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Is this cable OK for a VSR?


ronnietucker

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I'm hoping to wire up my second (leisure) battery this weekend via a VSR (Voltage Sensitive Relay).

I may have goofed and bought the wrong cables. Are these cables suitable to go from the first battery to the VSR and the VSR to the second battery?

https://www.amazon.co.uk/gp/product/B0711V19RR/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

It describes them as:

  • Sectional battery cable 10 mm2 made in Germany
  • Length: 50cm (distance between the centre of one hole to another)
  • Colour: red, very flexible, very pliable in a PVC sheathing
  • Eyelets: 2 x M5 (provided in mm for the diameter of the eye opening) - high conductivity and dense wall thickness.
  • Application: Battery cable for car, voltage of battery cables is 12 V, suitable for car cable clamps

Just wary as the current cables to/from the main battery is a bit thicker.

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1/ the only two charging sources are the engine and a small solar panel.

2/ the idea is to have the engine connected to battery1 then go to the VSR then to battery2. Battery2 will (from the fuse box) supply the 12V to the LED lighting, and if battery1 drops below a certain threshold it'll be topped up by battery2 via the VSR.

I don't use any 240V shore mains power on the boat. I'm 'off grid'.

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Ok no worries, I think I'd like to know the alternator and solar power's ratings, to answer properly. Also, the conventional "wisdom" is to have the domestic set of batteries as the bank connected to the charging sources, but this assumes the domestics are constantly cycling ie are significantly discharged compared to the starter battery. Yes, the starter battery should be the priority one for keeping a store of energy so it can be used for starting, but in fact the discharge on one start isn't that great, thus its charging requirement isn't great either. This means that if all the charger(s) are connected to it, its "the long way round" to charge the domestics, when in fact there's normally no bother connecting the domestics directly, then having the engine/start battery connected via a relay.

Of course, it gets more complicated if you have 2 alternators but then it opens up additional options, like paralleling them, etc. so don't worry about this.

BUT - big but - in your case, it might well be your domestic demand is so low that in fact the engine/start will need more energy, so the way you have things currently connected would be better. This is easily resolved by doing a power audit - which needn't be overly complicated if you have few demands, ie just a few LED lights. In fact....worth asking....no fridge?

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I'm a simple man. No fridge/TV or anything like that. Just some LED lights and a couple of cigarette sockets for charging phones etc.

Sorry, my mistake, the solar panel will connect to battery1 and the VSR will automatically switch to allow the charge to go to battery2 if battery1 is full.

I'm not sure about the alternator. It's a Suzuki DF15 (outboard) which I think (from a brief search) is 12V 6A.

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Just now, Paul C said:

10mm2 cable will be fine (assuming you don't have a million amps of solar....), just try to be as "efficient" as possible in minimising its length, so that you don't have too great a voltage drop. 

The cables are only about 30cm long. It's really just to put the VSR between the batteries.

Thanks for the advice, guys.

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34 minutes ago, jonathanA said:

Err I think you might run into a problem with the BSS which mandates a min of 25mm cables I think 

I think it would be okay - its not a battery interconnect cable in the traditional sense of those used to join multiple batteries in one bank.

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2 hours ago, ronnietucker said:

The cables are only about 30cm long. It's really just to put the VSR between the batteries.

Thanks for the advice, guys.

 Section 3 of the BSS says 25mm cable min between batteries.  http://www.marinesurveys.net/BoatSafety/Guideline-chap3Electricity.pdf

Edited by Flyboy
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You could be right the bss specifically says battery to battery not battery-VSR-battery but suspect you might be at the examiners interpretation....

i would add that 10mm is a bit weedy IMHO- the issue isn’t how big the alternator is or how many solar panels but what current will flow when the vsr connects a flat battery to a fully charged one (albeit the current will drop very rapidly) 

Edited by jonathanA
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Without getting too technical, I want to run a 12 v supply from an existing socket to the other side of the boat to site another socket. Does it matter what size wires. Is it the bigger the better, or will normal 12v cable be sufficient?

Sorry to nick this thread. It's not completely off topic.

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To answer that question we need to know the size (square mm and length) of the existing cable between fuse and the existing socket, presumably both sockets could be used at the same time, and presumably by socket you mean a car type 12v cigar lighter type, which is usually rated at 10amps.  So if you plan to use both sockets at the same time to power things like laptops or tv, the existing cable may be a bit too small and may give too much voltage drop and or blow the fuse with the extra load.  That way you can see if you need to replace the existing cable or not before thinking about the extension cable.

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11 hours ago, Chewbacka said:

To answer that question we need to know the size (square mm and length) of the existing cable between fuse and the existing socket, presumably both sockets could be used at the same time, and presumably by socket you mean a car type 12v cigar lighter type, which is usually rated at 10amps.  So if you plan to use both sockets at the same time to power things like laptops or tv, the existing cable may be a bit too small and may give too much voltage drop and or blow the fuse with the extra load.  That way you can see if you need to replace the existing cable or not before thinking about the extension cable.

Spot on :)

And what on Earth is...

11 hours ago, Nightwatch said:

normal 12v cable

??

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13 hours ago, Nightwatch said:

Without getting too technical, I want to run a 12 v supply from an existing socket to the other side of the boat to site another socket. Does it matter what size wires. Is it the bigger the better, or will normal 12v cable be sufficient?

Sorry to nick this thread. It's not completely off topic.

In answer: yes; not necessarily; maybe.

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