Jump to content
KiwiTR6

Beware of voltage drop!

Recommended Posts

Now that my new alternator is installed I have been checking the charging system to ensure all is as it should be.  In hindsight I should have done this before changing the alternator but I would have gone ahead with that anyway just for peace of mind.

First up, I found that I had 14.2V at the alternator but a drop of nearly 1.0V at the battery (reading 13.2V).  Time to start looking.

Checking the heavy brown wire at the connector to the starter lead I quickly found where part of the voltage drop was - the clear rubber terminal boot had folded over and was preventing full contact. Fixed that problem and I now had a 0.5V drop to find.

I had a sneaking suspicion that the terminal block moulded to the starter lead (what a horrid idea that is) could be suspect, so I made up a jumper lead and connected the heavy brown wire direct to the battery.  Voltage drop now down to 0.14V and problem solved.

Hoping this experience may be of help to other owners at some point. 

15715401037930.jpg

Edited by KiwiTR6
Copied earlier post in error.

Share this post


Link to post
Share on other sites

When you posted earlier today on another post  I was going to add that voltage drop and overheating was the reason I limited my alternator upgrade to reworking the existing  Lucas to 45 amps.

I looked at modifying  80+ amp GM alternators and decided that I was getting in the realm of putting welding level  currents through my 50 year old wiring loom. In particular in my 69 CP  the current goes through the dash loom to the ammeter -which is a good incentive to let sleeping dogs lie.

I assume that you are confident that your wiring can safely handle your new alternator's output.

Share this post


Link to post
Share on other sites

Putting on a bigger alternator does not in itself increase the current. The current drawn is determined by the loads not the alternator, so if you haven't changed anything else then going from a 45A to an 80A one will make no difference to the current drawn - it's just that the bigger one will be capable of supplying the higher current if asked to.   

If you do install beefy accessories than then wiring for those should be suitable for the current they draw.

Share this post


Link to post
Share on other sites

I'm talking about charging current after a difficult starting episode- the current that goes to the +40 or so mark on the ammeter.

Share this post


Link to post
Share on other sites
17 hours ago, KiwiTR6 said:

Now that my new alternator is installed I have been checking the charging system to ensure all is as it should be.  In hindsight I should have done this before changing the alternator but I would have gone ahead with that anyway just for peace of mind.

First up, I found that I had 14.2V at the alternator but a drop of nearly 1.0V at the battery (reading 13.2V).  Time to start looking.

Checking the heavy brown wire at the connector to the starter lead I quickly found where part of the voltage drop was - the clear rubber terminal boot had folded over and was preventing full contact. Fixed that problem and I now had a 0.5V drop to find.

I had a sneaking suspicion that the terminal block moulded to the starter lead (what a horrid idea that is) could be suspect, so I made up a jumper lead and connected the heavy brown wire direct to the battery.  Voltage drop now down to 0.14V and problem solved.

Hoping this experience may be of help to other owners at some point. 

15715401037930.jpg

Hi Gavin,

   what are the black boots for over the orange wires.  I am looking for something to go over the Lucas bullet connectors (single and double)

 

Hi Mike,

I would be amazed if you got near 40amps charge after a difficult start.

30 amps probably for a few seconds then reducing to 20, 10, 5 over a few minutes and staying 5 until it is happy.

Roger

 

 

Edited by RogerH

Share this post


Link to post
Share on other sites

I know it's only for a short period of initial charge but I just don't want to smell cotton/rubber insulation burning behind the dashboard.

Share this post


Link to post
Share on other sites
8 hours ago, RogerH said:

Hi Alan,

   what are the black boots for over the orange wires.  I am looking for something to go over the Lucas bullet connectors (single and double)

 

Hi Mike,

I would be amazed if you got near 40amps charge after a difficult start.

30 amps probably for a few seconds then reducing to 20, 10, 5 over a few minutes and staying 5 until it is happy.

Roger

 

 

Hi Roger.

Yes they are in-line fuse holders as John says, one on the main supply to the Bosch fuel pump and the other supplying power to my ex Audi brake vacuum pump, both direct from the battery.  In due course these will be replaced with a supplementary fuse box but they work for the time being.

Cheers

Share this post


Link to post
Share on other sites
12 hours ago, Mike C said:

When you posted earlier today on another post  I was going to add that voltage drop and overheating was the reason I limited my alternator upgrade to reworking the existing  Lucas to 45 amps.

I looked at modifying  80+ amp GM alternators and decided that I was getting in the realm of putting welding level  currents through my 50 year old wiring loom. In particular in my 69 CP  the current goes through the dash loom to the ammeter -which is a good incentive to let sleeping dogs lie.

I assume that you are confident that your wiring can safely handle your new alternator's output.

Hi Mike.

From what I've read this particular 70A alternator is a common upgrade for the car.  It bolts straight up to the existing mounts, the only tricky part is modifying the existing pulley (as I did rather than looking for something else suitable) to get the alignment spot on, and connecting the wiring which are studs rather than terminals.

The loom is a Moss replacement, so no cotton/rubber insulation in sight!

Door cards off and mirrors on today - a much more daunting task....

Gavin

Edited by KiwiTR6
Clarification

Share this post


Link to post
Share on other sites

And I just checked - you have a 73 TR which should have a voltmeter and a much more direct path between the battery and alternator.

I agree with  you on the door cards and mirrors, visible work on the body is far more daunting and less forgiving of any mistakes.

Share this post


Link to post
Share on other sites
32 minutes ago, Mike C said:

And I just checked - you have a 73 TR which should have a voltmeter and a much more direct path between the battery and alternator.

I agree with  you on the door cards and mirrors, visible work on the body is far more daunting and less forgiving of any mistakes.

Yes a voltmeter that reads 1.0V low, but I'll get that sorted in time. Almost direct as you say, but it's where it connects to the starter lead that I was losing 0.5V.  Its a horrid connector block moulded to the lead wire, I'll be removing all connections from that point and routing them via a supplementary fuse box direct to the battery +ve with the heavy alternator supply wire also going direct to the same point.  I've changed that temporarily at this stage with a short jumper lead. 

Share this post


Link to post
Share on other sites

And I'd solder every connection I can, if voltage drop looks like being a problem I'd even solder wire tails to be fitted to screwed sockets.

Share this post


Link to post
Share on other sites

Mike,

I was always told NOT to tin the ends of wires that go into screw connectors.

Apparently over time the solder will “Creep” sideways under the compression of the screw and you end up with a loose joint.

Well… That’s what I was told as an apprentice.

 

Charlie.

Share this post


Link to post
Share on other sites

This topic (crimping versus soldering or even both) was discussed a couple of years ago. Opinions and preferences differ.

I use crimping connectors, not the poor red/yellow/blue ones, but the ones that also crimp the wire isolation to the connector to it is more rigid. You need a special tool, which is more expensive (they start at around 30 euro), and also some money goes into ordering a collection of connectors and sleeve. Soldering does not hold/secure the wire Itself to the connector, and can give corrosion if not properly cleaned after soldering. And proper cleaning is difficult since the acid will suck into the isolation by the capillary action.

The above is just my opinion.

Waldi

Share this post


Link to post
Share on other sites

I believe that aerospace practice (Roger?) eschews soldering in favour of crimping.      The reason I've been told is that solder tends to 'wick' by capillary action between the strands of the cable, stiffening the conductor away from the connection, so that fatigue and breakage is more likely.

John

Share this post


Link to post
Share on other sites

Indeed we have had that debate before.  A crimp made with a proper ratchet crimp-forming tool can certainly be relied on.  A crimp using one of those 'bent-tin' pliers - maybe not so much.

Soldering should not cause corrosion unless you are using the wrong flux. An acid flux is definitely not the right type. 

Share this post


Link to post
Share on other sites

Thanks Rob,

the acid based flux is what I’m familiar with. No good.

What flux would you recommend for electric connection soldering?

Cheers,

Waldi

Share this post


Link to post
Share on other sites
52 minutes ago, john.r.davies said:

I believe that aerospace practice (Roger?) eschews soldering in favour of crimping.      The reason I've been told is that solder tends to 'wick' by capillary action between the strands of the cable, stiffening the conductor away from the connection, so that fatigue and breakage is more likely.

John

Hi John,

quite so. Aerospace have used crimped terminals for many many decades.

Before they were used they were extensively tested to ensure they were as good as solder joints (regarding conductivity),

Mechanically crimped joints are far superior to solder and they are easier to perform when remote from the workshop.

I know you can get gas powered portable soldering irons but that doesn;t make them better.

 

Roger

Share this post


Link to post
Share on other sites

Its easiest to use a flux-cored solder intended for electrical work Waldi, similar to this:

https://www.amazon.co.uk/Weller-40-100-Electronic-Solder-Resin/dp/B0001P1724/ref=sr_1_6?keywords=flux+cored+solder&qid=1571662665&sr=8-6

(just for illustration - you can get similar solder cheaper than that. There is a wide choice of solder both tin/lead and lead-free and some fluxes are rosin-free as well, mainly due to health concerns. Personally I stick to the old tin/lead and rosin core stuff because I know that works. Some of the lead-free stuff doesn't seem to work as well and needs higher temperatures. It may also not be fully compatible with joints on old circuits when doing repairs.)

The flux is usually rosin-based, which is basically pine resin, but  there are some health concerns over long-term use as the fumes are a 'sensitiser' and can cause asthma. Generally only a problem for people using it day-in day-out as part of their job. It isn't really necessary to remove the residue from that type of flux as it forms a hard varnish-like layer.

If you must use a flux paste then make sure it specifically says it is for electrical work like this:

https://www.amazon.co.uk/MG-Chemicals-Rosin-Flux-Paste/dp/B01MS04SO4/ref=pd_sim_328_2/259-0048478-8658313?_encoding=UTF8&pd_rd_i=B01MS04SO4&pd_rd_r=e780069f-2d9b-4488-800d-ef900833af57&pd_rd_w=FeqtD&pd_rd_wg=onZAD&pf_rd_p=e323aefa-0fb8-4e75-9bef-479c25fd70eb&pf_rd_r=FES298YG815FFKK6QWCR&psc=1&refRID=FES298YG815FFKK6QWCR.

Edited by RobH

Share this post


Link to post
Share on other sites
4 hours ago, Andy Moltu said:

Crimp/compression joints would not normally be soldered

They are if you terminate to the MOD spec for vechicle wire termination! Crimp first then solder!

Bruce.

Share this post


Link to post
Share on other sites
32 minutes ago, RogerH said:

I know you can get gas powered portable soldering irons but that doesn;t make them better.

 

Roger

Oh it does they are so handy, Ive been using them since they came out in the early eighties, best Irish invention!

Stuart.

Share this post


Link to post
Share on other sites
1 minute ago, astontr6 said:

They are if you terminate to the MOD spec for vechicle wire termination! Crimp first then solder!

Bruce.

Which is what I have been doing for the last forty odd years.

Stuart.

Share this post


Link to post
Share on other sites
34 minutes ago, RogerH said:

Hi John,

quite so. Aerospace have used crimped terminals for many many decades.

Before they were used they were extensively tested to ensure they were as good as solder joints (regarding conductivity),

Mechanically crimped joints are far superior to solder and they are easier to perform when remote from the workshop.

I know you can get gas powered portable soldering irons but that doesn;t make them better.

 

Roger

Also Roger crimps are subject to the pull off test and the crimper should have been calibrated. Mr average, I doubt will have that level of equipment.

Bruce. 

Share this post


Link to post
Share on other sites
4 minutes ago, stuart said:

Which is what I have been doing for the last forty odd years.

Stuart.

So have I!

Bruce.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.