Reducing the Current output of a battery charger

[ThermallyFrigid]

Hi guys,
I have a battery charger that is a 12v / 24v (auto select) charger that puts out 8 Amps at 12v and 4 amps at 24v

But that is too high for me.

I'd like at most 2 Amps @ either 12v or 24v.   I think ideally 1Amp output would be best overall.
I'm thinking resistors are the way to reduce current without reducing voltage but Not sure how to do it.
I can provide a full schematic if that would help?

Here is a picture if the internals of the charger and a list of the major components.

So how do I reduce the current on the output of both the 12v and 24v down to 1A ?

PS....
Not necessarily looking for an "exact" solution, but just in general and how roughly.

Thanks

[tunk]

Wouldn't really have a clue, but above the the two
capacitors to the left there's something that could
look like a current shunt. You could possibly try to
replace it with:
- either four times the length and same diameter
- or same length and half the diameter
Or it may blow up your charger.

[ThermallyFrigid]

Wouldn't really have a clue, but above the the two
capacitors to the left there's something that could
look like a current shunt. You could possibly try to
replace it with:
- either four times the length and same diameter
- or same length and half the diameter
Or it may blow up your charger.

That's the best suggestion so far.  I'll look into it.
Thanks!

[abdulbadii]

If it's really, frankly I don't know

but first we must ensure its claim is true by good, reliable, accurate MM

Read  the charger current when it's charging by putting the batt. on end to the charger the other popped up to open to be used for MM's probe to meter as in series with the other charger end.
if it requires 2 batt. to be viable to charging, put another batt in other slot or just short this slot

Read this current, really as the rate stated above ?

[BrokenYugo]

Does "motorcycle" mode not do something like that already?

[ThermallyFrigid]

Wouldn't really have a clue, but above the the two
capacitors to the left there's something that could
look like a current shunt. You could possibly try to
replace it with:
- either four times the length and same diameter
- or same length and half the diameter
Or it may blow up your charger.

Turns out the wire jumper/shunt measures less than .1 ohm so I don't think that will have anything to do with reducing current.

[ThermallyFrigid]

Does "motorcycle" mode not do something like that already?

Good question.
I hadn't tried that mode but if so you may be onto something.

But I can't right now because I have it torn down in the lab recreating the Schematic and PCB in KiCAD so I can make changes to suit my needs.

[ThermallyFrigid]

I'm thinking the way to do this is by adjusting the timing of the PWM cycle.

That would be done primarily by changing resistors (I believe).

This should be easier to figure out once I have the schematic completed.  There's gonna be some math involved.

[BrokenYugo]

I point out motorcycle mode because I assume the goal here is to charge small SLAs, which many motorcycle batteries are, I've seen them as small as 3-4Ah.

[ThermallyFrigid]

I point out motorcycle mode because I assume the goal here is to charge small SLAs, which many motorcycle batteries are, I've seen them as small as 3-4Ah.

When I put it all back together, I'll try that mode.

I makes sense.  Why have a "motorcycle mode" if it's the same output parameters as the full size car / truck battery?

[bdunham7]

Turns out the wire jumper/shunt measures less than .1 ohm so I don't think that will have anything to do with reducing current.

I think the point is that the shunt is used to measure the current, then that measurement is used to control the current, as well as display it.  So increasing the shunt resistance 2X would cause the charger to put out half the current, but probably not display that correctly. 

If you have a motorcycle mode, that should be 2A maximum. 

[ThermallyFrigid]

Turns out the wire jumper/shunt measures less than .1 ohm so I don't think that will have anything to do with reducing current.

I think the point is that the shunt is used to measure the current, then that measurement is used to control the current, as well as display it.  So increasing the shunt resistance 2X would cause the charger to put out half the current, but probably not display that correctly. 

If you have a motorcycle mode, that should be 2A maximum.

I can try that just to see.

[abdulbadii]

The only viable way is to acquire schematic by contact to the maker/seller or doing RE, get all componets specs.

Then if not experienced enough try to install and run LTspice (OS: all. On Linux need Wine), and simulate it around either the Voltage regulator or zener diode functioning to regulate output volltage as long as within certain R load range it is operating. Get this R range specs of the either regulator of output, by we know.. digging info,  googling.

Find R min of this R range, this would be the sum of R internal battery, original load, and another R load in parallel to the R batt. R.min <= R.batt || an R. Get this R =
1/ R >= 1 / R min - 1 /R batt

Apply the R parallel to battery, so that it will shunt and might reduce the current in original load ie. for battery, means get so many more the same type battery, calculate R.batt || of all them and charge them all parallel at once. Each has charge with decrease current going throuh i

In case haven't known how to get R internal batt,
Try meter batt DC volt and DC current it generates by quite good, accurate MM, and simply divide both in that order i.e. batt DC Volt / I

[DavidAlfa]

The only viable way is to acquire schematic by contact to the maker/seller or by RE, get all componets specs.

What?? You only need to find the shunt resistor. There's always a shunt resistor or current metering method.
Then, find the IC that measures this., the datasheet will show the drop voltage->current conversion formula, all you need is to calculate the new shunt resistor and replace it.

ThermallyFrigid, do you really think we can help you with only these pictures?
It's like if my engine breaks down and ask how to repair it showing a generic car picture
Make proper pictures showing the component markings, the bottom traces...
That modification is usually veryeasy, but we need to see how it's made.
I did the same few years ago to charge a small 7A lead acid battery with 5A charger.
Added a switch to lower the current to 500mA, worked nicely.