Dodgy Inverter connections

[Ex- Member]

Had a bit of a problem earlier today. Washing machine was running whilst cruising for water. 30 minutes later Lynn notes the washing machine stopped. We pull in the water point and it seems there's no 240v, check inverter no power Inverter dead. Battery bank reads 12.6v

 

I then checked the 200a Maga fuse on the 12v supply to the Inverter, the fuse enclosure was hot. I removed the fuse and did a quick check by running volts through it and checking with a volt meter. It showed a reading so thought the mega fuse was ok.

 

So I removed the inverter, a right PITA and weighs a ton and tucked away in a cupboard.

 

Anyway on removal from the bulkhead fixing I just had the 2 heavy 12v cables to remove. I removed the live cable using the M10 grub screw. On the Neg cable though, "to my surprise", the grub screw is missing and cable is loose and simply pulls out of the housing.

 

The inverter has been fixed against a bulkhead wall and the only place the missing grub screw could be is at the base of this bulkhead as the slipper stern slops and ends at that point.

 

Anyway we search for the screw, and can find no sign of it at all. I recall cleaning this area out when we fitted the battery bank which was a good 18 months ago. The area at the base of the inverter would have been cleaned and Hoovered out. So that grub screw must have come away from the inverter some time before that, and got sucked up in the hoover.

 

So It seems the inverter has been running with a loose negative connection for well over 18 months.

 

We can't fathom what the problem is with the inverter not working today though. I then notice the 12v power is also down. I then think, hang on, it must be the mega fuse!

 

On double checking it was indeed the Mega fuse as I used the volt meter on the outlet of the fuse and no voltage was recorded.

 

I had really made a stupid schoolboy error and hadn't checked the fuse properly earlier. However this error actually lead me to the fault that being the loose Neg cable to the inverter.

 

I managed to find some M10 thread and form another grub screw. All Is now fitted back, Mega fuse replaced and all running fine.

 

I'm really glad my stupid error in checking the fuse led me to this problem. I'm amazed the Neg cable never fell out of It's housing of even worse shorted somewhere, there's no sign of any burn damage either. We have noticed that an occasional flickering of LED lights seems to have stopped.

 

Would have this loose connection have compromised electrical performance.

[Chalky]

You're lucky the connection didn't overheat and cause a fire. Any high current connectors should be done up 'king' tight.

[Captain Fizz]

I love the use of technical engineering terms Chalky!

[Ex- Member]

You're lucky the connection didn't overheat and cause a fire. Any high current connectors should be done up 'king' tight.

 

Possibly why the fuse blew then. We've run the washing machine before though without issue, but with engine running vibration etc I suppose anything is possible.

 

I'm just glad I found it, Maybe it was fate, as it was such a dumb error that lead me to removing the inverter in the first place.

[smileypete]

What was the grub screw on, the fuse holder, if so what sort of fuse holder was it?

 

For high current particularly I'd always prefer a properly crimped ring terminal and bolt, and not the little socket screws on the 'bling' type car fuseholders. Solar controller screw terminals can also loosen off and overheat causing damage.

 

Where screw terminals are unavoidable with fine stranded wire like on solar controllers, there are heavy duty pin terminals available but they're not easy to come by:

 

http://davico.co.uk/product/heavy-duty-pin-connectors/

 

Or just use ferrules on the end of the wire but they might not take as much welly on tightening as the pin terminals will.

 

ETA PDFs with a bit more about it:

 

http://www.nmsu.edu/~tdi/pdf-resources/CC104.pdf

http://www.nmsu.edu/~tdi/pdf-resources/IAEI-1to2-05.pdf

 

cheers, Pete.

~smpt~

Edited January 20, 2014 by smileypete

[Ex- Member]

What was the grub screw on, the fuse holder? What sort of fuse holder was it?

 

For high current particularly I'd always prefer a ring terminal and bolt, not the little socket screws on the 'bling' type car fuseholders. Solar controller screw terminals can also loosen off and overheat causing damage.

 

cheers, Pete.

~smpt~

 

These are the positive and Negative connections on the inverter Pete. They are quite sturdy, the cable is pretty thick, looks around 120mms The cable ends are tinned and slot into some quite thick metal tube with plastic covers, the grub screws are M10 and once the cable in in the tubular bit you just tighten the grub screw. I do have them tight with a good heavy screwdriver. But I thought that originally, I'm usually one who over tightens stuff and fecks up the thread

 

Anyway something to check periodically for sure. All the other connectors are now ring terminal. A 60 amp fuse I did have on the solar input failed miserable. Now been replaced with Mega fuse bolted M8

 

The inverter has been fitted over 7 years, I wonder how long the grub screw has been missing.

[smileypete]

 

These are the positive and Negative connections on the inverter Pete. They are quite sturdy, the cable is pretty thick, looks around 120mms The cable ends are tinned and slot into some quite thick metal tube with plastic covers, the grub screws are M10 and once the cable in in the tubular bit you just tighten the grub screw. I do have them tight with a good heavy screwdriver. But I thought that originally, I'm usually one who over tightens stuff and fecks up the thread

 

If you mean the ends were tinned with soldering iron and solder, there's your problem right there.

 

Problem is the solder will creep under pressure and end up with a loose connection with too high resistance and likely overheat, so cable ends to go under screw terminals should never be tinned with soldering iron and solder.

 

cheers, Pete.

~smpt~

[Ex- Member]

 

If you mean the ends were tinned with soldering iron and solder, there's your problem right there.

 

Problem is the solder will creep under pressure and end up with a loose connection with too high resistance and likely overheat, so cable ends to go under screw terminals should never be tinned with soldering iron and solder.

 

cheers, Pete.

~smpt~

 

 

Funny you mention that, it didn't actually look like solder, I just assumed, but the ends had no lose strands and remained tightly packed. It wasn't like the usual tinning you see though I must say. The cables were supplied with the inverter as well. maybe it's some kind of resin, it is Silver looking strands though.

[Sierra2]

'Thread Lock paste' seems to be missing in terms of advice. As a motorcyclist who services his own bikes this (or lockwire) is the norm. Is this not the case on boats? (asked as a newbie to boating). Chaz

[Keeping Up]

No thread locking compound would help if the wire was tinned with solder. As Pete says, the solder would creep until the connection was loose.

 

I once tinned the end of a battery cable that was clamped by a screw, because my BSS inspector insisted on it. I found that I had to re-tighten the screw once every 2 to 4 weeks, until I lost patience with it and cut the tinned part off.

[nb Innisfree]

A few years ago I started a thread about our overheating mega fuse. No idea why it happened but since then I have regularly checked by feeling around all heavy connections for any undue heat.

[Keith M]

I have to say that an inverter using 120 mm ²

I would not be happy using grub screws to retain the cables of that CSA

Nuts and bolts

 

Keith

[mayalld]

Had a bit of a problem earlier today. Washing machine was running whilst cruising for water. 30 minutes later Lynn notes the washing machine stopped. We pull in the water point and it seems there's no 240v, check inverter no power Inverter dead. Battery bank reads 12.6v

 

I then checked the 200a Maga fuse on the 12v supply to the Inverter, the fuse enclosure was hot. I removed the fuse and did a quick check by running volts through it and checking with a volt meter. It showed a reading so thought the mega fuse was ok.

 

A common diagnosis error.

 

A blown mega fuse will often appear to conduct when removed from its housing, because the two ends move relative to each other and make a new contact.

 

When testing a mega fuse, ALWAYS check whether the lugs can be moved independently. If they can the fuse is cream crackered, no matter what the continuity test says.

I have to say that an inverter using 120 mm ²

I would not be happy using grub screws to retain the cables of that CSA

Nuts and bolts

 

Keith

 

I assume that this is a Sterling inverter. They are fitted with holes to accept the supplied diameter cables, using a grub screw. They recommend tightening the grub screw every few months, and I've never had any problem with ours.

[Keith M]

My concern in using a grub screw is that as the cable is compress there is only a small section of cable which is under pressure

 

Keith

[mayalld]

My concern in using a grub screw is that as the cable is compress there is only a small section of cable which is under pressure

 

Keith

 

That may well be the case, but this is the connection that is fitted to these inverters. Without starting to butcher the thing there is very little that can be done other than to use the supplied fittings

[Timleech]

My concern in using a grub screw is that as the cable is compress there is only a small section of cable which is under pressure

 

Keith

 

I think there was probably a cable ferrule supplied with the inverter when new.

I have one of a similar type, bought secondhand, came with no ferrules but I used a segment of copper tube to spread the pressure from the grub screw.

I'd prefer a proper crimped & bolted lug, but that system seems to work provided it's assembled carefully.

A similar arrangement with either a tubular ferrule or strip of copper or brass is often used with welding cable fittings such as earth clamps and electrode holders.

 

Tim

[smileypete]

Where screw terminals are unavoidable with fine stranded wire, best use a properly crimped on pin terminal or ferrule.

 

In a pinch it might be possible to crimp on a ring/butt connector, then cut the other half off so the crimped on half acts as a ferrule. Even a ferrule crimped on with pliers should be a lot better than nothing.

 

cheers, Pete.

~smpt~

Edited January 21, 2014 by smileypete

[Keeping Up]

I have a ratchet crimping tool for the red/blue/yellow insulated crimps and a cheaper tool for the uninsulated ones, but what is the correct tool for a ferrule?

[Chalky]

At work we have a hydraulic crimping tool that's used for putting terminals and ferules onto large diameter cables. You fit the correct set of dies, insert the cable and terminal and pump away until the correct crimp is achieved at which point the device opens and releases the finished crimp. It puts a hex crimp in the termination and also embosses the size of the crimp on it - useful for verifying the jobs been done correctly. We crimp all cable connections, they're never soldered. A proper crimp will cold weld onto the cable and will last the life of the product.

[Keith M]

I would be more than happy if a cable ferrule has been used or some other similar item

 

My concern was with just a striped end of cable inserted and retain by the grub screw

 

Keith

[nicknorman]

I have a ratchet crimping tool for the red/blue/yellow insulated crimps and a cheaper tool for the uninsulated ones, but what is the correct tool for a ferrule?

Something like this.

http://www.farnell.com/datasheets/7149.pdf

 

Or, cheaper, like this

 

http://www.rapidonline.com/Cables-Connectors/Crimp-Tool-for-Bootlace-Ferrules-0-5-to-4mm-85-0276

Edited January 21, 2014 by nicknorman

[Ex- Member]

Hi all

 

All is working fine now, ran the washing machine earlier, connections were hardly luke warm. The 200a fuse that blew I actually replaced with a 100amp as I didn't have a spare 200a. (Now on order) It didn't blow that so it seems the initial loose Neg connection to inverter was most probably the culprit. I know to check there regularly now. I'm not going to mess with the inverter connections it's what came with the inverter and the cables are connected as the instructions require.

 

I don't know when this grub screw removed its self, but the inverter has run faultlessly for over seven years. The screw is a M10 and can be tightened quite robustly.

 

The model is an Invertek PSI 3kva

 

http://japanese.alibaba.com/product-free/dc-ac-invertek-low-freq--10986322.html

 

It's been superseded with newer models since of course. On removal I was pleasantly surprised at it's general condition. No rust corrosion not even flaking paint. what I could see internally all looked good and clean. Having been in the engine room for seven years and suffered long periods of non use as well as long periods of heavy use, it seems to be holding out pretty well.

Edited January 21, 2014 by Julynian

[Timleech]

The one I have has been fitted with socket (Allen) head grub screws, no idea whether original or not, these can certainly be tightened thoroughly.

 

Tim

[raymondh]

Any RCD experts out there ? I think bare conductor connections are a fail as not compling with the BS EN ISO 10133 10.3

 

Ray

[nicknorman]

Any RCD experts out there ? I think bare conductor connections are a fail as not compling with the BS EN ISO 10133 10.3

 

Ray

Yes ISO 10133 does require wires connected to studs or screw connections to have suitable terminals. However, it is only necessary to comply with the RCD for a new build.