Smart alternator

[Mike DiD]

. . . When the engine is running, this would be the alternator for sure, but as to where the earth return goes, I wouldn't be able to guess. . . . .

Guessing ia waste of time. If the current has come FROM the Alternator, it MUST return to the Alternator.

[Mike DiD]

. . . In my case, the power for the trailer comes direct from the positive battery pole (via a fuse of course) and the trailer socket on the car is earthed to the body adjacent to the socket. How it gets from there back to the battery/alternator, I don't know, but it flows through the body shell and all the spot welds. Eventually it returns to the battery via the battery earth strap. . . . .

There is a heavy wire from the Alternator direct to the Battery, so the current flows from the Alternator to the Battery +ve post, through your wiring to the socket. Back the Earth in the socket to the Body, through the body, the heavy Body to engine wire, then through the engine block to the case of the Alternator.

[Mike DiD]

. . . I suspect that the earth sensor wire of the alternator would be taken from the earth terminal itself, rather than the engine block or elsewhere. In this way, any current draw to any circuit will be sensed by the current sensor on the earth terminal, and the alternator can then adjust its output accordingly. I doubt that the electronics of the alternator would be earthed via the alternator body because this would confuse the earth return current sensor.

There is NO Alternator Current Sensor, because there is no point in doing that. To control battery charging, you have to sense current flowing through the BATTERY ONLY - not the total current being drawn by Battery and all other loads in the vehicle.

Have a look at the front of the Battery, you can see the black square Hall Effect Current Sensor around the Battery to Body Lead - because that lead ONLY has current flowing THROUGH The battery.

Have a look at the Pajero Wiring Diagram - there is no separate Alternator Earth wire. If there were, it would have to be the same diameter as the Alternator Positive Output lead.

[Paul NT]

The issue of smart alternators is intriguing, the voltage being controlled by the vehicle's computer rather than a voltage regulator built into the alternator. But does any one know if the Pajero has regenerative braking technology, like Mazda use in their 3 & 6, and lots of European cars? I have overcome the issue so far by solar panels assisting charging auxiliary batteries via a mppt.

[Keithyv]

The issue of smart alternators is intriguing, the voltage being controlled by the vehicle's computer rather than a voltage regulator built into the alternator. But does any one know if the Pajero has regenerative braking technology, like Mazda use in their 3 & 6, and lots of European cars? I have overcome the issue so far by solar panels assisting charging auxiliary batteries via a mppt.

LOL Pajero with regenerative braking, that's a funny one..

[nj swb]

But does any one know if the Pajero has regenerative braking technology, like Mazda use in their 3 & 6, and lots of European cars?

No, it does not.

[Radios]

In my NX I run two batteries and use the Redarc voltage sensing relay. Despite people saying this relay will not work with a smart alternator I have no problem. On idle at start up I get around 13.4 volts at idle and when running it gets up to 14.2 and slowly goes back to 13.8 when the batteries get charged. First starting battery lasted 4 years. When I run the fridge in the van which draws 23 amps the same occurs

[Dicko1]

In my NX I run two batteries and use the Redarc voltage sensing relay. Despite people saying this relay will not work with a smart alternator I have no problem. On idle at start up I get around 13.4 volts at idle and when running it gets up to 14.2 and slowly goes back to 13.8 when the batteries get charged. First starting battery lasted 4 years. When I run the fridge in the van which draws 23 amps the same occurs

What do you mean draws 23 amps ?

[Mundy55]

..... Despite people saying this relay will not work with a smart alternator I have no problem. ....

Not everyone says this. What they say is at 13.2 volts charging current, AGM or wet cell batteries will be charged eventually. Fully charged battery voltage is 12.7 volts and a deeply discharged battery will have a voltage of around 11 volts. The voltage of the charging battery increases as it charges, ultimately getting to 12.7 volts. This gives a charging voltage differential of between 2.2 and 0.5 volts. A DCDC charger will typically maintain voltage of 14.7 or so, giving a charging differential of between 3.7 and 2 volts, giving a much faster full charge. A DCDC charger will also typically control the initial charge current to a deeply discharged battery to ensure its not charged too fast and will also maintain the correct float voltage, both extending battery life.

However, calcium batteries require a higher charge voltage to be fully charged and that may not occur will a smart alternator without a DCDC controller.

So, whether you need a DCDC charger depends on how you drive and camp. If you do short hops between camps (say 2 hours or less) then the second battery probably won't have time for a full charge without a DCDC charger. However if you drive for more than 4 or 5 hours per day, it may do so.

[Radios]

The 3 way 190 ltr fridge draws 23 amps when running on 12 volts. I use very heavy cable from the 2nd battery to the fridge

[Dicko1]

The 3 way 190 ltr fridge draws 23 amps when running on 12 volts. I use very heavy cable from the 2nd battery to the fridge

Thought that might have been the case. 3 way fridges are ridiculous to run from batteries unless your constantly feeding charge into the batteries and have a good battery bank.....pulling over on the side of the road and doing a couple of hours shopping would see a 105amp/hr agm well past its 50% longevity life. Mate pulled his out of his junko camper and put a waeco 12/240 volt in its place

[Mundy55]

Thought that might have been the case. 3 way fridges are ridiculous to run from batteries unless your constantly feeding charge into the batteries and have a good battery bank.....pulling over on the side of the road and doing a couple of hours shopping would see a 105amp/hr agm well past its 50% longevity life. Mate pulled his out of his junko camper and put a waeco 12/240 volt in its place

2 points re above. Whilst it may draw 23amps when running, a 3 way fridge already to temp doesn't run all the time so it won't consume 46Ahrs over a 2 hour period.

Secondly, most, if not all, van installation instructions say the 12volt supply to the fridge van should be via an ignition operated solenoid so it doesn't flatten the battery when the car engine is not running. If you have a 190L fridge, whether it be 12/240V or 3 way, its going to draw a lot of amps when running.

[RUGGA]

Whilst it may draw 23amps when running, a 3 way fridge already to temp doesn't run all the time so it won't consume 46Ahrs over a 2 hour period..

Yes it will unfortunately, 12v on a 3 way fridge does not operate via a thermostat - just constant draw regardless of internal pre chilled temp.

[Mundy55]

Yes it will unfortunately, 12v on a 3 way fridge does not operate via a thermostat - just constant draw regardless of internal pre chilled temp.

Thanks, you are correct, up to a point and I concede my sloppy description is the major culprit. Arguably its also not relevant to the major thrust of Dreamerman's thread intent.

I agree that my 3 way fridge (93L), for example, doesn't have a thermostat per se but it does have a "cooling effort" controller, which I presume means the fridge runs continuously and the controller throttles the current draw. So, once up to temperature, I run on about 50% to 70% (depends on ambient temp), otherwise I freeze the vegetables. As far as I can tell, it seems to draw about 10A.

If not on that basis, then it runs on a time on/time off arrangement. Thus, I assume, at the maximum operation point it would run continuously and at lowest point it would run on a much less time basis. The overall effect is the same in terms of Ahr consumed over time.

It would be good to know how the typical 3 way fridge controller works. It would also be great if the fridge did have a thermostat so I didn't have to guess what the ambient temperature was going to do over the next half day so I didn't have a fridge too warm or too cold.

[Radios]

I know it is going off topic however all interesting. While traveling when we pull up for a stop I always turn the fridge over to gas then stop the engine and when ready to go start I was intent not to use a relay to minimize voltage drop which is the most common complaint when running 3 way fridges on 12 volt. Never had any trouble wiith freezing veges on 12 volt