Battery short (1 Viewer)

[Bart]

I have a battery bank of 3 x 130 AH batteries, Today i had to remove them as i was doing some cable work behind the battery bank and that's when one of the 25 mm positive that goes between battery 2 & 3 connected with something Neutral , as the Positive cable was one going between batteries it was not fused.
Contact was for like half a sec but long enough to burn the edge of the positive lead.
After that i checked the voltage of the 3 batteries before i re connected them together and they were all reading 13.5 volts
After re assembling my battery bank my voltage was reading 13.5v
Could this of done any damage to my battery bank , and if so what ? and how could i check for such damage. ?
Also when using my 1500W Inverter from my battery bank of 390AH ( 3 x 130 AH batteries ) what is the Minimum Voltage that i should let the batteries drop to WHEN UNDER LOAD , with say the microwave going ?

 

[PhilandMena]

Not an expert on this subject, but i would check for blown fuse somewhere in the chain as their maybe no protection on the system and at present your reading current battery voltage immediately after short. Also get some fuse links installed between all your positive leads.

 

[Camping Gaza]

I did read somewhere that a direct short can buckle plates. Count yourself lucky it did not weld itself to that neutral, you would be a mass of flames. I bet you will be getting maxi fuses on all those lines quicker than s**t through a tin horn now! (or you should!)

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[andy63]

Moral of this story... always disconnect the earth first... that way any contact by spanners and wires won't cause what happened to you...
You may have got away with it but I'd be surprised if a fuse hadn't gone somewhere...
Suppose it depends on whether you had disconnected the other positive linking wires and only that battery was involved in the short...
Andy

 

[pappajohn]

A direct short could cause damage....but it would need a bit longer than a quick flash to earth.
The plates won't even get warm, never mind hot enough to warp them.
Old school shunt type battery testers placed a direct short across the battery for 5 seconds or so without harm.

 

[Gromett]

It is possible that it may have damaged the plates but in my opinion if the contact was brief it is unlikely. As others have said get fuses on the cables.

I have a rule of thumb, if it can generate a voltage, fuse it as close to the source of the voltage as possible.
My link cables have a mega fuse at each end. The reason being if one of the batteries went short circuit for some reason it wouldn't pull down the rest of the bank. Not likely but murphies law always kicks you in the sphericals when you are least expecting it

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[two]

Only you know the true extent of any damage that may have been caused. If it was as described, you may not have done significant harm but mark and watch that battery over time. Check its voltage and compare it with the other two (you will need to carefully isolate them to do that). If it shows signs of deterioration, bin it and continue with just two. Otherwise it will draw the others down to its own level and shorten their life also.

 

[Bart]

I was out there again looking at the way i removed the batteries to see what shorted where.
ok i have 3 batteries
batteries 2 & 3 are above battery 1
I disconnected the Negative lead that runs from battery 1 to battery 2 , at the battery 2 connection with the other end still connected to battery 1 (As both battery 2 & 3 need to be removed to access battery 1 which is below them ) i then left it at the base of battery 2 inside the plastic battery box.
Next i then disconnected the Positive lead that runs from battery 1 to battery 2 , at the battery 2 connection with the other end still connected to battery 1 , it was at this stage that when i set the lead down and reached for the insulating tape that the positive lead fell onto the negative lead. so i'm pretty sure if any damage has been done it was to battery 1 and battery 2 & 3 were still connected to each other , but not to the circuit.
What sort of fuses should i get for the 25mm cables ?

 

[Jaws]

You put no more load on it in that brief time than one of the old style battery load testers would do..
Do not worry about it..
Lost count of the amount of times a dropped spanner went across a battery bank in a fork truck.. Bloody workshop looked like something you would see in a meerkat movie every time it happened.. Folk ducking down to floor level in case the batteries had just come off charge !!!

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[Bart]

What SIZE of fuses should i get for the positive cables 25mm2 in size ?

 

[two]

50A

 

[tonyidle]

What SIZE of fuses should i get for the positive cables 25mm2 in size ?

Simply fuse them at around double the anticipated current draw. Say 50A. And Jaws hit the nail on the head: no battery was damaged.

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[Bart]

Simply fuse them at around double the anticipated current draw. Say 50A. And Jaws hit the nail on the head: no battery was damaged.

Thanks , as contact was less than 1 sec i thought it would be ok,, but thought i'd ask just in case.

 

[Bart]

I forgot to say i have a sterling B2B 60A charger installed in my system , and when i installed it i had to put a 80A fuse inline between the B2B OUTPUT and battery 1 , So will the 50A fuses be ok between the batteries ?
See page 4 for the fuse i had to put in
https://cdn.shopify.com/s/files/1/0..._41ed676a-c2b5-45ae-b346-e56ccbfc680a.pdf?479
Also do i only need to put fuses on the Negative connector leads as well ?

 

[peterc10]

50A

That would blow everytime he used his inverter on anything taking more than 600W.

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[Bart]

So for a 1500 W inverter what fuses should I use between each battery , or would I be best taking an amp useage using a clamp meter while the inverter is powering something power hungry ?
Also should I fuse the neutral cables as well as the positive ?

 

[two]

Fuses protect wires. As 25mm2 wires should be taking no more than 50A, you fuse at that level. You’ll need thicker wires and a larger fuse to protect the wires going to a big inverter but three batteries wired in parallel at 50A each would provide up to 150A. The fuses you use will depend on the circuits you employ and what you are trying to achieve.

Don’t fuse the negative side as well. Seek the help of an auto electrician. A mistake could cost you far more than that of their services.

 

[PhilandMena]

I have a Sterling 300W inverter fitted and as per their manufacturers guidelines have a 60 Amp fuse fitted. However, between both factory fitted (from new) leisure batteries their is a 20 Amp fuse fitted to the positive cable.
My take on this, is that the onboard charger will never exceed 20 Amp when charging (Rated and protected at 20Amp) so the 20 Amp fuse is giving the correct protection. I'm now wondering why Sterling recommend I fit a 60Amp fuse when the most I will ever draw is about 5-6 Amps (Lap top). The 20 Amp fuse has never blown even after having the Inverter installed and working.

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[peterc10]

I I'm now wondering why Sterling recommend I fit a 60Amp fuse when the most I will ever draw is about 5-6 Amps (Lap top). The 20 Amp fuse has never blown even after having the Inverter installed and working.

A 300W inverter can handle a peak short term load of 600W, so that suggests 50A, guess they have just added a bit

 

[Bart]

Fuses protect wires. As 25mm2 wires should be taking no more than 50A, you fuse at that level. You’ll need thicker wires and a larger fuse to protect the wires going to a big inverter but three batteries wired in parallel at 50A each would provide up to 150A. The fuses you use will depend on the circuits you employ and what you are trying to achieve.

Don’t fuse the negative side as well. Seek the help of an auto electrician. A mistake could cost you far more than that of their services.

Thanks for the advice , thought i did not need to fuse the negative,, but best to ask.
here is a link to my 1500W inverter :
http://www.sunshinesolar.co.uk/prod...Sine_Wave_Sunshine_Power_Inverter/VP1500.html
Notice it comes with TWO Negative cables & TWO Positive cables , both of which are like half as thick as my 25mm2 cable i use in the rest of the wiring , yet they say to keep it like that.
As the load is Split into two entry points on the inverter. , or it could be 1 for each plug, as it has two plugs.

 

[two]

Two thin wires of 12.5mm2 are as good as one at 25mm2. It’s the total cross-sectional area that matters.

Current will be shared between the wires (keep each colour the same length). The number of input wires will have no influence on the number of output sockets.

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[Bart]

I tried to Max out my 1500W Inverter there to see if it would blow an 80amp fuse i has here and fitted to one of the positive battery cables , i tried a hair dryer there that says 1800W on it,, I was able to run it for 30 secs untill i stopped it without blowing the 80amp fuse , all wires were stone cold after wards.
i have not got a 50amp fuse here to try it ,, but i think it would blow it.


Edit .. mind you i just read on the web how to convert watts to amps.
it said Amps = watts divided by voltage ( for 12v )
so 1500w / 12 = 125 ( amps )
is that correct ? if so surely it would of blew said fuse ? maybe hair dryer wanked out as its ancient SShhh don't tell the wife or she will want a new one

 

[two]

The idea of a fuse is that it blows before the wire melts and the rated current to do so is the minimum required to melt the fuse. I don’t know how much more you could get away with before it would actually blow.

I wouldn’t bother to add fuses to the wires joining your batteries together, but do put a megafuse between your inverter and the battery bank (150A). I’d expect all the distribution wires from the battery to other devices to be fused, somewhere.

 

[Bart]

I wouldn’t bother to add fuses to the wires joining your batteries together, but do put a megafuse between your inverter and the battery bank (150A). I’d expect all the distribution wires from the battery to other devices to be fused, somewhere.

Already done when i installed the inverter , same for the B2B charger , it has 3 fuses , 1 at negative , 1 at cab bat >> B2B charger , then the last at B2B >>> Battery bank

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[peterc10]

This all depends upon how you have connected the batteries in the battery bank to the equipment. I have followed Hymer's advice which says (for 2 batteries) to put all the positives to one battery and all the negatives to the other one. They say that this ensures that high takes off from things like an inverter is shared between the batteries. If that is the case then I guess there will be a lot of flow through the connecting wires between the the batteries

Others put all the positives and negatives on one battery - that is what I did in my last motorhome. In that case I guess the flow will be less.

 

[Bart]

The idea of a fuse is that it blows before the wire melts and the rated current to do so is the minimum required to melt the fuse. I don’t know how much more you could get away with before it would actually blow.

I also took out our Variable power ( something like 1400W > 2000W ) hover out to the MH within the last 30 mins to see how far i could ramp it up , so i knew the inverter was maxing out .
so boost control step 2 of 5 = passed ok , inverter still running , no fuses blown , next boost control step 3 of 5 = passed ok , inverter still running , no fuses blown ,
Next boost control step 4 of 5 = Failed , inverter stopped running , no fuses blown.
So i was able to draw all my max power from the inverter and the 80 Amp fuse lived.
Think ill stick with the 80 Amp fuse.

 

[Bart]

This all depends upon how you have connected the batteries in the battery bank to the equipment. I have followed Hymer's advice which says (for 2 batteries) to put all the positives to one battery and all the negatives to the other one. They say that this ensures that high takes off from things like an inverter is shared between the batteries. If that is the case then I guess there will be a lot of flow through the connecting wires between the the batteries

Others put all the positives and negatives on one battery - that is what I did in my last motorhome. In that case I guess the flow will be less.

I have 3 batteries in my bank
all 3 positives from batteries connected together, then positive feed from battery bank out via battery no.1
next all 3 negatives from batteries connected together then neutral feed from battery bank out via battery no.3

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[tonyidle]

How long are the connecting wires between batteries? If they're as short as I suspect (around twice the height of a battery or less) there's no point in putting a fuse in anyway. The only reason to put a fuse in a link cable is if it is long enough to be damaged or near sharp metal parts (in which case it should be sleeved anyway).

 

[Bart]

How long are the connecting wires between batteries? If they're as short as I suspect (around twice the height of a battery or less) there's no point in putting a fuse in anyway. The only reason to put a fuse in a link cable is if it is long enough to be damaged or near sharp metal parts (in which case it should be sleeved anyway).

link between battery 1 & 2 = aprox 1 ft link between battery 2 & 3 = aprox 1 meter
ive put in a few 80 amp fuses i had extra anyways ,, do no harm, and they aint blowing when inverter running at max.