Thread: battery charger

Hi fella's, I have this brushless 24v alternator and i would like to get another volt out of it, it puts out 28.6v and i would like to fit it with a circuit that i could switch to every now and then to get 29.5v.
In the past I have achieved this with alternators that have slip rings by switching to a circuit that used 2 diodes in series to the regulator battery voltage sense terminal, this gives a lower voltage to trick the regulator into pumping more juice into the rotor winding and uping the output voltage.
This brushless alternator self energizes at about 1500 rpm and nothing I do with the diodes on the battery sense or the switch terminals on the regulator makes any difference, it doesn't even seem to matter whether any power is connected or not, except at low RPM power to the reg does excite the alternator.

Has anyone here got any clues as to being able achieve this??????

The load on the alternator adjusts the engine RPM to suit the load, there is still some work to do but it is working as it should, here are some pics of the alternator and where i am up to. This gen is actually Mk2, the first alternator I used had stuffed diodes so i had to modify things a bit to accommodate a slightly larger alternator....

Hi John,

The 24 volt regulator is potted and a fixed voltage and I doubt that you could modify it to output a higher voltage since it uses an internal reference !

However the input voltage to the regulator might be altered by changing the number of turns on the exciter coil. Try adding say 20 turns and see if that increases the alternator output. Either way it will still produce 24 volts. I suspect that the 28 volts that you are measuring could just be due to output ripple, you really need a scope to check that.

HTH.

Couple of ways you could do it without messing around with the windings

One would be to add a variable boost/buck module on to the output, however, current handling will become problematic there as they are only available relatively inexpensively in low(ish) current variants. They do exist for high current applications but the cost is an order of magnitude higher.

You could also remove the internal regulator module and replace it with an external one that is adjustable. A quick look at the results for searching ‘24Volt Adjustable alternator regulator’ says you have options readily available.

Simplest way is to put a diode in series with the voltage sense terminal on alternator. The terminal should be marked "S" and is a separate connection to the battery. I made a 12v charger from a 2.5hp 4 stroke driving a 120A alternator. By putting the diode in place with a switch in parallel to bypass it the charge voltage is increased by about 0.7V , 2 diodes will double this increase.

Originally Posted by BaronJ

Hi John,
However the input voltage to the regulator might be altered by changing the number of turns on the exciter coil. Try adding say 20 turns and see if that increases the alternator output. Either way it will still produce 24 volts.

Hi John, I think you might be referring to older style regulators with coils and points? Or have I completely missed what you are trying to explain to me?

Originally Posted by BaronJ

I suspect that the 28 volts that you are measuring could just be due to output ripple, you really need a scope to check that.

John lead acid batteries should measure 2.2 volts per cell when charged, to charge them you need 2.3 to 2.4 volts per cell.
I am getting about 28.6 - 28.8 volts charge rate total for 12 batteries, 28.6 / 12 = 2.38 v/cell.

A bit of squirt every now and then up to 29.5 or maybe even 30 volts helps to equalize the batteries.

Originally Posted by racingtadpole

You could also remove the internal regulator module and replace it with an external one that is adjustable. A quick look at the results for searching ‘24Volt Adjustable alternator regulator’ says you have options readily available.

G/day racingtaddy, I think that I will remove it and have a bo peek to see if I can disconnect the reg from the + output, it must be connected to that, I dont think it needs to be connected......then try my diodes?

Originally Posted by Sparksy

I made a 12v charger from a 2.5hp 4 stroke driving a 120A alternator.

G/day Sparksy, I reckon you have bigger horse's over in the west than we have in Vic.

Is this a permanent magnet alternator or does it still have slip rings and brushes (as in the first photo)?
PM alternators put out a lot higher voltage if allowed to by the regulator rectifier which is normally external. In which case it would be putting power out at all revs though. I don't quite get the construction of yours....

Originally Posted by shedhappens

G/day Sparksy, I reckon you have bigger horse's over in the west than we have in Vic.

No just normal size. Meant 65A alternator. Was thinking of the one I built my mate for welding of his 4wD.
2.5hp motor from edger, 65 amp alternator and a diode in sense connection to drop the sensed voltage from battery so regulator sees 0.7v lower. Switch on box selects charge voltage.

Charges batteries at about 45-50A depending on state of batteries but on dc load test easily got 70A.

Originally Posted by jhovel

Is this a permanent magnet alternator or does it still have slip rings and brushes (as in the first photo)?
PM alternators put out a lot higher voltage if allowed to by the regulator rectifier which is normally external. In which case it would be putting power out at all revs though.

Hi Joe, no not a p/m alternator. In pic No2 I am holding the rotor coil in my hand, it is secured to the rear alternator hsg by 3 screws and does not rotate, it resides inside the rotor and the rotor rotates around the coil, as far as i can see this alternator operates and/or functions the same as an alternator with slip rings, except the rotor windings are stationary.

Originally Posted by jhovel

I don't quite get the construction of yours....

If you have ever lived off grid you would understand the frustration of continually pouring fuel into a generator that is spinning over at 3000 rpm and often only pushing out a few watts, lots of fuel ($) and noise for little return.
With this design the alternator is mounted in between bearings that allow the alt to rotate and pull against the spring, the more power required the harder it pulls against the spring, as the lever that the spring is attached to moves it also pulls the throttle in unison so that more load = more revs, less load = less revs.
The last one i built i used a 24v 100a alt direct coupled to a 9hp honda, it was very efficient and run on LPG, fogged in in winter i would get about 5 weeks out of a house bottle, 50 bucks back then.
This one will run off the mains house gas.

Originally Posted by Sparksy

No just normal size. Meant 65A alternator. Was thinking of the one I built my mate for welding of his 4wD.
2.5hp motor from edger, 65 amp alternator and a diode in sense connection to drop the sensed voltage from battery so regulator sees 0.7v lower. Switch on box selects charge voltage.

Charges batteries at about 45-50A depending on state of batteries but on dc load test easily got 70A.

Hi Sparksy, good effort m8, I tried one with a 3hp b&s engine 30 odd years ago with no success. Looking at yours I can see that it is running at maybe 2:1 and I think that might have been my problem, geared to high. It is amazing how much power you need to get some amps out of an alternator. I tried this one at 1:1 and it just killed the 6.5hp motor, the ratio i settled on is about 1.8:1

Originally Posted by shedhappens

Hi Sparksy, good effort m8, I tried one with a 3hp b&s engine 30 odd years ago with no success. Looking at yours I can see that it is running at maybe 2:1 and I think that might have been my problem, geared to high. It is amazing how much power you need to get some amps out of an alternator. I tried this one at 1:1 and it just killed the 6.5hp motor, the ratio i settled on is about 1.8:1

I was hoping to build it like a christies and have the alternator direct coupled but your right , it didnt like too much load. Needs the revs to get the amps. We made a similar unit 30 years back to charge the glass 2v Telecom cells for navigation beacons when the solar couldnt keep up.

Originally Posted by shedhappens

If you have ever lived off grid you would understand the frustration of continually pouring fuel into a generator that is spinning over at 3000 rpm and often only pushing out a few watts, lots of fuel ($) and noise for little return.

Are you living off grid now John, or just prepping for the apocalypse? I’ve got a Honda EU22 on my shopping list because I foresee a long power outage in my future.

Hi John,

For some reason the forum won't let me respond to your later post !

The coil in this picture is the exciter coil. The remnant magnetism causes a voltage in that coil that creates a magnetic field in the rotor that induces a voltage in the field windings. Its this voltage that is rectified and used to provide the output voltage. The stronger the voltage generated by the exciter coil the stronger the magnetic field produced.


Replacing the voltage regulator would probably be the better way to go !

As far as ripple voltage is concerned if you are measuring the output voltage without a battery connected then you will also have a voltage ripple content. The regulator may say 24 volts but it will be higher than that for the reasons you have mentioned. I've set my solar charge controller to provide 14 volts, the maximum that it should be for a 12 volt Lead Acid battery.

Originally Posted by jack620

Are you living off grid now John, or just prepping for the apocalypse? I’ve got a Honda EU22 on my shopping list because I foresee a long power outage in my future.

G/day Chris, nah still have the power on. They did something to our power, supposedly upgraded all the mains for bushfire protection now the power goes out often and when it happens at night i wake up in a shock thinking my missus is trying to smother me with the pillow, actually the cpap stops pumping air into me.
Also we had that storm a few months back that knocked out power all around melbourne so i thought i would build a small shed and put a bit of a battery backup on the house, it operates the tv, poota, cpap machine, gas ducted heater, fridge and soon the evap cooler, so only a small system but also has pretty much killed the power bill. I have solar panels but have not hooked into that as yet, i have 2 small solar panels that switch relays for 2 battery chargers when the sun is shining so catch that power anyway.