Alternator Capacity

[640Newton]

Could someone please educate me on how much power the alternator on a TDV8 RRS can generate? How do I know if I am putting too much load on the alternator?

• I have a dual battery fitted to the RRS - so it's charging two batteries in the car.
• I have an Engel 40L compressor fridge in the boot - so it's running that.
• I have a UFH radio installed - so it's running that.
• I tow an camper trailer that has dual 105Ah deep cycle batteries being charged via an Anderson plug (the camper has a CTEK XS15000 charger) - so it's charging that.
• Sometimes my daughter likes to watch a DVD in the back - so it's running that.
• At various times we'll be charging phones, iPods etc etc.

How much can the alternator handle?

[Doctor W]

Could someone please educate me on how much power the alternator on a TDV8 RRS can generate? How do I know if I am putting too much load on the alternator?

• I have a dual battery fitted to the RRS - so it's charging two batteries in the car.
• I have an Engel 40L compressor fridge in the boot - so it's running that.
• I have a UFH radio installed - so it's running that.
• I tow an camper trailer that has dual 105Ah deep cycle batteries being charged via an Anderson plug (the camper has a CTEK XS15000 charger) - so it's charging that.
• Sometimes my daughter likes to watch a DVD in the back - so it's running that.
• At various times we'll be charging phones, iPods etc etc.

How much can the alternator handle?

I'm sorry that I can't give you a figure for the max. output rating of a RRS TDV8, it may be different for the Luxury model ( more electrical equipment), but I feel pretty safe in saying you're nowhere near its maximum draw....

The maximum output would be well in excess of 100 Amps, more in the mid-range between 100 and 200 Amps as a minimum I would think.

[640Newton]

Thanks Doctor W, that's what I was hoping to hear. I want to add two rear cameras, one for the car and one on the back of the camper trailer, but before I do it I wanted to make sure it didn't have further implications from a power point of view.

[drivesafe]

Hi newton, I’m not sure of the exact size alternator you have in the RRS, but it will either be the 140 or the 180 amp alternator.

In either case, you can not overload an alternator so it doesn’t matter how many or what size batteries you have and how low they are when charging them while driving.

Even with other accessories and a few driving lights thrown in, if you apply a current load higher than your alternator’s maximum output at that time, the alternator’s output voltage drops.

As voltage drops, so does the maximum current being applied to the alternator. Eventually, as the voltage continues to drop, the amount of current being applied equals the maximum the alternator can produce so the voltage stabilises.

As all your batteries charge, the current demand reduces and as such, the alternator voltage increases until the voltage rises back to it’s normal operating level.

So theoretically, you can add as much load as you need and your alternator adjusts it’s charging to accommodate the loads being applied to it.

[Blknight.aus]

the only time that becomes a problem is when your battery charging requirement drops the voltage output to below 10.5V and that shuts the ECU down.

IF you're dumb enough to let that many expensive batteries get that flat then best you install one of drivesafes management systems first. the later systems are not dumb as a post like the ones I knock in for about $30 (and I wouldnt install one on anything of better tech than a D1 Maybe a td5 deefer) and will drop off the aux charging when the main battery voltage drops too low That keeps the main battery alive, the ecu happy and the engine running till the alternator charges the main battery up and then it starts all over again untill theres enough oomph in the aux batteries to not suck the guts out of an alternator.

I did the cape with a 35A alternator running 2x n70ZZ an old engle fridge, UHF, car radio, charging a GPS phone, running up to 3 fuel pumps, driving my inverter occasionally and the mother of all 12v compressors as required I only needed to be tow started once due to dead batteries and that was because my glow plug relay welded itself shut and put a 90A draw on the batteries that I didnt work out till the next day when the batteries were down to about 4v.

[Wilbur]

DVD players, rear view cameras, GPS's, phone and camera chargers etc take absolutely stuff-all power from the battery or alernator. Any item that can be run portable with a carry-around battery will be virtually invisible to a car electric system.

Fit as many such gadgets as you want and there will be no problem.

The possible problem could be if all three auxiliary batteries are low in charge there will be a high current drawn from the alernator when the engine is started up, and this could go on for some time until the batteries are at least partially charged.

I don't know about modern alternators, but those fitted a few years ago would have their lives shortened considerably by this constant overload. I expect most of todays would also. I would be very surprised if the current rating is a continous rating, more likely a peak rating.

The very best thing you can do is to get a C-tek, Redarc, GSM or similar DC to DC convertor that will give you proper three stage charging for your 'house' batteries and limit the current that can be drawn from the alternator. The batteries will become more fully charged (by a BIG amount) and your alternator will be safe.

Cheers,

Paul

[drivesafe]

Hi Wilbur and sorry but that is absolute crap, put out by sellers of this junk as a means to try to justify why unsuspecting potential customers should part with large sums of hard earned money to buy something that does not work anywhere near as well as your good old alternator.

Furthermore in Newton’s case, with the number of batteries he has, one of these DC-DC devices would actually cause his batteries to be in a much, MUCH low charged state at the end of a days drive than what his alternator can charge them to.

These DC-DC devices can fully charge batteries but in almost every case, they require a much longer driving time to do so and when an alternator can do it better and in a shorter drive time and for a much lower initial set up cost, why would anyone want to waste time and money on a system that will not only take longer to charge batteries but will ultimately end up shortening the batteries life span.

One more point, it takes a VERY long time for constant high current loads to have any effect on an alternators operating life span and this includes old versions. You would need to drive all day every day over a long period of time with a constant high current before an alternator would fail.

[Blknight.aus]

I'll back drivesafe on that...

The only time I can think of that even a half aware tourer would want to setup one of those DC-DC chargers is

a, when hes got 240 plug in charging fitted to the tow vehicle and he never disconnects the trailer from the tractor

b, when hes got a trailer battery configuration that is higher voltage than the tractor (and even then Id still be trying to con him into fitting a seperate alternator)

[Wilbur]

Hi Wilbur and sorry but that is absolute crap, put out by sellers of this junk as a means to try to justify why unsuspecting potential customers should part with large sums of hard earned money to buy something that does not work anywhere near as well as your good old alternator.

Furthermore in Newton’s case, with the number of batteries he has, one of these DC-DC devices would actually cause his batteries to be in a much, MUCH low charged state at the end of a days drive than what his alternator can charge them to.

These DC-DC devices can fully charge batteries but in almost every case, they require a much longer driving time to do so and when an alternator can do it better and in a shorter drive time and for a much lower initial set up cost, why would anyone want to waste time and money on a system that will not only take longer to charge batteries but will ultimately end up shortening the batteries life span.

One more point, it takes a VERY long time for constant high current loads to have any effect on an alternators operating life span and this includes old versions. You would need to drive all day every day over a long period of time with a constant high current before an alternator would fail.

Yeah well, Hi Drivesafe, I am sorry too, but what I wrote was not crap. I fully support your right to be the expert, but nonetheless I will justify what I wrote.

1. The very best deep cycle batteries still have greatly shortened life span if discharged below 50%. Some AGM makers claim better, but they have not been justified yet.
2. Unless the house batteries are EXACTLY the same chemistry as the car battery and alternator are set up for, AND there is absolutely NO loss in the leads between the car battery or alternator and the house battery, the house battery will seldom get beyond a 70~80% charge level.
3. Assuming that one wants full life span out of the house battery and so will only discharge to 50%, then because one is only charging to 75% one can only use about 25% of the batteries capacity. Thus your 100 amp hour battery is good for 25 amp hours for example.
4. Fitting a proper three stage charger will allow the batteries to charge to close to 100%, even if there is loss from the leads between the alternator and the DC-DC charger.
5. You are quite right, in Newtons case, the DC - DC chargers I mentioned are all relatively low current devices, around 25 amps. At start-up, with the batteries well discharged, there will INITIALLY be a very high charge current when fed direct from the alternator. However, after a very short time that charge current, even for two 100 amp-hour batteries, will drop well below the 25 or so amps that the DC-DC convertors will supply. This will happen because the voltage is not high enough to allow the batteries to draw that much current once they begin to take on a surface charge. The DC-DC convertors give the extra voltage that allows the batteries to continue to take charge after their initial savage hunger is satisfied.
6. Anyone with an amp gauge in their vehicle can prove this to themselves. With the engine stopped, switch on your heqadlights for about a quarter of an hour, turn them off and start the engine. Note the very high charge current, which after a few minutes drops right back to a low level.

I fully accept your right to be the expert, you certainly do have the points on the board, but by a hasty reply to my post you have decimated the important part of what I wrote - that is, that low power devices can be used as much as one wishes without any risk to the car battery system. That really was the thrust of the original question.

No offence meant, and lets all still be friends.

Cheers,

Paul

[Wilbur]

I'll back drivesafe on that...

The only time I can think of that even a half aware tourer would want to setup one of those DC-DC chargers is

a, when hes got 240 plug in charging fitted to the tow vehicle and he never disconnects the trailer from the tractor

b, when hes got a trailer battery configuration that is higher voltage than the tractor (and even then Id still be trying to con him into fitting a seperate alternator)

Hi Blknight,

Well I'll back myself....

a, If he is relying on a 240 volt charging system, the dc-dc system vs alternator direct is completely irrelevant.

b, yes, a separate alternator would be ideal PROVIDED the alternator was matched to the battery chemistry AND that there were no appreciable losses in the leads. If either or both of these are untrue, then the DC -DC alternative would fix the problem.

Cheers,

Paul