Over-charging the battery to ease alternator load

[topcat]

I noticed after I had my cheap battery charger charging the car battery that the starter motor turned over faster. I guessed that the battery charger had put more "juice" into the battery than it would normally get from the alternator.

If I can slightly over-charge the battery before each trip, then the alternator would not need to put so much in during driving, thus easing the load on the engine and ultimately using less fuel.

This led me to thinking whether I could hook up a semi-permanent system to allow this to happen overnight. I already have a block-heater IEC mains lead going in, so maybe I could use this to power a small lightweight charger kept in the engine bay, permanently connected to the battery. Then when my block heater is powered, my battery is getting topped up too.

So I bought a CTEK charger designed for permanent connection. But this only charges to 14.4V, (the same as the alternator). I do not see the same effect on the starter motor turning faster after I have used this CTEK charger. CTEK do another model which charges to 15.0V, but I've blown the budget now...

So I found an old PSU from a Toshiba laptop, which gives out 15.0V (up to 4Amps), weighs less than 1Kg, and has very low ripple (measured < 10 mV), and very low back current drain (<10 mA). I've done some tests on an old battery (off the car). Now I'm considering using this permanently connected under the hood. i.e. clamp it near the battery.

Questions:-
- Is it safe? I'm pretty happy that the chargers are about as safe as you can get, millions of Toshiba laptops around. Never heard the chargers catch fire.
- Will 15.0V charging kill the lead acid battery eventually?
- Will the alternator adjust its load to take account of the fact the battery is already charged? (Car is 2005 Toyota Celica 1ZZ-FE engine, surprisingly quite efficient!)

[Daox]

This effect will only last a few seconds at most. The battery voltage will very very quickly drop down to whatever the alternator is putting out. If you're looking for gains in the alternator area the best way to go is to put a deep cycle battery in and delete the alternator in some way.

[pete c]

Overcharging a battery will boil it dry if done for extended periods. Been there, done that.

As to whether this charger will, I can't say. Personally, I don't think the miniscule potential savings are worth the risk.

My suggestion would be to run an extension from the charger you already have. Zip tie it to the extension cord you use for the block heater. run a cable from the battery to the block heater plug in. This way, you use the already proven charger and you are not dragging a questionable charger along that would have to live in a hostile environment it wasn't designed for.

[topcat]

Originally Posted by Daox

This effect will only last a few seconds at most. The battery voltage will very very quickly drop down to whatever the alternator is putting out. If you're looking for gains in the alternator area the best way to go is to put a deep cycle battery in and delete the alternator in some way.

I think it would last longer than you suggest. The volts will match the alternator, but the fully charged battery will not be able to take much current out of the alternator. Therefore not much power is taken.

If I charge it with 2Amp x 12.6V for 2 hours that is 0.05 kWh of energy put in.
There is ~9kWh in 1 litre of petrol, a 33% efficient engine means there is 3kWh of usable motive energy in 1 litre.

So it could potentially save ~1-2% of a litre. Not a lot, but worth having. Minus of course the cost of the electricity from the socket. But electricity is £0.10 per kWh instead of the £0.14 /kWh petrol which is £0.44 / kWh assuming 33% efficiency. (Using UK prices).

[Ryland]

You don't want to boil your battery unless you have a charger that is designed to do an equalizing charge and most car battery chargers don't do that, they just do a float charge, much safer for the battery.
The only advantage to the higher voltage is that the starter spins a little faster, I don't think this will help your gas mileage and the battery is not going to have that much "extra" energy in it from being over charged, the advantage that you will get from charging the battery before you drive is that your battery might last you 20 years (if you don't boil it!) and that your alternator isn't going to have to work as hard to make up for a part charged battery because it was sitting over night.

[SiVX]

Originally Posted by Daox

This effect will only last a few seconds at most. The battery voltage will very very quickly drop down to whatever the alternator is putting out. If you're looking for gains in the alternator area the best way to go is to put a deep cycle battery in and delete the alternator in some way.

I would LOVE to do this. I've already converted headlights to 35w ddm tuning hid's. Dome light to LED. Same with reverse lights and license plate lights. I'd love to go full led with the other rear lights. Also, I want to track down the wirimg diagram and set the front center marker lights to only come on during the marker light setting and not with headlights. Also in a day or two I'm swapping my friend his clock block for my real clock. Here's the coolest part. I'm gonna mount to bolts sticking out of the clock block and use them as hangers for my mpguino box! Its gonna look so sweet and i won't have to pull eyes far off road at all to monitornlean burn or fe.

Interesting idea here tho. When you use an LED buld for dome light, after turning off car it will stay lit very dimly because the dome is somehow connected to the radios memory power. This tiny bit of power is enough to keep led slightly lit. Not a big deal, but I decided to buy an additional dome light and mount it up front as a map light. It will be very easy to wire in series with the existing dome light. Result equals map light, more lighting options and the bulbs won't stay lit because the second led from up front will act as a small resistor

[brucepick]

Reducing the amount of work the alternator has to do is definitely a good thing. My alternator has been mostly "out to lunch" since Feb. 28, with very nice results, thank you. Please see my project thread: http://ecomodder.com/forum/showthrea...tml#post286282. You can also see my gas log, see my info at left or my signature's graphic.

Charging at more than "correct" voltage definitely isn't good for a battery. Boiling the acid bath is the result, which means the acid will vent so you will lose some of it every time it boils.

Short of doing a full alternator delete or "EPES" as I did, I suppose you could substitute a deep cycle battery for your standard "starter" battery. Charge it on a correct charger before driving and your alternator will have somewhat less work to do. But the bigger gains come when you can drive with the alternator's output wire disconnected or switched off. Or better yet, remove the alternator belt. I didn't take that last step because I want to be able to quickly restore the alternator to use.

[radioranger]

easier than all of this is a larger pulley for your alternator to slow it down, makes a detectable difference in the accelleration in the Ranger.then maybe put a solar panel in the window to pick up the 1 amp to keep the battery up , not cost effective though a pulley and maybe a new drive belt maybe 35 $ and adds to pickup and milage , win win

[radioranger]

Most of the MPG lost in a alternator is speeding up the heavy armature all the time, thats where the bigger pulley gains , and it will help

[radioranger]

of course you could always manually switch on the alternator when coasting or if the battery gets low on voltage.