Leads & Cables

[EdRedBird]

Changed my mind on where I want the batteries: Back of the van seems a better place and designing on a max bank of 4 , 1 or 2 either side.
This will mean longer cables... Is that a possible issue


What Gauge cable should be used ... I will be going for the 50Amp DC DC charger?

 

[Ivory55]

Fat cables, that’s my limited knowledge. Haha

 

[Otter Spotter]

Watch your weight 4 batteries is a lot, 2 with solar should be more than enough unless you plan on feeding back to the National grid

 

[Tombola]

Yes search Google for 12v voltage drop. Then work out the lengths of cables you need.
Also work out where your mppt will go. Closer to the batts is best

 

[pappajohn]

Use the calculator on this link.
the total amps needed depends on how much power you need at any one time.
Try 25amps.
Just work out the distance one way, not live and earth.
Your charger wires may also need uprating.

https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

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[EdRedBird]

Tombola (autorouter I expect your advice soon too )
Otter Spotter ; Transit RWD I was actually considdering extra weight in the back)

So the thicker the better ("she said") : https://www.12voltplanet.co.uk/voltage-drop-calculator.html
12 V with a 50Amp inverter

Tombola playing with that calculator those 4 (12W total ) led would require a 3mm2 cross section (over the length of my "boot"?
That seems awfully thick considdering the wiring for the current factory lights

This is beginning to do my head in
Would either or both of you try to explain (again)

I first started off with the idea if an inverter, now i come to realise i might not need one

My considderations are : Ease off access to the battery ... duration of juice out of battery without a sneaky start
As I am rear wheel drive I was thinking of adding the extra weight of batteries to the back... woth the option of adding an extra 2 batteries when needed

OCD dictates 1 or 2 on each side

I did find a 12v Coffeemaker... but it takes 8 minutes to make a cup of coffee...and that is simply not on so the inverter is still an option

So I am looking at 100Ah @C100 CCA: 750A

That mean i can light a 1 Watt light for 100 hours right ...well actually 50 -80

Now 4 LED lights -> 12 W to 4.5-6h

IF I hang in a 60W mini fridge freezer.. that thing on its own drains that battery in 1.5 hour... I would need 10 batteries to keep that yoke running overnight????? That cannot be right ...and a helluva drive to charge them the next day

And what is the impact of a dolce Gusto running of an inverter ... I presume/asume no load on the inverter means nothing is drawn.

Sorry if I am a pain in the ass

 

[EML]

Changed my mind on where I want the batteries: Back of the van seems a better place and designing on a max bank of 4 , 1 or 2 either side.
This will mean longer cables... Is that a possible issue


What Gauge cable should be used ... I will be going for the 50Amp DC DC charger?

Longer cables are always a problem, but -

• Which cables? Are these just the 12V cables from the charger to the batteries?
• Why does the charger-to-battery cable have to be 'long'? Can you just increase the length of the mains cable instead?
• Are you going to have an inverter? The cables from the battery to the inverter are critical
• Is 50A enough? I worked on 100A for mine. If you have an inverter, what power will it be?

If you're looking at how much current the cables can carry without burning the van down, you should start with a table like this one. Spoiler: probably 16 sq.mm, but your charger or inverter manual should tell you anyway, together with different values for different lengths of cables. It's difficult to buy cables this big, and crimping tools at this size are expensive (I paid my local chandler for 5m of 16 sq.mm cables with crimped terminals; I think it was about £60).

I had a quick look at pappajohn's link, but I can't make sense of it. It doesn't appear to give the right answer if the cable size is based solely on voltage drop, so it's also doing something else, or maybe it's just got it wrong. Besides, the answer it's giving is way too big to be practical.

 

[EdRedBird]

Seriously this is too long ago..
P = I * V right?

So back to the above
12W = I *12V -> I = 1 my 4 lamps draw 1 A -> 100H on a 100ah battery
The fridge
60W = 5 * 12 --- 5 Amp ...20 H

And I calculate my wire thickness accordingly from battery to device \

did the penny drop are am I making a complete fool of myself?

 

[Coop]

I recommend the Victron Toolkit app for cable sizing.

 

[Lenny HB]

So I am looking at 100Ah @C100 CCA: 750A

That's a starter battery you need to look at the capacity at the C 20 rate.

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[Figaro]

For coffee use a kettle on gas

 

[EdRedBird]

EML From battery to DC-DC to house battery,
That has to be long(er) as the distance from my front seat to back doors exceeds the distance from driver seat (where my main battery is) to passenger seat where I first planned my leisure batteries>

The inverter... If ...will be either placed close to the in house ford secondary "leisure" battery or the battery bank
I still want to be able to calculate it drain on the battery
I might skip the Dolce Gusto and go for an Italian stove top coffee maker .....
She can forget about a hairdryer ...its rear wheel drive she can stick the head out of the window while I spin)

 

[Tombola]

Running fridges/freezers from leads is a big ask with no solar or lithium (for charge rate). You can pretty much forget it.
it will pull anywhere between 8 and 14 ah when running. Of course they dont run ALL the time, I noticed 75ah per day (24 hours) when using mine on low.
It is never an exact science as all our needs and power usage is different.

You are talking Coffe machines, Hair driers and fridges.
Rough translation = Lithium, Solar AND b2b if staying off grid.

 

[autorouter]

So back to the above
12W = I *12V -> I = 1 my 4 lamps draw 1 A -> 100H on a 100ah battery
The fridge
60W = 5 * 12 --- 5 Amp ...20 H

And I calculate my wire thickness accordingly from battery to device \

did the penny drop are am I making a complete fool of myself?

Yes those figures are correct. The Ah figure quoted by the manufacturer is usually the '20 hour rate', C20. That's the capacity if discharged at a steady rate for 20 hours. For example a 100Ah C20 battery will supply 5A for 20 hours. and will then be completely flat.

If it's discharged faster, say at a steady rate so it's flat in 5 hours, it won't give you 20A for 5 hours as you might expect. If you want it to last 5 hours you'd have to reduce the amps from 20A to maybe 18A, so the C5 capacity would be 5 x 18 = 90Ah, not 100Ah.

Similarly the C100 capacity would be larger than 100Ah, maybe 120Ah. So it could supply 1.2A for 100 hours.

The C20 capacity is the one most manufacturers quote, for comparison purposes, but be careful, not all of them do.

And I calculate my wire thickness accordingly from battery to device \

First thing to say is, there's two considerations: safety and voltage drop. If you size the wires so that the voltage drop is 3% or less, then they will be well within any safety requirement limits. That's why the amps limit is not mentioned much.

It's common to keep the voltage drop in cables to 3% or less. Voltage drop decreases with thickness, and increases with length. So if the cables are longer, they need to be thicker too to have the same voltage drop. That's why it's recommended to keep the cables short, especially the very high power ones from the batteries to the inverter.