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Here's a Very Nice Cable Calculator

Biggles

By Biggles
in Boat Building & Maintenance

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blackrose Veteran II

blackrose

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Posted (edited)

I'm not sure that I understand how to use it? What's the maximum voltage drop we should be looking for? 0.3v or thereabouts?

 

Also if you click on the cross-sectional cable area, does it allow you to work backwards to determine the maximum cable length or maximum DC current?

 

And what's the inverter calculator thing underneath all about? It's seems fine if you just leave things on a constant power draw, but I imagine most of us switch things on and off, making the calculator a bit simplistic. I'll just use my battery monitors.

Edited by blackrose
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WotEver Veteran II

WotEverDonate to Canal World

Posted
Posted

I'm not sure that I understand how to use it? What's the maximum voltage drop we should be looking for? 0.3v or thereabouts?

Your call - it depends on what's being fed. A phone charger won't mind being fed around 10V, but many fridges get upset with anything below say 12.2V

 

Also if you click on the cross-sectional cable area, does it allow you to work backwards to determine the maximum cable length or maximum DC current?

No, it shows you what voltage would be available at the load. Basically it simply deducts the voltage drop from a nominal 12V. The load and cable length are both fixed elements in most installations (eg a TV drawing 3A with a total cable run of 40 metres), so this calculator shows you what cables are suitable, and what the drop will be down them at that run with that current being drawn.

 

And what's the inverter calculator thing underneath all about?

It gives you a guide as to how many batteries and what size will be required to supply a certain draw from a 'typical' inverter with 88% efficiency, and how long they will be able to supply that power. So for instance if you have a 2kW washing machine and you have 6 x 99Ah batteries, you'll be able to do a 2 hour wash before having to completely recharge your bank. I can see it being a really useful tool for opening folks' eyes as to how knackering high-demand appliances can be in the real world.

 

Tony

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blackrose Veteran II

blackrose

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Posted

Your call - it depends on what's being fed. A phone charger won't mind being fed around 10V, but many fridges get upset with anything below say 12.2V

 

 

No, it shows you what voltage would be available at the load. Basically it simply deducts the voltage drop from a nominal 12V. The load and cable length are both fixed elements in most installations (eg a TV drawing 3A with a total cable run of 40 metres), so this calculator shows you what cables are suitable, and what the drop will be down them at that run with that current being drawn.

 

 

It gives you a guide as to how many batteries and what size will be required to supply a certain draw from a 'typical' inverter with 88% efficiency, and how long they will be able to supply that power. So for instance if you have a 2kW washing machine and you have 6 x 99Ah batteries, you'll be able to do a 2 hour wash before having to completely recharge your bank. I can see it being a really useful tool for opening folks' eyes as to how knackering high-demand appliances can be in the real world.

 

Tony

 

Thanks. Should this calculator be "pinned" for future reference by forum members?

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blackrose Veteran II

blackrose

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Posted (edited)

Those links now seem defunct (apart from Tony's tables), so here's another cable size calculator.

 

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

I'm going to replace a 12v circulation pump (2amp fuse) with a bigger 12v pump which takes a 15 amp fuse. I don't want to replace the 8m of 4mm2 wiring to the switch, so I was thinking of using 2m of 6mm2 cable from the new pump to the batteries and fitting a relay so that the existing wiring can still be used for the switch. Can anyone tell me what relay I need from the VWP website?

 

http://www.vehicle-wiring-products.eu/VWP-onlinestore/relays/relays.php

Edited by blackrose
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Gibbo Veteran II

Gibbo

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Posted (edited)

Those links now seem defunct (apart from Tony's tables), so here's another cable size calculator.

 

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

I'm going to replace a 12v circulation pump (2amp fuse) with a bigger 12v pump which takes a 15 amp fuse. I don't want to replace the 8m of 4mm2 wiring to the switch, so I was thinking of using 2m of 6mm2 cable from the new pump to the batteries and fitting a relay so that the existing wiring can still be used for the switch. Can anyone tell me what relay I need from the VWP website?

 

http://www.vehicle-wiring-products.eu/VWP-onlinestore/relays/relays.php

 

(1) 4-blade 40 amp.

Edited by Gibbo
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