Need more power

[E_T_V]

Does anyone know if I can uprate the alternator on the diesel engine?

The manual strangely gives its max output as 65 amps at 6000rpm, but the diesel engines max out at 4,500..

Any ideas would be helpful

Thanks

Daniel

[tony]

why have you got a charging problem?

[E_T_V]

Not yet no, but I bet I will have when I'm finished rewiring the camper, so I thought I'd ask in advance.

[derek mclean]

I don't think you need to worry about the abilities of a 65A alternator.
If you are going to use ancillaries in a camper the best plan is to rig a second battery, and use this to work the ancillaries. Use an isolator so you can disconnect it from the main battery when static, and connect it when moving. Or just use croc. clips to do the same thing.
Alternatively, carry a spare battery and jump leads for starting in the morning. But if you're careful you shouldn't flatten a decent battery with a few hours of radio and a couple of 8W fluorescents. A fridge would be a different story. They seem to take a lot of charge out of a battery overnight. Best to use gas when static.
In any case an uprated alt. won't help when the engine isn't running, so a second battery, either connected in or not, is the only way to ensure you can use your interior bits and still be able to start it up in the morning.
If you want more detail on how to rig it, just shout. I can give you chapter and verse if you really need it.

Derek.

[E_T_V]

No that isn't the problem, I'm gonna do the whole leisure battery split charge relay etc for the camper but I want some extra juice available for the extra lights etc. (if you reckon it will probably develop half of its rated output in "normal" use then that is only about 400watts, not a lot to play with really.

Apparently the police alternator is different from the standard one? anyone know anything about it?

[e692wtt]

Dynamos have a roughly 'linear output', ie they produce an output of current related to the speed of dynamo rotation (eg at 4000rpm they will produce roughly twice the output when running at 2000rpm).

Alternators are different, they produce most of their available output from low speeds of rotation quite unlike a dynamo, and that's why they replace dynamos in cars. Even so, car batteries on alternator-equipped cars can still benefit from an occasional external charging-up in winter when the car is used for short journeys at low speeds - but nowhere near as many as on a dynamo-equipped car!

I'd expect your alternator to produce well, well over half its 'rated output' in normal use, and wouldn't worry. If there is a problem at a later date then change the alternator, but I would expect this not to be really necessary unless you go for overkill on the extra lights.

[derek mclean]

Yes, I agree with Rich, you should have no worries with a 65A alternator.
65A at 12V = 780W, which is more than enough to cope with any number of lights that you might want to fit on your van.

There are two issues. One is the use of some power when static, and you are addressing this. The other is what happens when you are moving, and rally cars have been driving around for many years with ordinary alternators powering headlights and spotlights. You would need to have about ten spotlights to overload your alternator. How many lighhts do you propose to have.

I think the maximum power rating of the alternator that you quoted as 6000 rpm is actually at an alternator speed of 6000, not engine revs. They usually do a higher speed than the engine, and can be taken to 15000, although they rarely do this. Usually the alternator will be geared to be about double engine speed. So to achieve the maximum power speed of 6000 the engine will be doing about 3000. And even at 2000 it will probably be capable of generating 40A. So, as I said, no worries!!

Hope this helps reassure you.

Derek.

[tony]

dont ask me why i know this but a alternator runs at seven and a half time that of the engine speed:) p.s.output voltage is around 13.5-13.8 volts depending on the load

[E_T_V]

I was thinking of beefing it up (like the police issues ones did) becuase:

1. It will have to charge 2 batteries in the camper
2. It is gonna have lots of electrical goodies in it
3. I like to be able to see in the dark as my avatar suggests :D Remember 800W is only your headlights a lightbar and some fog lights with nothing left over to charge your battery, heat the car etc.

[derek mclean]

Thanks, Tony. Yes, I was a little imprecise in using the nominal 12V for calculations. The actual system voltage with the engine running should be 13.6 to 14.4, ideally. This would make a slight difference to the calculations. But in fact bulb ratings are generally based on 12V, I believe, so it is all a bit confusing, so I won't bother to try and get it right. Siffice to say that a 55W bulb draws about 5A.

As for the assertion that alternators run at 7.5 x crankshaft speed, this is clearly nonsense in a general way. Some low-revving large diesels may have such a ratio, but most car engines (petrol or diesel) have a ratio of about 2 to 3, so that the alternator will reach its maximum speed way beyond the normal range of the crankshaft. If an engine is capable of doing 7000 (even although it may never reach that in normal conditions) it would have a ratio of about 2, to prevent over-revving of the alternator.

And if you, ETV, are going to have so many lights on that you are likely to overload a 65A alternator, then you are risking serious accusations of anti-social behaviour. Battery charging doesn't take a lot of alternator power, at least not on a long-term basis. Even a second battery well-used overnight will not take more than about 10A for very long. And the standard battery will take about 20-30A for a few seconds after starting, then drop to about 5A for a few more minutes, unless you have a starting problem too and will draw a lot of charge from the battery in the attempt.

Even a high load switched on after a short time will still allow the batteries to recover, albeit a bit more slowly. But if you are going to flatten a leisure battery overnight and start your engine in the morning, then switch on ten 55W lights within a very short time, then I give up trying to help you, because you are beyond help.

Any electrical modifications require a bit of common sense to help decide how and when to use them, i.e. not all at the same time. Common sense will tell anybody that 65A is more than enough to supply normal lighting, a bit more lighting, and split charging too. Uprate it if you want, but why bother? It will just cost you more money, needlessly.

Incidentally, a split charge system is subject to various problems and is unnecessarily complex. My suggestion of a switch or a pair of clips actually works better and is cheaper too. I have been using a high-current isolator and starter cable to join two batteries in a breakdown van for many years. It is much better than relays, and it can be left connected most of the time. In your case a smaller switch would be adequate. I would suggest a 30A switch, and would expect the maximum load to be less than this, and not on for a long time.

What other electrical load are you planning? Even a high-powered stereo won't take more than a few amps. A fridge takes a few. Are you adding electric power steering? That might explain your concerns! No, I still think you are panicking too much. But if you care to tell me exactly what "goodies" you think will be too much for it I will try and help, if I can.

Derek.

[E_T_V]

(snip)
And if you, ETV, are going to have so many lights on that you are likely to overload a 65A alternator, then you are risking serious accusations of anti-social behaviour. Battery charging doesn't take a lot of alternator power, at least not on a long-term basis. Even a second battery well-used overnight will not take more than about 10A for very long. And the standard battery will take about 20-30A for a few seconds after starting, then drop to about 5A for a few more minutes, unless you have a starting problem too and will draw a lot of charge from the battery in the attempt.

Even a high load switched on after a short time will still allow the batteries to recover, albeit a bit more slowly. But if you are going to flatten a leisure battery overnight and start your engine in the morning, then switch on ten 55W lights within a very short time, then I give up trying to help you, because you are beyond help.
(snip)

Derek.

Antisocial behaviour is a bit strong isn't it? And I don't believe I'm beyond help, as that was why I was asking the forum members for any advice. I'd like to point out that I only use fog lights in conditions of reduced visability or only with main beam headlamps and none of them cause undue dazzle, and that your assumptions are based upon 55w bulbs rather than 100w+ ones which may be used in driving lights.

I was only asking if it was possible or anyone had done it as it seems the police considered it a necessary upgrade for their vehicles? For instance if a rover 800 alternator happened to fit which had a bigger capacity then I could look out for one in scrapyards etc.

Picture the scenario, it is a freezing cold murky wet morning and I have to leave early to travel a significant distance before sunrise (a scenario I'm likely to have a lot of very soon unfortunatly). The heater is on (20 amps), the wipers (5amps), the rear screen demist (20 amps), headlights (10 amps), fridge/stereo/inverter/etc (5 amps), fog lights (10 amps). I'm over my amps budget already and that is without any battery charging of the car or the leisure battery.

I thought it wise to ask the question before I encountered any problems.

As for the split charge system it isn't complicated at all just a relay that is energized by the alternator when the engine is running allowing the leisure battery and leisure items to draw power from the engine.

[Simon]

Standard fit Rover 800 2.0 litre item was 65A (A127) Models with air conditioning had an 80A alternator but as its an A133 it might not fit. On the camper have you considered a small 3 way fridge, and are you considering mains hook-up?

[derek mclean]

Now that you have explained the problem more fully I understand.

I don't think a heater motor takes 20A, even on full speed. I would need to check to be sure, but I am fairly confident it doesn't. But I would simply run it at a lower speed once the engine warms up.

And the HRW should be turned off after it has done its job. This is what I mean by common sense. Most MMM cars have a timer on the HRW. The one on my M16 Monty has an infuriatingly short timer.

I don't think 100W bulbs are legal! And I don't believe such a high output is necessary on a camper anyway. Even a rally car can cope with 55W spots (just two of them at that).

Are you going to be doing a lot of winter camping then? Even if you are, you are unlikely to need to use all these things within a very short time of starting your engine. The time you spend exiting the camp site will provide most of the battery recovery requirement, and then there will be enough to supply more lights than you could possibly need. And heater, wipers and radio.

I believe the point I am trying to make is that you are very unlikely to have all these things on at the same time. Even if you do, the battery can cope with this scenario on a short-term basis. That is one of its functions, to store energy when it is available and then give it up again when it is needed.

I still maintain that you will not need to uprate the alternator. The police would be using beacons, radios, sirens, alternating headlights, etc. and they always want maximum reliability, despite moron drivers. It is my belief that we mere mortals don't need such
a belt and braces approach. But, as I said, if it makes you feel happier to fit a bigger alternator, who am I to stop you?

As for what else may fit, I am afraid that is another matter that I can't answer. Trial and error, I fear.

Sorry if I got a little bit abusive. Maybe if you had listed the load earlier I would have been able to be more constructive.

Hope this finally settles the matter.

Derek.