I work in a plant where we have a PSU supplying 5V 200A DC to an electronic circuit, the connection from the PSU to the electronics is fed via a heavy duty multistrand cable, this is crimped at both ends. The electronics is very sensitive to volt drop so in order to improve stability it has been suggested that the cable is re terminated with crimps, and then the crimps soldered.


I am sure that this is not recommended but I cannot find the information anywhere to confirm this, can anyone on this forum offer me any advice?

Many thanks

If the crimps are made off properly, what will the soldering achieve?

If your concerns are around vibration, then soldering can reduce mechanical stability of a multi-stranded cable termination by "wicking" up the conductor and losing your flexibility - this may also increase volt-drop and cause other problems.

With lead/tin solder, migration of the elements in the solder over time because of pressure at the termination causes a problem; the situation is different with modern lead-free solders, but still a consideration.

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Eur Ing Graham Kenyon CEng MIET

Thanks for your reply, its interesting how something that in theory should improve stability can actually have the opposite and could also be considered dangerious if the mechancical stability of the cable is under threat.

Are you aware of any regulations that cover this? I have looked through the BS 7671 but cannot find any information on this subject.

I dont think you will find any regulations. I would contact the crimp makers, they are usually happy to tell you how good their product is and why.

As far as I know, only BS7671 Section 526 contains a requirement to consider the effects of soldered joints (526.2, para above NOTE 1), although the selection of any joints would have to conform to other parts of this Section too (as well as other relevant parts of BS7671).

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Eur Ing Graham Kenyon CEng MIET

Why do you reckon you never see soldered connections in car electrics? Is this because of cost saving or electrically safer?

Both probably - today, time taken to make the connection is far greater using soldered joints. Another consideration is that soldered joints can be quite resistive, and of course in ELV power applications, resistive joints are not good. There are of course methods that we may now call "old-school", for making low-resistance soldered joints in power cables, but I would very much doubt if those skills are still being taught.

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Eur Ing Graham Kenyon CEng MIET

The real problem with soldering crimped joints is getting the solder inside the terminations as a gap-filler. The art of soldering lies in getting the solder to flow into the surfaces that are to be joined. This is why it is essential to first clean and then to "tin" those surfaces .

It is also essential to get the joint up to the correct temperature for the solder-mix to be employed.
Too hot and you burn away the component with the lowest melting point.
Too cold and you get a "dry joint".

Correct flux also helps - its function is to dissolve any oxides formed from the air-borne Oxygen. Again too much is as bad as too little.

My solution would be to divide the dc into separate strings and insert voltage stabilisers. It would have been a better engineering design to have used several smaller dc units.

Ken Green

As mentioned above, vibration is an issue.

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Richard Winstone MIET

All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
Irish orator, philosopher, & politician (1729 - 1797)