Invertor cable run?

[Sierra2]

I've noted that the location I would ideally like to install a 2.5k Invertor means an approx 4.2 meter cable run to the battery bank (12v).

 

 

I've not chosen the make or model yet but noted for comments on here that only a 2m cable run is recommended for most brands. Can I get around this with a thicker gauge cables or should I change the location to keep to the two meter rule?

 

Chaz

Edited October 14, 2014 by Sierra2

[nicknorman]

It's all about the resistance so if you double the length, you need to double the cable cross sectional area.

 

Which is fine from a theoretical point of view but you can run into trouble with the physical size of the cables and trying to connect them to things especially at the inverter end. Decide a connection plan before you commit yourself. I suppose some arrangement whereby you have thick or doubled cable for most of the run, then thinning to a smaller or single cable at the end to connect to the inverter. Messy though, and adding lots more connections each of which are a source of resistance.

Edited October 14, 2014 by nicknorman

[bottle]

This is from the Victron site for their multi plus, (inverter/charger) 3Kva

 

4.2 Connection of battery cables

In order to utilize the full capacity of the product, batteries with sufficient capacity and battery cables with sufficient cross section should
be used. See table.

12/3000/120 24/3000/70 48/3000/35

Recommended battery capacity (Ah) 400–1200 200–700 100–400

Recommended DC fuse 400A 300A 125A

Recommended cross section (mm2)
per + and - connection terminal

0 – 5 m 2x 50 mm2 2 50 mm2 2 35 mm2
5 – 10 m 2x 70 mm2 2x 50 mm2 2x 35 mm2

 

* ‘2x’ means two positive and two negative cables.

 

Remark: Internal resistance is the important factor when working with low capacity batteries. Please consult your supplier or the relevant
sections of our book “Energy Unlimited”, downloadable from our website.
Procedure
Proceed as follows to connect the battery cables:
Use an insulated box spanner in order to avoid shorting the battery.
Avoid shorting the battery cables.

 

 

So assuming your system is 12v dc you require 2X 50mm² (if the inverter/charger is 4.2m from the batteries) per negative and positive run a total of four cables.

[Alf Roberts]

This is from the Victron site for their multi plus, (inverter/charger) 3Kva

 

 

Avoid shorting the battery cables.

 

 

Useful bit of advice.

[Detling]

I can't see how you connect 2 positive and 2 negative into a Victron 12/3000/120 as mine only has one hole for positive and one hole for negative cable. Mine has I think 70mm welding cable run for about 3 meters to the battery bank, Remember also it is very unlikely in a canal boat to run anything over 1 KW for more than a few minutes, probably the largest current for a long time is the charger onto depleted batteries ie 100A+ for 30 mins or so before the batteries start limiting the current. Even the washing machine only heats for a few minutes the rest of the time it is just the motors.

[smileypete]

If putting it closer means a bigger risk of moisture or extreme damp or heat affecting it, I'd go for the longer run instead.

 

'Amps divided by three' is a good rule of thumb for sizing cable in mm, and will do up to 5 meters for most loads on a 12V boat, increase pro rata beyond that. For charging sources I'd consider halving the 5 meters to minimise voltage drop.

 

The above rule of thumb seems to agree with Victrons numbers. Not familiar with the Victron, but sometimes 2 terminals can go on a single stud 'back to back'.

 

cheers, Pete.

~smpt~

Edited October 14, 2014 by smileypete

[jonesthenuke]

I recently used some 70mm cable, the quoted resistance is 0.272 Ohms/km at 20C. For the suggested ~4 m run so an 8m long circuit, resistance will be 8*0.272/1000 =0.002176 Ohms (neglecting connection resistance which is independent of length anyway).

 

Current will be (say) 250A so volt drop is 0.544V, so it seems worth running double cables if you can. However note this is for peak loading.

 

Do you have space for the cables, including suitable bending radii?

[bottle]

I can't see how you connect 2 positive and 2 negative into a Victron 12/3000/120 as mine only has one hole for positive and one hole for negative cable. Mine has I think 70mm welding cable run for about 3 meters to the battery bank, Remember also it is very unlikely in a canal boat to run anything over 1 KW for more than a few minutes, probably the largest current for a long time is the charger onto depleted batteries ie 100A+ for 30 mins or so before the batteries start limiting the current. Even the washing machine only heats for a few minutes the rest of the time it is just the motors.

 

By hole, do you mean hole in the casing because the terminals in the Victron are 8mm studs.

 

Now I do not think that VIctron would recommend two cables if two cables would not fit.

 

They also may recommend two cables, as one (of suitable size) could be unwieldy to run and fit.

[Sierra2]

Thanks for the replies and information. She is a new fitout so have space/freedom to work with.

 

What I've aimed at doing is keeping all wiring as high up as possible and also to keep the DC wiring to the Port side and AC to Starboard. Sorry for the blurry panoramic photo.

 

To the left hand side of the photo in the recess with the cable trays will be the DC fuse board and battery charger next to that.

 

To the Right the consumer unit (already in place) and next to that where I wanted to fit the Inverter.

 

The battery bank (330aH, 12v) lives in the engine bay below the DC Fuse Board, hence a 4.2m cable run to the other side of the boat.

 

The inverter could be fitted in the engine bay, to the grey ply sheet just below the door into the Saloon with a 1.8-2m run. This isn't what I want ideally hence the cable question.

 

As I still need to buy a battery charger a combi unit could be an option but I was never a fan of 'eggs in the same basket'

In this case I assume fitting the unit next to the DC fuse board to be preferable for the short wiring run to the batts, but mixes up my plans to keep both sources separate

 

Chaz

 

 

 

[Paul C]

Thanks for the replies and information. She is a new fitout so have space/freedom to work with.

 

What I've aimed at doing is keeping all wiring as high up as possible and also to keep the DC wiring to the Port side and AC to Starboard. Sorry for the blurry panoramic photo.

 

To the left hand side of the photo in the recess with the cable trays will be the DC fuse board and battery charger next to that.

 

To the Right the consumer unit (already in place) and next to that where I wanted to fit the Inverter.

 

The battery bank (330aH, 12v) lives in the engine bay below the DC Fuse Board, hence a 4.2m cable run to the other side of the boat.

 

The inverter could be fitted in the engine bay, to the grey ply sheet just below the door into the Saloon with a 1.8-2m run. This isn't what I want ideally hence the cable question.

 

As I still need to buy a battery charger a combi unit could be an option but I was never a fan of 'eggs in the same basket'

In this case I assume fitting the unit next to the DC fuse board to be preferable for the short wiring run to the batts, but mixes up my plans to keep both sources separate

 

Chaz

 

 

 

 

Rearrange the stuff to fit the inverter the same side as the battery bank, its more important that the 12V DC cable run is short, than the 230V AC run (to the consumer unit). Is there a strong reason why the 12V DC panel and the 230V AC consumer unit need to be on different sides of the boat? On ours, I got all the electrics into a cupboard; and because its mounted neatly on the back wall of the cupboard (which is hinged to allow good access to the wiring) the cupboard is still usable.

Edited October 16, 2014 by Paul C

[Bod]

Remember the "Distance" is the length of cable needed, not the straight line "as the crow flys".

If the cable has to go under/around/over, its length may be far greater, than expected.

 

Bod

[nicknorman]

If you are contemplating a reasonable size inverter as per your OP, I would say 330AH is not enough. Surely you can make room for at least 440AH at this stage?

[smileypete]

If the inverter/combi is going against a steel hull or bulkhead I'd try and space it off at least a couple of inches, keep the condensation risk to a minimum. Also put a dripshield above it to protect from condensation coming from above.

 

cheers, Pete.

~smpt~

[Keeping Up]

Remember also it is very unlikely in a canal boat to run anything over 1 KW for more than a few minutes, probably the largest current for a long time is the charger onto depleted batteries ie 100A+ for 30 mins or so before the batteries start limiting the current. Even the washing machine only heats for a few minutes the rest of the time it is just the motors.

 

If you are doing jacket potatoes in a microwave you could be running nearly 1.5 kW for over 15 minutes.

[by'eck]

 

If you are doing jacket potatoes in a microwave you could be running nearly 1.5 kW for over 15 minutes.

 

Wow you must like humungous ones. A single good sized spud takes around 7 minutes with 850 watt microwave drawing 110 amps. Mind you I do bung it next to the steak and mushrooms under the grill for a while to get that authentic baked effect

[Justme]

Our Victron 12v 3kVa is wired in using 120mm2 csa cable. It fits the cutouts no problem.

 

Yes it does need more effort to run the cable but its not that difficult if you can design it in from the start.

 

If I remember right the quoted cable sizes for the Victrons are for the round trip distance not just one way.

[Keeping Up]

 

Wow you must like humungous ones. A single good sized spud takes around 7 minutes with 850 watt microwave drawing 110 amps. Mind you I do bung it next to the steak and mushrooms under the grill for a while to get that authentic baked effect

I do like humungous, and so does Pingu so there are usually two of them in there.

[by'eck]

I do like humungous, and so does Pingu so there are usually two of them in there.

 

Yes realised that later. I was surprised how little current mine drew though. Was lead to believe that its close to twice the power rating of the microwave but that would give a draw around 140 amps plus inverter inefficiencies, say 145 amps.

[nicknorman]

Yes realised that later. I was surprised how little current mine drew though. Was lead to believe that its close to twice the power rating of the microwave but that would give a draw around 140 amps plus inverter inefficiencies, say 145 amps.

Obviously the energy has to go somewhere - the microwave output is obvious, but if it took the same again as inefficiency losses, well 850w is quite a lot and it would get very hot! But fortunately it doesn't!

[by'eck]

Obviously the energy has to go somewhere - the microwave output is obvious, but if it took the same again as inefficiency losses, well 850w is quite a lot and it would get very hot! But fortunately it doesn't!

 

Is a microwave oven loaded by the total water content of food within though? Must admit I've never checked. If not where does all the energy go if you run one empty.

[Paul C]

 

Is a microwave oven loaded by the total water content of food within though? Must admit I've never checked. If not where does all the energy go if you run one empty.

 

Don't run a microwave while its empty! The vast majority of the microwaves go into the food, more accurately they are targeted to heat up the water (and all food contains water in some proportion). I dare say some is lost but it won't be much.

[Richard10002]

There are loads of cable calculators on line. I think my cable run is about 26ft there and back. I've got 95mm2 cable for a 2500W inverter charger. Dont forget the megafuse aswell.

[nicknorman]

Is a microwave oven loaded by the total water content of food within though? Must admit I've never checked. If not where does all the energy go if you run one empty.

No, it produces a fixed output which is why you need to heat 2 tatties for longer than if you only put 1 in. If you put nothing in, there will likely be all sorts of arcing as very high electric fields are generated and you may damage the thing.

[Keeping Up]

I think the total time you need to run it for, is proportional to the square root of the quantity of food. This means that if you put two spuds in you need to run it for 1.414 times as long as if you had only one spud in there, or 1.732 times as long for 3 spuds etc. To keep it simple for Pingu I just tell her to do it for half as long again when there are two spuds in there; the same formula applies to other food items too :-)

[nicknorman]

I think the total time you need to run it for, is proportional to the square root of the quantity of food. This means that if you put two spuds in you need to run it for 1.414 times as long as if you had only one spud in there, or 1.732 times as long for 3 spuds etc. To keep it simple for Pingu I just tell her to do it for half as long again when there are two spuds in there; the same formula applies to other food items too :-)

I think the same total energy will go in, so if you double the mass you would have to double the time to get the same energy, HOWEVER the microwaves don't actually penetrate that far, so for something like a tattie the middle is cooked by conduction, not directly by microwave. Meantime the outside is overcooking and the microwaves energy is going into boiling off water at or near the surface. So when you add another tattie you don't need to double the time / energy because less is wasted in converting liquid water to vapour, meanwhile it still takes not far off the same time for the heat to permeate to the middle.

Edited October 17, 2014 by nicknorman