Separate Alternator cable for D3

[Ean Austral]

Gday All,


There are several threads about the D3 alternator shorting and the car dying with a dead flat battery. Several people smarter than me believe that the Alternator needs a separate fused cable rather than the original cable that runs from the starter motor to the alternator.


This is my effort at doing the cable, and as I was changing the main drive belt and checking the idler / tensioner bearing so had the fan and the other bits off thought it was the perfect time.
You need
2.5 mtrs 2 B-S cable, or a cable that can handle at least 200amps this cable is 255amp rated plus 4 terminal lugs to suit.
a suitable fuse holder and fuse, mine is a marine type and fitted with 175 amp fuse.
13mm spanner, cable ties , some conduit or cable wrap, and some spare skin for your knuckles.
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705073555_88523.jpg

http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705063121_26848.jpg
So get the engine bay to this stage and you can access the top of the alternator on the left hand side, use the 13mm spanner to undo the lug, remove the old cable and fit the new cable.
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150628071128_38576.jpg


http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705073640_16705.jpg
So this is decision time, unbolt the eye off the starter and cut the old cable off or leave it on. It is a pain to put the nut back on the starter so think about it , you could maybe tape it up and cable tie it out of the way. The cable has the eye and the heat shied taken from the old cable where it bolts onto the alternator
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705063408_25904.jpg


Ok so when the new cable is on the alternator lug and tight ( and you finally manage to get the cable back on the starter if you have gone to that length ) you need to follow the starter cable down and under the engine and up in to the passenger side to where the battery is , ( you will see under the engine the existing cable runs thru some hard conduit , I used some electrical conduit here, about 300mm long, then just covered the rest in standard flexible wrap ) cable tie the new cable as often as you feel you need to.
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705063448_7083.jpg
Mount the fuse holder then join from the holder to the battery. Fit the fuse.
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705063802_55998.jpg
Voltage before the car is started
http://megashot.net/sbushinskii/mvc/photo_thmtitle/20150705063716_26095.jpg

Voltage with the car running.


I pulled the fuse and when the voltage dropped to about 11.7 volts the red battery light came on the dash.


Cheers Ean

[Ean Austral]

Done about 100ks and so far no issues , will be testing it out this weekend when I put it under some load with the fridge and a few other things.


I have read the D3 alternator is rated at 150 amps so I think 175amp fuse should be ample , but time will tell.


Cheers Ean

[drivesafe]

Hi Ean and sorry to be a wet blanket but when my TDV8 RR alternator went, it did not cause a total dead short, it just had a continuos 155 amp overload.

This will not blow your fuse but will still flatten the battery in a very short time. In as little as a few minutes if the battery is in a low state when the overload occurs.

The problem is not just the 155 amps being draw from battery by the alternator failure but there is also the additional 40+ amps still being draw by the vehicle's own electrical needs.

So when the alternator goes, there is at least a 200 amp load being applied to the battery, and no battery, regardless of size, can tolerate that sort of load for very long.

I am looking at a way to indicate that there is an abnormally low battery state but it's a way off yet.

Most vehicles will give some form of warning, usually via the battery light in the dash, but for some reason, most Land Rover alternator failures do not give any advanced warning and this is why they end up being such a dangerous failure.

[Ean Austral]

Hi Ean and sorry to be a wet blanket but when my TDV8 RR alternator went, it did not cause a total dead short, it just had a continuos 155 amp overload.

This will not blow your fuse but will still flatten the battery in a very short time. In as little as a few minutes if the battery is in a low state when the overload occurs.

The problem is not just the 155 amps being draw from battery by the alternator failure but there is also the additional 40+ amps still being draw by the vehicle's own electrical needs.

So when the alternator goes, there is at least a 200 amp load being applied to the battery, and no battery, regardless of size, can tolerate that sort of load for very long.

I am looking at a way to indicate that there is an abnormally low battery state but it's a way off yet.

Most vehicles will give some form of warning, usually via the battery light in the dash, but for some reason, most Land Rover alternator failures do not give any advanced warning and this is why they end up being such a dangerous failure.


No worries Tim,


its good to get another side of it, especially from someone in the trade. My simple brain tells me that the 175 amp fuse is to high , I would expect that 80% of the alternators capacity would be a more accurate size fuse.


Do you have an idea of what the amp output from the alternator under normal operation would be. If the Alternator is 150 amp would it normally run at 80amp and under extreme load be 120amp or what do you think.


I might invest in a few different size fuses and see if maybe a 125amp fuse keeps things running and if it blows its time to see whats going on.


I am still happy that I have done this, its just a matter of the right size fuse so if things do go wrong I get some warning not just a dead car in the middle of the road.


Cheers Ean

[Graeme]

Perhaps a 150A or even a 125A fuse would be more appropriate for a 150A alternator. I might try a 175A for my 3.0's 180A alternator.

[Ean Austral]

Perhaps a 150A or even a 125A fuse would be more appropriate for a 150A alternator. I might try a 175A for my 3.0's 180A alternator.


My thoughts as well Graeme. You would think any short above that will blow the fuse and atleast let you know its time to investigate.




Cheers Ean

[drivesafe]

Hi Ean and Graeme, unfortunately, a fuse is not the answer to the problem.

All automotive grade fuses are designed to carry their marked current for 4 hours.

But to achieve this, a fuse must be able to carry a higher current for a shorter period of time.

The amount of additional current that an AUTOMOTIVE grade fuse carries is set down in specific tolerances.

For example, the same automotive fuse must be able to carry 135% of its marked rate for around 30 minutes, and much higher currents for shorter time periods.

So your 125 amps fuse will carry around 170 amps for 30 minutes.

There is a reason for these higher than marked currents. When a DC motor is first started, it can cause a near dead short load of a micro second.

As such, all automotive fuses are designed to carry many times their marked rate for a few seconds, to compensate for such startup events.

Again, using my own experience, where my 140 amp alternator had turned into a 155 amp load, a 125 amp fuse would not blow for at least 35 to 40 minutes and no battery will tolerate the 200+ amp load for 15 minutes, and that is if the battery was in good condition and in a fully charged state, before the this sort of load was applied to it.

The best solution to give a warning with the way Land Rover alternators fail, is to have a current monitor that can detect both the current load, but more importantly, the direction the current is travelling.

So while the alternator is working as it should, as a power supply, and the current is travelling to the battery, all is well.

But if the alternator turns into a load and current starts to be drawn from the battery, you would get a warning in the cab.

This type of device would be easy to setup but is just too expensive.

[Graeme]

I must try to find out what size fuse is fitted to the Territory and also its alternator's rated output. However the reason for the Territory's fuse could be to prevent a fire if the alternator lead shorts to ground rather than the protect the battery against short-circuiting Zener diodes in the alternator.

I might have to try a 100A fuse to see if it blows with normal use.

[Graeme]

Littelfuse, who make the Mega fuse, state that at 200% of the rated load the Mega fuse will survive between 1 and 15 seconds. At 135% of the rated load the fuse will survive between 2 and 30 minutes, for which even the minimum time is too long. Hence it would appear that a fuse rated at half the alternator's rated output would be appropriate, ie 90A for a 180A 3.0 D4 alternator or 70A for a 140A D3 2.7 alternator. I might try a 100A fuse, being the closest without going too low. However whilst winching a higher rated fuse should be used due to the longer time at high current draw.

[drivesafe]

Hi Graeme and again, a fuse will not give you the battery protection you are after.

As you have found and as I posted earlier, the trip curve of a fuse ( and a circuit breaker ) means your battery will be discharged to a dead flat state ( usually down to around 7v ) before the fuse ever goes open circuit.

One alternative might be to fit a bank of high current diodes, in parallel, between the alternator and battery.

This would allow the current to flow from the alternator to the battery, when the alternator is operating correctly, but would block the current flowing in the other direction, if the alternator failed.

There are a number of potential issues with this setup though.

First would be whether the alternator would still get it's field excited if the main connection to the battery was blocked.

The second would be whether the voltage drop caused by the blocking diodes is corrected by the BMS.

If the BMS takes it's voltage reading from the battery voltage and not the alternator's output voltage ( as I suspect it does ) then there would be no voltage drop problem as the BMS would automatically correct the alternator's output voltage level.

All of this, be it fuse protection or diode protection, still does not give you an indication that something is wrong in the first place, until the battery is flat anyway.

[Graeme]

Is 15 seconds of 200A discharge going to flatten the battery?

[Ean Austral]

Tim,


What about a voltage indicator direct off the batteries , on my D2 I had a in-cab voltage reader that when the battery got to 11.5V it activated a beeper in the unit. I bought it for when we did the Canning Stock Route to keep an eye on the battery voltage in case we had an issue's with 2 fridge's running.


Is something like that the answer to this problem.


Cheers Ean

[Graeme]

For a warning to be of use firstly you would need to be able to stop quickly without endangering yourself or others and secondly disconnect the alternator whilst its drawing 150-200A all within 1 or 2 minutes, although a heavy duty switch might do the trick. I still think the 50% fuse is worth having.

[drivesafe]

Hi Ean and sorry I missed your question.

A voltage warning is what I am looking at as a substitute for a Current Direction Indicator.

While Graeme is partly correct, even with a low voltage warning, you are still going to have to act quickly.

But if you set the Voltage Warning for say 12.2v or even 12.0v, you will still have plenty of time to stop safely.

Then you can check to see if the voltage at the battery is still dropping once the motor is turned off and then be able to disconnect the battery or batteries.

If needed, you can do a quick disconnect by removing the NEGATIVES ( - ) off all batteries and then you can take your time to disconnect the alternator itself.

[drivesafe]

Hi Graeme, test it and see what you come up with.

The point is, to allow for normal operation of the alternator, the fuse still has to be larger than what is required to protect the battery from the a failed alternator overload.

For instance, it you fitted a 100 amp Manual Reset type circuit breaker ( a fuse is not really feasible in this type of situation ), it would tolerate 155 amps for about 1 to 2 minutes.

Not much time to draw high currents off the battery!

Add to the problem is that all of this is presuming the battery was in a fully charged state when the alternator failed.

There is a VERY good possibility that alternators are not charging properly, prior to their failure, so your battery is probably going to be in anything but a fully charged state at the time of the alternator failure.

There would be no problem with using such a low current CB providing you didn't have any extras drawing of your normal electrics.

But add an auxiliary battery and a set of driving lights and on a D3 you are not likely to trip a 100 amp circuit breaker because their alternator is flat-out at 140 amps.

However, in a D4, with these sorts of loads, you are likely to trip the CB in about 5 to 10 minutes. So you have to go to a higher rated CB and this then defeats the protection.

As posted above, a voltage monitoring system incorporating a low voltage warning, is a far more realistic means of protection and if you wanted to give yourself a quicker disconnect time, fit either battery switch or a 200 amp Manual Reset type circuit breaker, and use it as a switch.

[Graeme]

I'll replace my 200A fuse with a 100A manually resettable CB that incorporates a switch but then try 120A, 150A if the lower rated CBs trip in normal use. A friend had a few warnings of his D3 alternator's pending failure when some systems started to shut down but it still left him stranded in the middle of the road in busy traffic when it failed totally. I don't know how early the warnings occurred but even 30 seconds may allow a head-start on getting to the switch if one was fitted.

Even if the circuit breaker or manual switch doesn't save the battery then at least with a dedicated alternator cable the alternator can readily be disconnected and then switch over to the auxiliary battery or a fit temporary battery. This would allow the vehicle to be driven even if the battery has to be recharged via external means after quite short intervals. Disconnecting the original alternator cable is not a roadside task that I'd like to try, but would probably cut the cable from the starter cable at the starter motor if a suitable tool was on hand.

[drivesafe]

Disconnecting the original alternator cable is not a roadside task

Hence the suggestion of fitting a battery switch!

[Graeme]

But for the alternator, not the starter cable.

[Ean Austral]

I am currently running an 80amp fuse running a freezer and other stuff whilst out offroad and so far so good. I font have a winch so cant comment on how that will affect things. I have had the start battery at 11.8 volts and the other at 12 volts and started the car and charged up both batteries ok.

Will see how it continues to perform.

Cheers Ean

[ADMIRAL]

You have to be quick alright !! I had my alternator fail in the driveway while I was testing voltages. A puff of smoke and everything went black. By the time I got into the garage, grabbed a 10mm spanner and got a lead off the battery, it was sizzling. A quick check of the battery showed voltage was down to 5-6 volts. fearing the worst, but hoping for the best, I put in on a smart charger. It came up alright, but 2 months later, with colder weather, the battery is not up to starting the vehicle, and will not hold charge. The damage had been done in those seconds it took to get the lead off.

[Graeme]

I have a 120A resettable CB on its way although will try a 100A if the 120A doesn't trip with normal use. I preferred to not start too low to avoid having to either continually reset the CB or remove the CB if too frequent. Using a cheaper fuse to trial an appropriate value is probably the better path.

Alternators struggle to output enough current at idle so I doubt that the additional load of a winch is going to be satisfied by the alternator unless engine revs are increased.

[PhilipA]

Why wouldn't you fit a Schottky diode in the circuit to prevent back voltage.

I recall that I used some high amp diodes when I fitted an electric fan switch to my RRC to prevent the back voltage from switching the aircon on.

https://www.futureelectronics.com/en/diodes/schottky-diodes.aspx

The voltage drop should be compensated for by the ECU regulation of the battery voltage.
This is probably a stupid comment as I have no electronic qualifications , but I have used a diode to prevent back voltage successfully.

Regards Philip A

[Graeme]

If would be simple to determine if these alternators require battery voltage on the B+ cable for initial excitation. It would be feasible to also have a diode in the reverse direction with an in-line low current fuse if initial reverse feed was required. The high-current diode would need some form of cooling to dissipate a possible 100-125W. The voltage effect of inserting a diode could be measured at the battery if comparable conditions could be established, perhaps more difficult with the more sophisticated charging algorithms of D4s.

[Ean Austral]

I fitted a 70 amp waterproof resettable circuit breaker today in place of the fuse that I had installed. ( The 80 amp fuse was lasting about 6 weeks before it would blow ) , so will see what happens and keep an eye on it , I also found the 2 battery voltage monitor that I had in my D2 on the canning stock route trip , which is alarmed for 11.8 volts on each battery from memory so will also look at installing that, I may just use it on trips away, but will see how it looks and fits the D3.


Will update if it turns out that 70amp is not enough.


Cheers Ean

[Ean Austral]

I am having my doubts about 70 amp being enough , it has tripped 3 times since being installed , I will try a couple of things first but its 10 amps less than the fuse I had used.


Will see how things go over the next couple of days.


Cheers Ean

[drivesafe]

A few years back, I was looking at developing some specialised gear for motor home electrics.

While in the development stage, I purchased some high side current monitoring ICs.

I opted not to use them because they had a constant 35ma current draw and this was too much wasted power for the intended application.

But their power consumption is not a concern when they would only need to be operational while the motor was running, which would be the case for monitoring the operation of an alternator.

The Chips had two very useful features. The first was that they give a measurement in both directions, in this case, charging and discharging.

The other feature was that they did not contact the circuit being monitored.

In theory these chips, which are that small you could fit about 10 to 15 on your thumb nail, could be mounted on a thin strip of printed circuit board and secured to the alternator cable with a couple of small cable ties.

A small micro could then monitor the current flow and direction and give a warning in the cab.

The problem is that you still need a simple way to disconnect the alternator if a problem arose.

Just thinking out loud

[Graeme]

I am having my doubts about 70 amp being enough , it has tripped 3 times since being installedThe 120A CB that I fitted to the 3.0 D4's alternator hasn't tripped yet. Perhaps you might try a 100A.

[Ean Austral]

The 120A CB that I fitted to the 3.0 D4's alternator hasn't tripped yet. Perhaps you might try a 100A.


I had an 80amp fuse Graeme that lasted ok , , they never had any 80amp C/B in stock so I opted for 70 but I may have stuffed up.


Did you rubber mount yours ?


Cheers Ean

[Will Wallace]

I don't wish to hijack this but what sort of Kim's are the alternator's failing?

[Ean Austral]

I don't wish to hijack this but what sort of Kim's are the alternator's failing?


Seems to be random from what I have read, I just trying to avoid it killing my battery and leaving the car stranded in a very dangerous position. I know the car can easily drive with the battery not charging , I have driven it home from work a few times with it not charging.


There are a couple of threads on cars being stuck from a major alternator short, which flattens the battery in no time.


Cheers Ean

[Graeme]

Did you rubber mount yours ?No, just bolted in place.

[drivesafe]

I had an 80amp fuse Graeme that lasted ok , , they never had any 80amp C/B in stock so I opted for 70 but I may have stuffed up.

Hi Ean, also note that circuit breakers can be very temperature sensitive.

The higher the temperature, the lower the constant current capacity can become.

Is your CB mounted close to the motor?

If using a name brand, you should be able to check the operating specs for your CB.

[bee utey]

My suggestion for the day:

It's not the forward output current you're wanting to protect against but the reverse current. Therefore you could install as pair of diodes in the cable, one forward diode capable of carrying 100% of the output current and one reverse diode plus line fuse set to blow at around 20A or so of reverse current. That way the fuse will only see minimal current until a short occurs inside the alternator. The reverse diode is there to match the voltage drop across the forward diode so the fuse carries very little current under normal conditions.

[Ean Austral]

Hi Ean, also note that circuit breakers can be very temperature sensitive.

The higher the temperature, the lower the constant current capacity can become.

Is your CB mounted close to the motor?

If using a name brand, you should be able to check the operating specs for your CB.


Its mounted near the main start battery, between the battery box and the header tank. there is just a unused area there and its where I mounted the fuse.


I will have to see what the brand is and look it up, thanks.


Cheers Ean
Cheers Ean

[Ean Austral]

My suggestion for the day:

It's not the forward output current you're wanting to protect against but the reverse current. Therefore you could install as pair of diodes in the cable, one forward diode capable of carrying 100% of the output current and one reverse diode plus line fuse set to blow at around 20A or so of reverse current. That way the fuse will only see minimal current until a short occurs inside the alternator. The reverse diode is there to match the voltage drop across the forward diode so the fuse carries very little current under normal conditions.


I will have to some reading, as I know very little of the diodes you speak of.


I am just a would be if I could be mechanic so these things are off my radar . I am still think a spate cable for the alternator is a better idea than the original design but that's just my simple brain at work.


Thanks and Cheers Ean

[Ean Austral]

Well it seems 70amp is not enough. I put the 80 amp fuse back in and no issues , the 70 amp tripped faster the lower I let the battery voltage drop.




Cheers Ean

[bee utey]

I will have to some reading, as I know very little of the diodes you speak of.


I am just a would be if I could be mechanic so these things are off my radar . I am still think a spate cable for the alternator is a better idea than the original design but that's just my simple brain at work.


Thanks and Cheers Ean

Well to put it simply, a diode is to electrics what a spring loaded check valve is to a hydraulic circuit. It has a forwards voltage (equiv to opening pressure) and a reverse breakdown voltage that it can hold without conducting in reverse, like a max operating pressure. Symbol:

https://www.aulro.com/afvb/images/imported/2015/10/410.jpg

Current flows in the direction of the arrow (anode to cathode) but not the other way.

Now a handy arrangement of diodes suitable for this task is called a bridge rectifier, used to convert AC current into DC current. Any decent electronics shop should be able to sell you one and a suitable heat sink to bolt it to. Symbol:

https://www.aulro.com/afvb/images/imported/2015/10/411.jpg

If you connect your alternator output to terminals 2 and 4 together to double up the diodes, a battery connected to terminal 1 will get current. Now here's the magic trick: ALSO connect terminal 3, via a 20A fuse, to the battery at terminal 1. Now as you can see power can flow from the battery to the alternator in strictly limited quantities as needed. The rectifier will look something like this:

https://www.aulro.com/afvb/images/imported/2015/10/404.jpg

Ebay has them for under $20 from China. Example:

1200V 100A 1 Phase Rectangle Aluminum Heatsink Bridge Rectifier Diodes (http://www.ebay.com.au/itm/1200V-100A-1-Phase-Rectangle-Aluminum-Heatsink-Bridge-Rectifier-Diodes-/331660064857?hash=item4d387af859:g:w1oAAOSwQPlV~nx o)

[Ean Austral]

Thanks for that, our youngest daughter is an aircraft avionics tech, looks like a perfect job for her.

Cheers Ean

[Iain_B]

If you are looking for a means of disconnecting the alternator quickly, these work, but they are not cheap.

https://www.bluesea.com/products/7700/ML-RBS_Remote_Battery_Switch_with_Manual_Control_-_12V_DC_500A

A simple switch on the dash, or alternatively, link it to a low voltage alarm or Auber controller set to monitor battery voltage, if voltage is low, then RBS trips.

http://www.auberins.com/index.php'main_page=product_info&cPath=5_21&products_id=19

[Graeme]

1200V 100A 1 Phase Rectangle Aluminum Heatsink Bridge Rectifier Diodes (http://www.ebay.com.au/itm/1200V-100A-1-Phase-Rectangle-Aluminum-Heatsink-Bridge-Rectifier-Diodes-/331660064857?hash=item4d387af859:g:w1oAAOSwQPlV~nx o)A handy package and easy to connect a fuse-holder between pin 3 and pin 2/4 but one would want to monitor the battery voltage for a while to ensure that the 0.6V drop across the forward diodes didn't unduly lower the charge voltage at the battery as the regulator in the alternator is seeing the full o/p voltage.

[drivesafe]

https://www.aulro.com/afvb/images/imported/2015/10/404.jpg

Ebay has them for under $20 from China. Example:

Hi bee_utey, that is a very clever idea but I suspect that device is not large enough, both in the heatsink size and the current capacity.

The unit is designed as a bridge rectifier and as such is actually only capable of handling 100 amps pre diode for a very short time during each AC phase cycle.

To do what is required in this situation, even with an 80 amp draw, the diodes will need to handle a continuos forward current load of 40 amps, and dissipate a hell of a lot of heat.

Furthermore, the connection tabs are WAY too small.

A 200 or better still, a 300 amp version, if available, would be much better and you could still set it up the way you described.

Again, a very clever idea.

[Will Wallace]

Does anyone have a part number for the diode pack so I can do it over Christmas?

[drivesafe]

This may be the answer to the dangerous alternator failure situations.

Sterling Power Australasia | Advanced Marine and Automotive Power Products (http://sterling-power-australasia.com/product/current-limiting-vsr-pro-con-cvsr/)

Sterling Power Australasia | Advanced Marine and Automotive Power Products (http://sterling-power-australasia.com/product/current-limiting-vsr-pro-con-cvsr/)

I have just received a 210 amp unit last week and will, when I get a chance, carryout some testing to see if it will give the protection needed.