Club 80-90 Forums

Several of us were chatting at VF about the merits of fitting a larger a/h alternator. Can someone enlighten us please?

charges your battery/batterys faster, plus some standard fit alt's are very low ie 40amp, and your trying to charge say a 75amp starter and 110 amp les battery!

jamesc76 wrote:charges your battery/batterys faster, plus some standard fit alt's are very low ie 40amp, and your trying to charge say a 75amp starter and 110 amp les battery!

Thanks James, thats sort of the way the discussion went. For example the standard alternator on my van is 45 a/h where as my starter battery I think is 60 and then leisure is 70 I think. So faster charging is the only advantage?

Bear in mind that if you are asking a larger alternator to provide more amps to your battery and large current accessories (head lamps, heater fan, radiator fan, fridge, heated window, wipers etc each of which draw 8-10 amps) it will draw more mechanical energy from your engine.

To do this it will create more tension in the drive belt. So, if you have the original V-belt drive and worn pulleys you could well end up with belt slippage and further increased wear plus noise. Increased tension will also put more load on the pulley bearings at the alternator and water pump leading to increased wear. Later vehicles with big alternators usually have the flat belt drives to allow for this.

Not saying you can't do it but just consider if you also need new pulleys and belt. Also think about the thickness of the wires from the alternator to the battery.

Garyd

some interesting thoughts there Gary.

You are looking at the duty cycle of the alternator, if you have a 45A alternator and you are using it to charge your big battery it will run at a higher duty cycle (ie harder for longer) than a larger alternator on the same battery.

look in mercs and beemers from the same vintage, the bigger the engine the bigger the alternator.

Mine was a standard 45ah which I swapped for a 90ah. Other than needing a slightly longer belt (1100 instead of a 1050) I've had no other issues at all. Just really happy batteries!

I am running a standard 90 amp alternator and a Sterling Alternator manager.

This clever device works out what the leisure batts and the starter battery need, and tell the alternator what to output. This works absolutely perfectly. The system can put out over 100 amps at 14.8 volts.

Increasing the size of your alternator will make almost no difference at all. The way the alternator works is that the field windings detect the voltage in the alternator output, the lower the voltage the higher the amperage output. This works ok in normal one battery situations as when there is high demand on the battery it lowers the voltage. The problem with leisure batteries is that they are connected in line, and even if the leisure battery is really flat it does not draw enough amps from the main starter system to get the alternator to boost the output. If your starter battery is at 13.6v and your leisure battery is flat at 12.2 volts the alternator will just see the 13.6v of the starter battery and not boost for the leisure bat.

The Sterling gets around this by accurately measuring both starter and leisure battery and then controlling the alternator field windings to give a desired output. The higher the amps it wants the more it lowers the voltage in the field windings, the Sterling unit then amplifies the voltage up to 14.8v which is a bulk charging voltage.

Leisure batts never get charged incampers in my expeience no matter what alternator or split charge relay you use.

Here is the unit.


Here is the alternator with 25mm wire and temp sensor.


The two 75 amp hr batts, now 3 years old.


The control panel showing 113 amps output at the alternator at 13 volts and 105 amps at 14.5 amps going into the leisure batts, now thats gonna charge them quick.

Have used this system for 3 years now, and it has been faultless.

Makes free camping so easy with lots of batt power, and a quick charge time in the morning.

It's not cheap though.

If I were doing this again, and not wanting to spend 400 quid then I would get the heaviest duty switch-over relay, and wire the batteries up with good thick cable. This way a flat leisure battery will have a greater effect on the starter battery circuiut, and lower the voltage enough to increase the output. Standard relays and speaker wire are never ever going to charge a leisure battery what ever the alternator.

Concentrate on a high quality, high amperage switch over relay and fat wires, the alternator will be fine.

All valid and good points....I will add....simple maths.

Original van back in the 80's with very few consumers and it's original 45ah alternator...... happy as larrie!
Same van 25 years on but now retro-fitted with a powerful stereo and amp, converted to a full camper with interior lamps, propex heating, project 2 lights .....in other words: with everything turned on, the charge amps from the small 45ah alternator is being exceeded by discharge amps possibly resulting in a flat battery (under worst conditions).

Martin

more thoughts...
A higher rated alternator will draw more load on the engine as said, when charging a nearly discharged battery. The belt tension adjustment should be the same regardless of the size of the alternator. Over tensioning a belt is never a good idea.

Alternators are designed for maintaining charged batteries. They should last quite long doing this task. It is never a good idea to ask an alternator to recharge a near to flat battery, but we do it all of the time. Realize that this severe "duty cycle" can wear the alternator out before it's time...

The more electrical energy used by vehicle, the bigger the alternator to supply it. Battery/batteries are for when engine is not running. Quad headlights, driving lamps, electric fuel pump, wipers, heater fan, engine computer, heated windows, electric windows, etc can easily add up to 40-60 amps... add at stereo amp and sub and it can easily be over 60 amps. Battery ratings mean nothing to alternator... Battery rating is for amount of energy stored in battery. Most batteries should not be charged with more then 20 amps. Now if you have 2 or 3 batteries, then you can use 40-60 amps just recharging batteries plus whatever is on in vehicle. Alternator rating is for amount of maximum energy it can produce... and keep in mind alternator rating of 90 amp will only produce 90 amp for a short time as when they work hard the get hot... and when they get hot they put out less amps... usually about 70% at best of rating.

Leisure batts never get charged incampers in my expeience no matter what alternator or split charge relay you use.

I have to disagree with you on that.

My 90A alternator charges both my main and leisure battery up, even when I have lights, stereo, fridge and fan on.
The leisure battery gets between 13.3 and 13.8v going into it, subject to what goodies I have running.

eatcustard wrote:

Leisure batts never get charged incampers in my expeience no matter what alternator or split charge relay you use.

I have to disagree with you on that.

My 90A alternator charges both my main and leisure battery up, even when I have lights, stereo, fridge and fan on.
The leisure battery gets between 13.3 and 13.8v going into it, subject to what goodies I have running.

I agree. I find that a short run in my motor charges up the leisure battery perfectly to the green zone. What I do find strange is that if I use electric hook up, the on board battery charger on my westie only seems to charge the starter battery and the leisure battery charge light remains at yellow rather than the maximum green. Is that normal? Who knows. However, having said that this has never caused me a problem.
Patrick

The BBB is dual output on a Westie and should charge both.

Martin

lloyd wrote:The more electrical energy used by vehicle, the bigger the alternator to supply it. Battery/batteries are for when engine is not running. Quad headlights, driving lamps, electric fuel pump, wipers, heater fan, engine computer, heated windows, electric windows, etc can easily add up to 40-60 amps... add at stereo amp and sub and it can easily be over 60 amps. Battery ratings mean nothing to alternator... Battery rating is for amount of energy stored in battery. Most batteries should not be charged with more then 20 amps. Now if you have 2 or 3 batteries, then you can use 40-60 amps just recharging batteries plus whatever is on in vehicle. Alternator rating is for amount of maximum energy it can produce... and keep in mind alternator rating of 90 amp will only produce 90 amp for a short time as when they work hard the get hot... and when they get hot they put out less amps... usually about 70% at best of rating.

The Sterling system I have bulk charges the batteries, and monitors the batteries internal temp via the battery posts. Even when charging at 100 amps and 14.8 volts the battery temp has never got more than 5 degrees C over ambient. The batteries are 3 years old now, and just regular lead/acid batteries, they have not required a top up.

The alternator does get hot, and the Sterling will cut the current draw on the alternator when it reaches 100 deg C, which it does if pootling around town whilst kicking out 100 amps. On the open road the temp is kept down by the air flow through the engine bay, and the fan on the front of the alternator, and it is never an issue. The batteries only draw 100 amps for about 20 minutes, this bulk charges them, and then the current is reduced. The batteries are isolated from the alternator every 15 minutes and the voltage accurately measured and a computerised charging strategy formulated. When the batteries have reached full charge the voltage is reduced to 13.6 volts to prevent boiling.

I have flattened both batteries in Corsica when at a campsite for 4 days without hook up, running the compressor fridge and roof fans, etc. The batteries were fully charged after a 2.5 hrs drive.

With traditional split charge relays you would be looking at 14+ hrs to re-charge, but re charge they will, and if your electricity demand is not great then the split charge relay system is fine.

I have a large energy draw in my camper that a split charge relay would render useless for more than one nights camping that is not followed by a full days driving.

The standard bosch 90 amp alternator will kick out 70 amps at tick over with the Sterling switched on. If I turn it off, this is reduced to around 30 amps, and quickly falls away as the battery voltage is restored. The sterling avoids this under charging by working out what the battery actually needs to re charge it, rather than just relying on the system voltage, which is only one part of the story.

The Sterling system was developed for Yachts that rely on the boat engine to charge the batteries as fast as possible, and get the maximum amount of stored energy into the battery. This is only done by charging at a constant 14.8 volts, charging at 13.6 gives only 70% of the possible total charge.

Every split charge relay system that I have used, even on a brand new factory T4 suffered from poor charging when really put to the test, and this system makes the best use of your batteries and your alternator. I could happily get away with a smaller alternator.



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