
Many Thanks Tony
 
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Lenny HB

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Is there a way round this, I'm no good with electrics so have to rely on other people. Can the inverter be wired straight from the batteries bypassing the EC325 with largher wires?
Many Thanks Tony
That is the standard way of wiring an inverter, my 1000w inverter is wired direct to the batteries with 25mm sq., cable via a 100 amp fuse and a battery cut out switch.

Thats the trouble with typeing someone posts while you are typing
Yep always happens.:)
 

Lenny HB

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One more comment "Southdown", you must be well healed will cost you an arm and a leg.:D

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When I think of it the vehicle has full LED lighting except for the 240v mains lighting so I expect for what the 4mm wireing has to handle it would be adequate.
Many Thanks Tony
 
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Brakers

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One more comment "Southdown", you must be well healed will cost you an arm and a leg
Well I've got the arm but i'm not sure about the leg. LOL.
If I were fit enough, and confident I would do it myself.
Many Thanks Tony
 
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Brakers

Brakers

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Yes. :) That's how it should be done - with fat boy wiring.
Hi DBK am I correct in saying your the one who has an 1800T inverter fitted with a separate consumer unit fitted?
Many Thanks Tony

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DBK

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When I think of it the vehicle has full LED lighting except for the 240v mains lighting so I expect for what the 4mm wireing has to handle it would be adequate.
Many Thanks Tony
It will be fine for use as intended I think. The only time it will get a heavy load is if the batteries run down a bit and you start the engine, at which point the charging currents might be over twenty amps or thereabouts but probably not for long and the wires should be protected by suitable fuses in the worst case.
 

DBK

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Hi DBK am I correct in saying your the one who has an 1800T inverter fitted with a separate consumer unit fitted?
Many Thanks Tony
You've thrown me there, I guess it depends on the inverter model and how it is wired - probably best to consult an expert at this point as there are different ways of wiring in an inverter. The simplest just have sockets on you plug things into directly. Others make all the sockets in the MH live but doing that means you have to handle what happens when on EHU.
 
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Brakers

Brakers

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The simplest just have sockets on you plug things into directly. Others make all the sockets in the MH live but doing that means you have to handle what happens when on EHU.
Hi DBK Yes you are correct in saying about what happens when you are hooked up to the EHU that is why I'm haveing one that detects if the 240v is conntected and switches accordingly.
Many Thanks Tony

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Lenny HB

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When I think of it the vehicle has full LED lighting except for the 240v mains lighting so I expect for what the 4mm wireing has to handle it would be adequate.
Many Thanks Tony
Sorry don't agree, with lights on, Truma heating fan running full blast, turn on a tap water & pump draws a few more amps you will get quite a volt drop, depending how long the cable runs are.
 
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Brakers

Brakers

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Sorry don't agree, with lights on, Truma heating fan running full blast, turn on a tap water & pump draws a few more amps you will get quite a volt drop, depending how long the cable runs are.
I do understand what you mean, but I must assume the manufactures of this vehicle have done their calculations as there must be hundreds of these vehicles running round with the same wireing as me. I would like the wireing upgraded but Southdown said it can't be done. So I've got to rely on autotrail's calculations.
Many Thanks Tony
 

Lenny HB

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I do understand what you mean, but I must assume the manufactures of this vehicle have done their calculations as there must be hundreds of these vehicles running round with the same wireing as me. I would like the wireing upgraded but Southdown said it can't be done. So I've got to rely on autotrail's calculations.
Many Thanks Tony
Like most British manufacturers they build to price rather than quality, take a look at the wiring in a German van and you will see the difference.

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Jul 29, 2007
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I don't expect to run the inverter to it's full capacity, 25amps will more than likely be over the top of what I want the inverter to run, am I correct in saying to run the inverter at it's full load then I would need wire to withstand 150amps, is that correct or am I way off?
Many Thanks Tony

If your not going to run the inverter to its full capacity, why not get a smaller one? You must wire the inverter with cable that will allow it to run at its maximum output, anything else is a no no.

Ian
 
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Based on my experience and ownership of a similar AutoTrail the built in wiring is well able to run the systems on EHU (240v) and off (12v). Adding an inverter I assume you intend to run some mains (240V) equipment. Would you care to say what?
 
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Like most British manufacturers they build to price rather than quality, take a look at the wiring in a German van and you will see the difference.
Not in my Hymer you won't. I've never seen a MH or caravan wired to an acceptable standard after 40 years of owning them. The only one that came closed was a '90s Adria.

Edit: Maybe I should clarify: every van I've owned (with the exception of the Adria) has had inadequately sized wiring, no built in wiring runs (trunking / conduit) and not even a dedicated wiring harness. It all looks added as an afterthought. I've seen the bases of cupboards and lockers with unguarded wiring literally covering the floor, excess and unnecessary wiring taped up, wiring stretched taut to reach between terminations, no wiring run documentation available to dealers or owners, and plug terminations too small for the size of wire necessary. Most apply to most vans I've owned. They all apply to my 2005 Hymer.

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Dec 23, 2014
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Having moved from an AT to a Carthago I am very impressed with the wiring. If it is typical of German quality then it is miles ahead of UK standards.:Smile:
 
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Brakers

Brakers

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Would you care to say what?
Initially I only intend to run a Freesat PVR, a PS3, I would like to get one of those coffee pod makers which quite high in watage, I also would like later on to run an air conditioner but that is in the future I want to be ready I don't want to fit a smaller inverter then have to upgrade later on.
Many Thanks Tony
 
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Brakers

Brakers

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Like most British manufacturers they build to price rather than quality
I know you are correct in that statement, but apart from everyone buying German vehicles then we are stuck with it. Just out of interest I've not looked at German vehicles but are they equal to or dearer than other models for the same spec? not that I can afford to change this one. :-(
Many Thanks Tony

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Lenny HB

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Not in my Hymer you won't. I've never seen a MH or caravan wired to an acceptable standard after 40 years of owning them. The only one that came closed was a '90s Adria.

Edit: Maybe I should clarify: every van I've owned (with the exception of the Adria) has had inadequately sized wiring, no built in wiring runs (trunking / conduit) and not even a dedicated wiring harness. It all looks added as an afterthought. I've seen the bases of cupboards and lockers with unguarded wiring literally covering the floor, excess and unnecessary wiring taped up, wiring stretched taut to reach between terminations, no wiring run documentation available to dealers or owners, and plug terminations too small for the size of wire necessary. Most apply to most vans I've owned. They all apply to my 2005 Hymer.
Wiring in both my 2008 Hymer and my current 2014 Hymer wiring is good OK bundled up a bit under cupboards but in easy accessible trunking though lockers & cupboards always plenty of slack making mods easy. Good sized cables with multiple circuits no skimping to save a bit of copper.

Initially I only intend to run a Freesat PVR, a PS3, I would like to get one of those coffee pod makers which quite high in watage, I also would like later on to run an air conditioner but that is in the future I want to be ready I don't want to fit a smaller inverter then have to upgrade later on.
Many Thanks Tony
Coffee machine fine but forget about trying to run an aircon unit from batteries and an inverter - you won't have the payload for all those batteries you would need.:)

I know you are correct in that statement, but apart from everyone buying German vehicles then we are stuck with it. Just out of interest I've not looked at German vehicles but are they equal to or dearer than other models for the same spec? not that I can afford to change this one. :-(
Many Thanks Tony
Buy sensibly in Belgium or Germany and you will be surprised how cheap they are, I am on my second new Hymer and I can't afford UK prices.
 
Dec 23, 2014
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Initially I only intend to run a Freesat PVR, a PS3, I would like to get one of those coffee pod makers which quite high in watage, I also would like later on to run an air conditioner but that is in the future I want to be ready I don't want to fit a smaller inverter then have to upgrade later on.
Many Thanks Tony
@Brakers We have a Nexpresso coffee maker which takes next to nothing to run and the TV equipment all runs from the 12v when mains is not available. For what you have described a quite small inverter would be okay. As for running AC from an inverter you will be wrecking batteries on a daily basis.
 

DBK

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Initially I only intend to run a Freesat PVR, a PS3, I would like to get one of those coffee pod makers which quite high in watage, I also would like later on to run an air conditioner but that is in the future I want to be ready I don't want to fit a smaller inverter then have to upgrade later on.
Many Thanks Tony
As well as the air conditioning I fear you won't be able to run the PS3 for very long either. A quick Google suggests they take around 200W in normal use.

I'm not sure what to recommend other than buying a generator. A laptop will take a fraction of the power so that may be the way to go for gaming or videos.

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