How much diesel does an alternator use?
Discussion
I havent logged on to my solar controller on my camper for a while, but just giving the whole van a spruce up before putting it up for sale.
I logged on to the solar controller and since january 2020 my panel has put 4124Ah into my batteries, that is electricity the alternator hasnt had to generate from burning diesel.
Just out of idle curiosity does anyone know how to roughly work out what my £135 solar install has saved me in diesel. Its a 2004 1.9 dci renault engine with a 140a alternator.
I am guessing you would need to know the rough thermal efficiency of the engine, the rough conversion efficiency of an alternator and convert the electricity to joules work it backwards through those 2 efficiencies then work out how many joules of diesel it would take then convert that to litres?
Just curious. I am wondering if it was a cost effective install.
I have certainly never had a flat battery even when the thing has broken down many many times and needed tons of cranking.
I logged on to the solar controller and since january 2020 my panel has put 4124Ah into my batteries, that is electricity the alternator hasnt had to generate from burning diesel.
Just out of idle curiosity does anyone know how to roughly work out what my £135 solar install has saved me in diesel. Its a 2004 1.9 dci renault engine with a 140a alternator.
I am guessing you would need to know the rough thermal efficiency of the engine, the rough conversion efficiency of an alternator and convert the electricity to joules work it backwards through those 2 efficiencies then work out how many joules of diesel it would take then convert that to litres?
Just curious. I am wondering if it was a cost effective install.
I have certainly never had a flat battery even when the thing has broken down many many times and needed tons of cranking.
Would you have been running the engine specifically to charge the battery, or charging it as a by product during normal driving?
Engines are typically of the order of 25% efficiency although it can vary a lot.
A typical alternator is around 50% - 60% efficient although it can vary a lot.
But the load of an alternator represents just a tiny fraction of the efficiency of the vehicle as a whole, so the answer is probably: not enough to matter.
More important is whether it saved you the hassle of a flat battery.
Engines are typically of the order of 25% efficiency although it can vary a lot.
A typical alternator is around 50% - 60% efficient although it can vary a lot.
But the load of an alternator represents just a tiny fraction of the efficiency of the vehicle as a whole, so the answer is probably: not enough to matter.
More important is whether it saved you the hassle of a flat battery.
I run the engine to cook or have a shower as its all electric off a 6kw inverter, no gas.
The alternator has a decent regulator so puts less load on the engine when the electrical load is left. You can see the idle dip when you start the shower.
The mppt only supplies current when the battery needs topped up, so those 4000 amps must have done some work for me that the engine would have otherwise had to supply.
I seen on a hypermiler forum a set of maths to try and according to their sums i have saved around 60 litres of diesel over the years. Not enough to pay for the equipment but nice to know, it has done its primary job of keeping the batteries topped up when its unused, and supplying small loads like usb chargers when camping i suppose and firing up the diesel eberspacher. There is only 1 large panel on the roof but space for 3, but for all i use the thing it wasnt worth the extra strain on the mazda bongo electric pop top motors.
The alternator has a decent regulator so puts less load on the engine when the electrical load is left. You can see the idle dip when you start the shower.
The mppt only supplies current when the battery needs topped up, so those 4000 amps must have done some work for me that the engine would have otherwise had to supply.
I seen on a hypermiler forum a set of maths to try and according to their sums i have saved around 60 litres of diesel over the years. Not enough to pay for the equipment but nice to know, it has done its primary job of keeping the batteries topped up when its unused, and supplying small loads like usb chargers when camping i suppose and firing up the diesel eberspacher. There is only 1 large panel on the roof but space for 3, but for all i use the thing it wasnt worth the extra strain on the mazda bongo electric pop top motors.
OldGermanHeaps said:
I run the engine to cook or have a shower as its all electric
That sounds extremely inefficient, but if the cost doesn't bother you then that's no problem.If you wanted to save money, a diesel water heater and stove would be massively more economical that running the engine to generate electricity to turn to heat. A diesel heater would be close to 100% efficiency whereas your engine plus alternator would be lucky to break 10%.
Since i built the thing in 2018 or 2019 i cant remember i have cooked about 20 meals on the cooker and used the shower about 25 times for a few minutes each time. A lot of the time we cook on a bbq or campfire, have a takeaway, and a lot of the time we are on sites with a shower so it woulnt be worth the couple of grand and loss of cupboard space for a diesel heater, and a gas hob has disadvantages over an induction hob. Also for the first meal or 2 and shower or 2 we dont need to run the engine, its really just a precaution as i dont want to overdischarge, there are 335ah of batteries so i have probably been overcautious.
Its an instant hot water tap and shower.
Its an instant hot water tap and shower.
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