Alternator Voltage Boosting is it advisable?

Hi
In my Troopy with a temperature compensated alternator that starts at 13.9v and after the motor is hot reduces to 13.6 volts.
Toyota engineers have selected these voltages to best suit the charging rate and life expectancy from batteries under high bonnet temperatures in vehicles such as mine.

The following is an extract from Solar Professional’s website – similar information is available from other battery professionals.
“Specifically, cold batteries require a higher charge voltage in order to push current into the battery plates and electrolyte, and warmer batteries require a lower charge voltage to eliminate potential damage to valve regulated lead acid (VRLA) cells and reduce unnecessary gassing if flooded cells are used.”

“Applying normal target voltages to a battery that is hotter than 25ºC may result in an overcharged battery. This condition could lead to the drying out of VRLA battery cells. With flooded cells, the result will be excessive outgassing, increased battery maintenance in the form of more frequent watering and reduced battery life due to thermal stress”

“Temperature Compensation Formulas
The most widely used temperature compensation formula is:
-0.005 V per ºC per 2 V cell”

End of Solar Professional quote

If you don’t like doing the calculations go to battery websites such as Power Stream and read directly from their tables.

My diesel has an under bonnet temperature of around 80 degrees C.
Once up to temperature I have measured my batteries electrolyte above 60 degrees C.

Examples using a nominal charge voltage of 14.5 v at 25 deg C

At 65 deg C is .005 x 40 deg difference x 6 cells = - 1.2 volt
Temperature compensated charge rate 13.3 volt

At 55 deg C is 005 x 30 deg difference x 6 cells = .9 volt
Temperature compensated charge rate 13.6 volt.

I believe Toyota have their voltages set about right for the temperatures under my bonnet.

For a second opinion of under bonnet temperatures go to the Century website and look at their Under Bonnet Temperature Logging of Falcon and Commodore vehicles in Melbourne and Sydney.
These ranged from 73 to 85 degrees C under the bonnet with electrolytes in the range 55 to 72 degrees

For those that install voltage increasing diodes they will obtain a faster charge but have a shorter life out of their batteries - I will stick with the original Toyota voltages.

I should have added, the output voltage of a low voltage alternator with a booster diode fitted is usual slightly lower than your standard old alternator, ie charges at around 14.2V to 14.4V @ 22C.

A DCDC charger, charges at approximately 14.4V @24C CTEK (AGM) and 14.5V Redarc (AGM)

They are all virtually the same.

Hi Leigh
I appreciate you have to promote your product.
My voltage is 13.9 at startup and 13.6 when hot – the mechanic says this is the recommended level for my motor. He advises against boosting it.
A lot what you say is generalisation without data or numbers to back it up.
My mechanic services a lot of these vehicles and he hasn’t experienced premature battery failure in them – in fact Toyota gets an excellent life out their OEM batteries.
I didn’t discuss the difference in under bonnet temperatures between similar sized diesel and petrol motors as it is not a thing people generally measure. Please quote the source of your figures.

Dennis,

If your under bonnet temperatures are normally that high then you have more to worry about than charge voltage, were they measured with the car being driving, what was the ambient temperature?

Your talking perfect world figures, ie batteries located in a battery room that are being floate charged 24/7, not in a car, if you go that path then you shouldn't even be charging your batteries once the temperature reaches 50C.

Alternators have been temperature compensated since they were first installed in cars, the temperature compensation curve is generally the same for all alternators and was developed as a trade of between battery life and reasonable charge times, it is not model specific, the same model will be used in various model cars of different manufactures, all will have different under bonnet temperatures, do you think the car manufacture actually specifies a particular temperature compensation curve for each model?

Booster diode was developed to restore the charge voltages of the current generation of low voltage to approximately that of a standard alternator, a petrol Prado has a standard alternator yet runs higher temperatures than the Diesel model why, because they didn't need to change it to meet the new emission standards. I again suggest you do some research on the subject.

The point here is we need to charge batteries in a reasonable time frame, if you install a DCDC charger under bonnet it will charge at approximately the same voltage as a standard alternator or boosted one at a given temperature, as the temperature under bonnet increase the voltage will reduce.

As I have repeated several times the current high compensations alternators were developed to allow the diesel engines to meet strict overseas emission requirements, some newer models more or less turn the alternator off for the same reason.

Bottom line is if you don't booster the alternator voltage then you need to install a DCDC charger to charge your auxiliary battery and it will increase the voltages to the same level anyway.

There are thousands of booster diodes in use and have been for around 7 years now, have you read of a flood of dieing batteries, I haven't, I sell these units world wide, to many auto electricians who think there the best thing since sliced bread and to many 4X4 shops etc.

I personally have had one in my Prado now for 7 years and haven't needed to add any water to any of my batteries.

I'm just wondering now why you actually posted, you indicate your happy with your charge rate but then ask about booster diodes, but when given information you requested you reject it, what was the actual purpose of your post?

Hi Leigh
You ask “If your under bonnet temperatures are normally that high then you have more to worry about than charge voltage, were they measured with the car being driving, what was the ambient temperature?”

This shows that you don’t know the extent or understand the under bonnet temperatures of vehicles.

My under bonnet temperatures didn’t vary a lot with the ambient I sampled them many times when driving, mainly on bitumen. They would have been hotter in the sand in low range 4WD. I measured in ambient temperatures around 30 degrees – I excluded those below 25 and above 35.

My temperatures tally closely with Century’s – theirs were sedans on bitumen – go to their website and check them out.
By the way I also measure water temperature and block temperature with a digital alarm monitoring system – all are up to specification.

You ask “but when given information you requested you reject it, what was the actual purpose of your post?”
The purpose of the post was to get differences of opinion and to get an idea of other’s experiences – it is achieving that.

Leigh,
Your diodes advertise a 0.5-0.6V boost. I was expecting a normal diode would give 0.7V, or is there something I've missed?

If you were to use a schottky diode, and gave a more reasonable 0.3V boost, then I might be a fan.

Cheers
Phil

Hi Phil,

The voltage drop depends on the device type and where it is operating in its forward current curve, ie the more current though the diode the higher the forward voltage drop.

Very little current flows in the sensing circuit so the diode will be operating at the low end of its forward voltage drop.

Actual drop depends on the vehicle model an alternator type.

I did do a low boost version at one time but they weren't very popular, 99.9% of users want around .5V, if you want less I can do a special but don't normally stock them.

Cheers
Leigh

PhilG,

Just a thought, you could try ABR, he might have a low boost version, and also Piranaha, I believe they are marketing their own version now.

Cheers
Leigh

Thanks Leigh,
I understand now!
Cheers
Phil

Hi Ross
I knew there would be lots of differing opinions on this.

Under a 2008 70 series V8 bonnet with two large batteries there is no room for insulation or a cooling system.

I am most particular what batteries I use under the bonnet - I use 2 Century Marine Pro 730 which work very well (low gassing and very low water consumption) as did the Toyota OEM battery. I won’t use a VRLA battery because you can’t service them.

That’s a good idea about the switchable diode – It won’t long before someone steals your idea and starts marketing them. I don’t think I will bother though, but thanks for the thought.

Dennis,
Do you mean there is no way you can add a radiant heat shield or silver reflector with some insulation so engine radiant heat is reduced?
I cannot see why it can't be done, but will be custom fitted. Also a cover which forms over the general battery area can be fed with a flex tube so cooler air displaces hot air trying to contact the batteries external surfaces.
That will surely reduce battery temperatures.
I have fitted a couple but not to V8 Cruisers.
Fed with ambient air, the batteries have to be better off than just sitting in a well of engine heated air and radiant heat.

If concerned about battery life, then why not?

The switchable diode I had on my 60 series and the alt voltage was a bit low, so two diodes were added with a switch which brought one or two into circuit. That way a selection could be made, particularly suitable for stopped running to recharge batteries outside the engine bay where a lead had some lessening effects.

Ross,

With the under bonnet temperatures his getting and the charge voltage he sees he should not have any charging issue to start with.

The booster diode is only for vehicles suffering from a low charging problem, as he obviously doesn't have a charging issue he doesn't need one.

Hi Tony
I think you are the most polite person I’ve met on this site.

You may be in a minority there Dennis, as you have said before, its sometimes hard to sort the chaff from the hay. I myself like to invoke discussion to, expirience we know is the best teacher, so if we can pass on knowledge and have a bit of fun at the same time, all is good. Dare I say, but some people do take themselves a little seriously at times.
Continue the good work in stirring the pot.
Cheers and stay safe.
Tony F8.

Please you 2 you are making me sick..! LOL

Razerback speaks the truth!! lol not really, you have to sort the wheat from the chaff

Not a grain of truth Bonz?

hahahaha well maybe a grain, but you have to take everything here as advice and make up your own mind, even from me....especially if its from me !

Now you have removed the voltage booster – it will interesting to see the difference in the life of your batteries.

As most of you have scan gauges, its is best to check it after a night with the car unlocked. I have a PJ Ranger with an alternator that charges at 14.2, but if I leave the car in the garage unlocked over night it can get down to 12.43v. If all your start batteries are dying think about locking the car to turn of the computers, just a thought.
Matt

As a matter of interest, have you split the batteries, ie only one for starting?

If you have an auxiliary fitted, how;s the aux doing?

Matt,
I wouldn't trust the scangauge voltage - mine reads 0.2-0.4V too low which is a lot.

Phil
Mine does to, that is why I crap myself when I sore the gauge and did further testing over a few nights. With the car locked it was 12.68 compared to the 12.43 unlocked at the battery. it would explain why I have lost preset radio stations a few time.

Boobook, if it helps I haven't fitted a booster diode to the 200 series and the original batteries are still going strong after six years.

Hi

Batteries can have short lives for a number of reasons and of course they don't last for ever even if treated with full respect. I am lead to believe 5 years is not unusual "on average" but suppose it varies considerably. I have gone through 3 main batteries in 10 years, and 1 auxillary (deep cycle) in 3....and until about 2 weeks ago didn't have a diode fitted.

So figure that by itself, stating that two batteries have died apparently prematurely (how old was the first one to start with?) when a diode was fitted doesn't provide enough evidence to come to any conclusion whatsoever. As Dennis points out - time may provide some answers but any observations are unlikely to be conclusive.

Cheers
Greg

Cheers
Greg

My scangauge...( and now an Ultragauge ) have read the same as my GME CB.....and the same as my Kyritsu digital multimeter..

If you do a lot of travelling.....and you want to use the alternator to charge camper batts....and you have a newer "smart" alternator....then the booster diode is a good thing..

But people who are happy with what they've got, shouldn't really post up and bag the diode...as it doesn't apply to them..

Yes Phil,
What you say makes a lot of sense
I took the isolator out and now have 2 x 100ah marine batteries close coupled to each other.
Fridge circuits have an independent VSR set to drop off at 11.5 volts.
The batteries have no problem cranking at that voltage.
I get a digital read out of voltage, water temperature and block temperature as I travel.

"shouldn't really post up and bag the diode...."
Huh?? Where did I bag the diode?

nobody said YOU did !!

Pop,
8 years! – don’t change a thing, nothing can improve with that.
You probally think I went overboard but I only started measuring under bonnet temperatures when I had a battery under the bonnet that was excessively gassing – it eventually boiled itself to death.

I think your 6 cylinder Troopy has its battery on opposite side to the exhaust.
With the V8 Troopy the exhaust is both sides and the rear battery runs pretty hot.
I once put a lead antimony, deep cycle, flooded battery in that spot.
It didn’t like it one bit and spat acid everywhere.

I now only consider putting a calcium/antimony, flooded, marine or starter battery in that spot.

Gee Pop, you sure are abusing those batteries.
8 years is just not good enough. It is obvious you will have to add the water more often!
Cheers
Ross M

Yeah, I know Ross, I'm just a lazy bugger (;_((

Cheers
Pop

Dennis,,

All kidding aside, posts like yours scare me. As much as I am resisting the thought of retiring my old banger, which you are right about re battery and exhaust orientation, I know that very shortly I am going to have to replace with a new vehicle.
The new 70 series dual cab is under consideration but not sure if something like a D-Max might be all I need. Battery v exhaust positions could be one consideration out of many.

Cheers
Pop

Hi Pop,
You won’t have a problem with batteries – the original Toyota batteries are very good.

In the 2008 70 series you could fit 2 batteries under the bonnet – the newer models will only take one as they now have an ABS computer where the no 2 battery used to go.

The only problem I had battery wise under the bonnet was with a lead antimony deep cycle in a hot location.
This battery was recommended by the maker’s rep as being a good deep cycle battery for my application.
Lead antimony construction is good for deep cycle batteries, but they gas readily in hot locations or when subjected to overvoltage – something the rep didn’t appreciate.

No interference. The DC-DC charger will work just as well with, or without a booster diode.

As above, no problem running both, would it be worthwhile though?

Depends, if your alternators running on the low side, fitting a DCDC charger, especially the higher amperage units can have an adverse affect on the cranking battery as the load can drop the alternators voltage even more and reduce the already low charge voltage to the cranking battery. It would also allow the use of the non LV versions of the DCDC chargers.

An added advantage is you will also have brighter headlights as the globes will be running closer to their design voltage.

Cheers
Leigh