Alternator relaxer

[DieselJan]

Hi Everyone
I have been reading around on ecomodder for about 2 years and learned a lot and implemented quite a few things that I learned, Thanks for it.

I tried to do an alternator delete but just couldn't get it working properly, as my alternator has an internal regulator.

So I had an idea but tried a few different things before eventually getting to design and build it. I can't really tell the mpg(km/l here) difference it makes, but my vehicle surely idles much easier when the alternator relaxer is working.

I have been testing the circuit for 6 months and it works without problems.

[DieselJan]

Ok, so I have to split it up a bit so I can eventually ad a circuit diagram.

The circuit is a sort of automated system where you don't have to charge the battery off electricity if you choose not to, as it uses a sort of regenerative breaking/charging, which you can configure as you like.

My regenerative breaking works only when I press the break pedal, or when the break lights comes on. It can take multiple inputs so you can configure it to charge battery when you feel the alternator must help slow down the engine. With switch at petrol pedal, toggle switch inside car, or whatever you like.

It can also easily be changed to work with deep cycle batteries, or normal lead-acid like mine. Set the minimum battery discharge voltage to your requirements. So if you have a deep cycle battery, set the minimum discharge voltage to the minimum that will will not affect the life of your battery. Or have a low minimum voltage and recharge at night.

[DieselJan]

You can also configure it to charge the battery at different rates during breaking depending on your battery. So lets say your alternator used to charge at maximum 14V, you can make it charge 14,3V ; 14,4V; 14,5V ; 14,6V ; 14,7V ; etc. during regenerative breaking.

Off course you cannot make it permanently charge at too high voltage, or it will cause a lot of gassing and eventually cook your battery to death.

This was the other reason why I made this mod, as my alternator was configured to charge at 14,7V. This caused a lot of gassing and wasted power. I had to top off my battery quite regularly to keep the cells wet, and stop sulfation happening.

I put in a new regulator but it only brought down the voltage to 14.42V and I could still see the battery gassing and causing wet spots around the caps.

[DieselJan]

Ok, so here it is. Here is a quick description of how it operates.

The Lm358 op-amp and circuit around it is an oscillator. The oscillator is used to generate a voltage that is higher than the battery voltage, to "fool" the alternator. This higher voltage is fed to the Sense input of the alternator. The sense voltage is clamped to be 1,02V higher than the battery voltage by the 2 diodes marked in pink on the circuit.

This means that the alternator, in my case, will charge the battery until the sense input is at 14,42V. This 14,42V is what the factory internal regulator voltage wants to get. But because of the diodes in pink on the circuit, the battery voltage will actually be 13,4V when the sense input is at 14,42V. This difference is caused by the 1,02V drop over the pink diodes.

Now if I press my break pedal and the break lights comes on, the oscillator(charge pump) circuit stops working. This is done through any of many diodes in green at bottom of circuit. Everything is basically not working except for the diode at the top of circuit(HER508). This causes the alternator sense input to be 0,3V lower than the battery voltage.

Now suddenly the alternator sees the battery voltage is low and starts charging the battery at a fast pace. In my case it will charge the battery until the battery voltage is at about 14,72V. This draws more power from the engine and is used as a sort of regenerative breaking.

I have only 1 diode in the green highlighted area but you can add as many as you want, from a switch inside vehicle, maybe at night when your lights is on or switch when foot is off petrol pedal and vehicle in gear. As long as it gets the 12V in through the green diode the circuit will switch off and alternator will charge battery at higher voltage.

The circuit is only switched on when the car ignition is on. So it doesn't draw any current when car is switched off.

[DieselJan]

The diode right at the top is indicated as 0,3V(marked HER508). The HER508 actually has a voltage drop closer to 0,4V. Germanium diodes normally have a voltage drop of 0,3V. Other diodes like 1N4007 has about 0,5V to 0,6V drop.

So depending on what high charging voltage you want, you can change that diode to a different one or put 2 or more in series. Lets say your alternator stock charges at 14V, and you want it to fast charge at 15V, you simply add 2 of 1N4007 diodes in series in the place of the HER508. Or add the 2 diodes and put a bypass switch inside cabin to bypass one so that you can decide what you want the voltage to be. 14,5V or 15V.

Remember that there has to be at least 1 diode in the position of the HER508 or it will work as stock, and the circuit will have no effect except using some power.

You have to measure your charging voltages before putting in the circuit so you know how to set it up. Mine was 14,42V stock. I also measured the current drawn by the sense input of the alternator. It was 1.5mA on my alternator, and designed the circuit around that. The circuit total current consumption is about 5mA when running.

If your alternator sense input draws more current, simply replace the 470 ohm resistor value with something like 390, 330, 270 or lower resistance. The lower the resistance the more current the total circuit will draw. You will know that resistance is too big if the battery voltage doesn't go low enough below the regulator voltage of your alternator.

Not all alternators has a sense input so you will have to do some research according to your car's alternator to see if this circuit can work for you.

[DieselJan]

The circuit is configured so that when I break, it will switch off and charge the battery at higher voltage for about a second and a half after releasing the breaks. This is so that if I do pulsed breaking to stop wheels locking for example, the breaking effect of the alternator is constant.

This timing circuit is formed by the 18K ohm resistor and 10uF capacitor at bottom. To make time longer put in a bigger capacitor or resistor, to make it shorter make the resistor or cap smaller. Preferably only change the capacitor.

I set my voltage in normal, non breaking, mode to be 13,4V. This is like a float voltage for lead acid batteries. So the battery will charge at a very, very slow rate, but stay around 90% to 100% full. The regenerative break charging will keep the battery close to full, or sometimes overcharge to help for sulfation, depending on how much it is used.

If you turn up your radio or use lights at night, the voltage won't drop below the 13,4V in my setup. So I never need to charge my battery from electricity to get it full. Of course if you have solar panels on the roof, you can make this voltage lower.

Temperature affects battery charge voltages, so if you live in very cold climate, you can make the high charge voltage higher as well as the float charge voltage. Or leave the float charge where it is.

Maybe all this information is a bit too much, but I wanted to explain it well for people who want to use it a bit differently. So build it as it is and change it from there if it doesn't work correctly for you.

I would like it if someone with a scangauge can build this and give some feedback of the mpg effect. My diesel pickup works on a fill-up and work out the consumption basis. There is no cheap way of seeing the immediate consumption.

Remember that this circuit might or might not confuse vehicles with too much computing power. Luckily my vehicle's most complex circuits is the alarm circuit. If it does confuse your vehicle, try changing the 10uF capacitor next to 15V zener diode to something bigger like 47uF. This will make the transition between the low and the high charging voltage slower.

Before I forget, all capacitors should be of value 25V and higher. If you want your high charging voltage to be more than 15V, you will need to change the 15V Zener diode to something a bit higher than what voltage you want. The Zener diode is there so that the circuit doesn't send a too high voltage into the alternator and damage it. Normally a battery shouldn't be charged much higher than 15V anyway.

Enjoy
Jan

[gumby79]

Nice write up

How would you do this as a window ?? Charge on at 10v and off at say 14.7 to cycle a deep cycle

[teoman]

Can we have a picture of the actual circuit?

[freebeard]

The picture went up at 11:08AM in Permalink #4 above.

I'm going to have to think about this.

[ThermionicScott]

That's a neat trick. I think most of us, even EcoModders, just think of an alternator as something that robs HP when needed, but haven't really explored fine-tuning how much it's used. And it's certainly good to do something that avoids frying batteries!