# Anyone know the max charging current from a typical alternator?



## Firefox (Oct 23, 2009)

Rather than put the aux battery charge on a split charge relay switch I was going to put it on a manual switch but with a trip. I'm happy with this method as it is what I've used before and it gives you more flexibility. My aux batteries are of the dual purpose type so can be used for starting.

Anyway, one can buy quite cheaply high current switches designed to replace fuses in a domestic 240v box with the added function that they trip if the current was too high. I think these would be suitable for the charging circuit on/off and also the aux electrics on/off. Can get them in 35 Amps, 20 Amps etc.

What would be the max charging current from an alternator for a 2.5L TD engine (Vaux Movano/Renault Master) on a flattish leisure battery? I was thinking the 35A would be enough. 

And maybe 20A for aux electrics on/off?


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## AndyC (Oct 23, 2009)

The alternator will be capable of producing more than 35A, I would think you could well get more than 35A in the charging circuit for a short period, particularly if you are using heavy duty cables and have several batteries.

Without knowing the sort of installation you are planning, I'd be inclined to use 10mm csa cable and a 50A breaker as a minimum.

You'll need to check with your supplier that the circuit breakers are suitable for DC.

AndyC


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## Readytoroll (Oct 23, 2009)

Be very carefull doing this. 

Just for charging an aux battery, you do no need to much beef in the cable and 10mm would be fine. Where you can get problems is if your starter battery went flat and you forget to isolate the aux battery, your starter/engine will draw tons of amps through the cable and turn it into a fuse causing all sorts of dramas.

I would use 20mm with one of these installed...  200amp 12 Volt CAR HIGH CURRENT Circuit Breaker 200 AMP on eBay (end time 18-Oct-09 21:17:32 BST)


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## Firefox (Oct 23, 2009)

Good points. I'll check out the switch though I think AC switches are OK for DC so long as the voltage is small like 12V as you don't get much arcing with only 12V even if the contacts are close. 

I'm intending to use a really heavy cable like jump lead standard for the charging circuit to cut down on voltage drop as the batteries are in the back so it's a 4m run of cable.


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## Readytoroll (Oct 23, 2009)

Firefox said:


> AC switches are OK for DC so long as the voltage is small like 12V
> 
> 
> 
> ...


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## lebesset (Oct 23, 2009)

hi , I did this for years using always 6mm cable 
but make sure that as well as the switch you put a 35 amp maximum automotive fuse in the line 
that way , if you have a senior moment [ you don't need to be a senior to have one of those  ] and forget to switch off , the fuse blows if the current drain is too high !


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## maingate (Oct 23, 2009)

What`s the scrap value of a burnt out van these days?


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## AndyC (Oct 23, 2009)

Readytoroll said:


> Be very carefull doing this.
> 
> Just for charging an aux battery, you do no need to much beef in the cable and 10mm would be fine. Where you can get problems is if your starter battery went flat and you forget to isolate the aux battery, your starter/engine will draw tons of amps through the cable and turn it into a fuse causing all sorts of dramas.



An appropriately rated breaker would trip and prevent any dramas.



> I would use 20mm with one of these installed...  200amp 12 Volt CAR HIGH CURRENT Circuit Breaker 200 AMP on eBay (end time 18-Oct-09 21:17:32 BST)


Then you'd need to use cable capable of carrying over 200A.

AndyC


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## AndyC (Oct 23, 2009)

Firefox said:


> Good points. I'll check out the switch though I think AC switches are OK for DC so long as the voltage is small like 12V as you don't get much arcing with only 12V even if the contacts are close.
> 
> I'm intending to use a really heavy cable like jump lead standard for the charging circuit to cut down on voltage drop as the batteries are in the back so it's a 4m run of cable.



Best stuff to use is the cable sold for use with arc welders, check out your local welding supplies shop. If it's a 4m run of cable, and you've got 2 or 3 batteries, I would suggest at least 16mm csa cable to keep the voltage drop low (25mm would be better). If you get the welding supplies place to cut you the right lengths of cable they'll probably crimp the ring terminals on for you.

AndyC


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## AndyC (Oct 23, 2009)

Firefox said:


> Good points. I'll check out the switch though I think AC switches are OK for DC so long as the voltage is small like 12V as you don't get much arcing with only 12V even if the contacts are close.



In fact you can get a more sustained arc with DC than with AC. It's because with DC the current is constant and tends to maintain the arc, whereas with AC the current cycles up and down through zero so tends to break the arc.

AndyC


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## wilse (Oct 23, 2009)

Not sure if this helps?? but in my truck Adria Vision 707SG, when the engine is running I can check the charge going to the batteries on the digital control panel [Schaudt]... the charging is around 18 Amps.
This is probably choked by the charger, as I would assume that the output is higher.

w


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## Readytoroll (Oct 23, 2009)

AndyC said:


> Then you'd need to use cable capable of carrying over 200A.
> 
> AndyC


Agreed, but if you use 20mm cable like the rest of the system should be (or there abouts), it will be more than adequate and the breaker or fuse in theory would not be required (though it should be fused imo) but would help in overloading situations and act as an effective isolator switch.


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## maingate (Oct 23, 2009)

I cannot watch this thread anymore without chipping in on safety grounds.

Most chargers deliver less than 20 amps and there is a reason for that. To bang a load of amps into the battery in the shortest time possible will wreck the battery (or the alternator) and burn out the wiring if the self built circuit is not balanced.

Why not ask somebody with a coachbuilt or bought van conversion for a copy of their wiring diagram as a template. Failing that, have a chat with a qualified auto electrician and he will tell you why you are an accident waiting to happen.

My son was a qualified auto electrician and is now a fire fighter. He says he is bound to come across you if you wire in your van as you intend to.

DIYers can do most things on a van but designing a high rate charging system is not one of them.

Sorry to be so blunt but I am genuinely worried by the way this thread is going.


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## runnach (Oct 23, 2009)

Well tbh I have more chance of understanding Sanskrit than some of the threads here.

To re iterate the Op's original question if I read it correctly what typiccally in terms of amps does the alternator pump into the leisure battery.

The reason I ask is I have a new 85 amp battery and evenings spent in the dark chatting with the occasional spider seem to make no difference two days flat !!!

My problem I will ask elswhere, but I would be interested in an answer to the op's original question. ( if only to learn a bit of Physics I was missing it seems that day at school)

Channa


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## tan-all-over (Oct 23, 2009)

*Anyone know the max*

Ok, I admit it. When I saw the title "any one know the max" I thought we where talking about "Max and paddy" road to no where. from the tv show. Ok I get my coat.


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## maingate (Oct 23, 2009)

The alternator does not pump power into the battery.

The battery charger takes care of that by regulating how many amps of 12v is fed to the battery. They are designed to give a good charging rate that will not damage the battery.

An alternator can give out enough power to run everything you need plus charge the vehicle battery as well.

If you have a flat battery in 2 days then double up with another 85ah one. Or you could investigate why you are using so much power.

Nobody ever said life would be easy. That is why we a) Have a sense of humour and b) Get blind drunk on occasion.


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## rickboy (Oct 23, 2009)

*Kis*

 Keep It Simple 

Another solution I have used  if you already have the kit,but not a recommendation-you decide!! (230 volts and all)

Short 12volt  fused heavy lead to inverter.Long as you like 230volt cable to battery charger/s.

Now that should put the cat among the pigeons.


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## runnach (Oct 23, 2009)

maingate said:


> Nobody ever said life would be easy. That is why we a) Have a sense of humour and b) Get blind drunk on occasion.



Hopefully guilty of both charges.

In my simple mind, say for example the battery via the alternator is getting 5 amps an hour then it would take 17 hours of driving to fully charge ?(85 amp battery )

this may possibly be reduced i.e the 5 amp figure if lights are on the vehicle I am running the fridge? in other words the alternator is having other tasks to deal with.

hence my question re the amount of amps pumped into the leisure battery.

Johnny thick kid is trying to make sense of all this ,is my theory of physics seriously flawed? and what realistically can a typical charger pump into the leisure battery per hour.

In my case the charger may well not be up to speed from the sounds of it ...

Channa


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## AndyC (Oct 23, 2009)

maingate said:


> I cannot watch this thread anymore without chipping in on safety grounds.
> 
> Most chargers deliver less than 20 amps and there is a reason for that. To bang a load of amps into the battery in the shortest time possible will wreck the battery (or the alternator) and burn out the wiring if the self built circuit is not balanced.


I thought we were talking about alternators, not battery chargers. A 20A battery charger may well be adequate for say 2 90Ah batteries but not if you have more that that. Alternators are self regulating, the amount of charging current will reduce as the battery is charged. A standard alternator is most unlikely to damage batteries, adequately sized wiring, or itself.



> Why not ask somebody with a coachbuilt or bought van conversion for a copy of their wiring diagram as a template.


Most commercially built motorhomes have under specified charging systems, to keep the price down.


> Failing that, have a chat with a qualified auto electrician and he will tell you why you are an accident waiting to happen.


Why?

I would advise talking with a qualified marine electrician, he will be much more familiar with optimum battery charging systems than an auto electrician would be.


> DIYers can do most things on a van but designing a high rate charging system is not one of them.


True - good to have a discussion about it though.

AndyC


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## bigtrev8xl (Oct 24, 2009)

I would recommend reading through this http://www.tb-training.co.uk/cover.html

Big Trev


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## Firefox (Oct 24, 2009)

Just to clarify; I'm not actually trying to fit a high rate charging system.  

My original question is what the charging current on a *standard* 2.5 litre diesel alternator would likely be when charging one or two (say) half discharged leisure batteries. This is to make sure if I fit a trip switch it is high enough rated.

My charging system is likely to be super safe because (a) It will have a very thick cable and (b) It will (likely) have trip in the circuit.

Fitting a bigger cable doesn't make it into a high rate charging set up. For that you need upgraded alternators and a charging management system


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## AndyC (Oct 24, 2009)

bigtrev8xl said:


> I would recommend reading through this http://www.tb-training.co.uk/cover.html


A lot of relevant stuff there - written by a marine electrician 

AndyC


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## maingate (Oct 24, 2009)

The only problem is likely to be how a marine electrician runs the earthing cables. Slightly different method to a vehicle.


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## bigtrev8xl (Oct 24, 2009)

maingate said:


> The only problem is likely to be how a marine electrician runs the earthing cables. Slightly different method to a vehicle.



I don't know if you have read through it or not, but it talks about the return (earth)
 through the metal hull or in our case bodywork, and using a cable for the return (earth)

Cheers Big Trev.


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## maingate (Oct 24, 2009)

Very useful if you are new to electrical systems.

I did most of that in the first year of my apprenticeship but I can appreciate it that it is double dutch to many people.

I did`nt realise I knew as much about boats.


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## Firefox (Oct 24, 2009)

That is actually a very good source. Most of the marine domestic stuff is relevant to a motorhome, even more so because it has to cope with harsher salt water conditions, and is thus over specified for a vehicle. They also have to deal with generally longer cable runs with attendant voltage drops.

In fact that's how I'm doing my wiring, as he describes on the domestic side, with cabled earth returns rather than relying on some local return through the bodywork, which isn't always convenient and not always reliable or maintainable either.


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## maingate (Oct 24, 2009)

Are you going to smash a bottle of Champagne on the bonnet when its finished? 

You could park it at the top of a hill to do it and then let the handbrake off.


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## Firefox (Oct 30, 2009)

I was thinking of welding up the floor pan and just giving it a gentle shove out into a lake a la Top Gear....

anyway you've got the 747, why don't you push it off a cliff to test out the wing mirrors


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## maingate (Oct 30, 2009)

Bit too hevy for me Firebox, I will get the wife to do it


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