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Additional Leisure Battery blowing fuse


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Hi, I have recently put in two new leisure batteries. 2x120Amphours linked in parallel with the poitive connected to one battery and the negative to the other so that they drain down equally. However once connected a 20amp fuse to the ‘internal charging module’ blew immediately. Tried three times, same result.

can anyone advise as to whether it is safe to increase the ampage of the fuse or is this likely to damage the onboard appliances/accessories? Or do I need either a larger inverter or perhaps a resistor between the batteries and the fuse?

Thank you in anticipation of your help.

Regards

Terry

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Posted (edited)
1 hour ago, GuyGuerilla said:

Hi, I have recently put in two new leisure batteries. 2x120Amphours linked in parallel with the poitive connected to one battery and the negative to the other so that they drain down equally. However once connected a 20amp fuse to the ‘internal charging module’ blew immediately. Tried three times, same result.

can anyone advise as to whether it is safe to increase the ampage of the fuse or is this likely to damage the onboard appliances/accessories? Or do I need either a larger inverter or perhaps a resistor between the batteries and the fuse?

Thank you in anticipation of your help.

Regards

Terry

There are some members on here with excellent electrics knowledge but I suspect a lot more detail will be needed before anyone can assist much:-

1. 'internal charging module' -  make, model, part of a power/distribution unit, if so which one?

2. not sure where/how the inverter is involved as you say the fuse blew immediately - on switching on inverter or just connecting batteries?  Make, model, size of inverter?

3. ideally a simple schematic of installation would help

It is impossible to say if a larger fuse is the remedy and a resistor in the feed is not the answer.  You must get to the root cause of the fuse blowing, then apply the remedy

Edited by arthur49
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19 hours ago, GuyGuerilla said:

...................can anyone advise as to whether it is safe to increase the ampage of the fuse or is this likely to damage the onboard appliances/accessories? Or do I need either a larger inverter or perhaps a resistor between the batteries and the fuse?

Thank you in anticipation of your help.

Regards

Terry

Do not do this!!!

The fuse is there to protect the wiring from overload.  That the fuse is blowing indicates that connecting the two batteries as you describe has resulted in either 24V being fed into the circuit instead of 12V, or that the combined load of the two batteries exceeds the safe capacity of the installed wiring.

From your description, uprating the fuse would be likely to result in very hot wiring, possibly to the extent that it burns out and catches fire.  It that is the case the reaction from the wiring is likely to be almost instantaneous, and not stoppable.

I'm sure someone with greater knowledge then me will be able to give constructive guidance on what is wrong.

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As Brian says, don't increase the fuse.

I would seem that it is most probable you have done something wrong, I find remote analysis or electrics most frustrating, but here's a few ideas.

Are you sure you have connected the batteries in parallel and not in series. Maybe there is a fault in wiring which is now causing a short. As an outside bet, maybe one of the batteries has a internal short.

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I Agree with everything written so far, You need to check and upgrade the circuitry before fitting higher amp fuses.

It MAY OR MAY NOT be a smaller fuse has been fitted and a bigger fuse would be ok.

But only a fool would say yes its ok to bung a bigger fuse in without a lot more info.

As Keith says, if you post a few photos and show us what you have done we may be able to help.

Otherwise it needs to go in to an auto electrician.

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Terry,

Since your first post, you have been given sound advice by several forum members, some of whom have requested further information so that there advice may be more specific.  So far you have failed to comply with these requests, and responded by repeating your questions under a different heading.

Your second sentence reads " 2x120Amphours linked in parallel with the poitive connected to one battery and the negative to the other so that they drain down equally."

I am hoping that you appreciate the difference between parallel and series connection of batteries.  To confirm, with parallel connection the positive terminals of both batteries must be connected together, likewise both negative terminals must be connected together.  Tradition demands that the load/charging positive connection should be made to one battery positive terminal, and the negative connection to the other battery negative terminal.

Check carefully to confirm that you have achieved a parallel conection.  Without this confirmation and more information regarding your system, I doubt that the forum will be able to assist further.  I will add however that I as well as others are puzzled by your mention of an inverter.  Please explain what it's function is.

Alan

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Hi All and many apologies for what must to all of you seem a very tardy response!

When I first tried to post my enquiry I didn’t think it had been accepted as I hadn’t logged on and then couldn’t remember my password!

I then re-entered my post on Sunday after which I then discovered everybody’s comments on the initial posting.

Having now read all of your suggestions and concerns for which I thank you all very very much, I have decided to find a suitable professional who can hopefully sort out my electrical issues.

Thank you all once again for all your extremely pertinent comments.

Regards

Terry

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Two 12 v batteries connected to each other + to - sounds like series and would produce an exit voltage of 24 v.

Two 12 v batteries connected + to + and - to - is the recognised pattern or parallel in which the exit voltage remains at 12 v. The connecting cables should ideally be capable of carrying a heavy current to ensure less internal reistance.

By connecting the hab feed and charging cables + to + on one battery and - to - on the other a more even discharge and charge distribution is theoretically attained.

There may well be, or not be, evidence to support that theory.

NEVER replace a blown fuse with a higher amperage rating without first ascertaining what the correct fuse value shoud be - probably the same as it was when you just had one battery.

I have done this quite a few times over many years without issues but a fuse blowing should always be taken as a warning that something ain't right.

Once all is connected and working feel all connections for security and temperature. If something gets hot or even warm is suggests high resistance and wrong. Might only be loose or dirty but it needs sorting before a fire starts.

I have no electrical training or qualifications - just a bit of experience and some common sense!

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Hi 

Re trace your steps on what you carried out, re the batteries . Maybe disconnect and re try with one battery and with  correct amperage fuse as was fitted originally  Always find the source of your problem and never just uprate your fuse to a higher amperage. You may have a fire on your hands otherwise . You have been given good advise by all here .If your not competent with DC wiring , get a good Auto electrician to check it out for you and be safe 

Regards

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Perhaps not expressed in the best way but I suspect the op has connected both battery positives together and then both battery negatives together. He then connects this 'battery bank' to the motorhome by feeding the positive from one battery and the negative from the other. Thus particularly under higher current flows there is balance.

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On Monday Guy said

...Having now read all of your suggestions and concerns for which I thank you all very very much, I have decided to find a suitable professional who can hopefully sort out my electrical issues...

Based on Guy's postings, this seems (to me) to be the wisest way forwards, and - after the problem has been resolved - it would be nice if Guy could let the forum know what the fault turned out to be and how it was fixed.

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1 hour ago, Derek Uzzell said:

it would be nice if Guy could let the forum know what the fault turned out to be and how it was fixed.

Yes it would

Unfortunately some people don't bother

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Hi Derek

Maybe just testing the forum as to who would give incorrect or unsafe advice on the topic, May not be Terry's agenda but many first time posters are I am informed, this is happening quite a lot on many different forums without reply. I think all on here just want to help and give their "tuppence worth" which can hopefully help so many with problems that can arise from time to time. I personally think Terry is correct if unsure about his electrical issue to seek further professional help.Yes lets see will Terry get back to us as to how he got on. Hopefully he will. 

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