hacking a powermax converter

[John Frum]

I want to add custom charge termination logic to a

PM3 24V Series - PowerMax Converters

PowerMax PM3 Series 110Vac to 24Vdc Battery Charger/Converters for 24V battery banks, Off-Grid, Trucking, Telecoms and powering 24V equipment

powermaxconverters.com

Here is my test report.
If anyone has a idea how to stop the fan from running full bore I'm all ears.

test 1:
    baseline:
        PM3-25-24LK powered up
        29VDC on dc terminals
    stimulus 1:
        apply heatgun to heatsink near thermistor
        wait ~300 seconds until green led goes off
    stimulus 2:
        apply cooling fan to heatsink
    observation 1:
        PM3-25-24LK green led goes off
        voltage drops to ~0
    observation 2:
        PM3-25-24LK green led goes on
        voltage climbs to 29VDC
        PM3-25-24LK fan does not turn on
    expected:
        as above
test 2:
    baseline:
        PM3-25-24LK powered up
        29VDC on dc terminals
    stimulus 1:
        put a short in parralel with the thermistor
        wait 60 seconds
    stimulus 2:
        remove short
    observation 1:
        PM3-25-24LK green led goes off
        voltage drops to ~0
    observation 2:
        PM3-25-24LK green led goes on
        voltage climbs to 29VDC
        PM3-25-24LK fan goes on full blast and doesn't turn off
    expected:
        same as above but fan should not go on full blast

 

[John Frum]

I checked again and the fan noise seems to be the same loudness in both tests.
I'm ok with the fan running constantly when I'm charging.

However... putting a relay in parallel with the themistor will defeat the unit's overtemp protection.
Will need to address that.... not sure how.

 

[John Frum]

so the lastest revision of the plan is...
Currently the system has one charge source which is the converter.
One main load which is the inverter.
Both go through an overkill 8s bms to the battery.
To this I will add...
A 2nd cheap jbd bms that is only connected to a normally open ssr
The normally open ssr is connected to the thermal control port on the converter
The BMSs thermistor will be kapton taped to the converter in the hottest spot to do thermal shutdown if required.
The new bms will have balancing disabled so that it doesn't interfere with the primary.
The converter will be set to constant voltage of 28.8volts which is 3.6 volts per cell.
The 2nd bms will be set to trigger at 28.4(3.55) volts high pack and 3.6 volts high cell.
It will be set to release at 26.0 volts and 3.2 volts per cell.
The high temp cutoff will be set to 105F to shutoff the converter in case of over temperature.

             new_bms->new_thermistor
             new_bms<-new_thermistor
battery.neg<-new_bms<-ssr<-converter_thermal_control
battery.pos---------->ssr->converter_thermal_control

 

[Bob B]

I'm following what you are doing .... even though I don't really understand exactly what you are doing.
Where are you running your code?

 

[John Frum]

I'm following what you are doing .... even though I don't really understand exactly what you are doing.
Where are you running your code?

There is no code, the 2nd cheapy bms controls the ssr which controls the converter by hijacking the converter's over-temperature protection.
Thats why I'm using the BMS's over temperature protection to to protect the converter.

I just use the code tags so that my ascii art is properly formatted.

 

[John Frum]

I think I made a thinko earlier.
I'm too tired to think but the intent is to have this solution be fail safe.
So I guess that means normally closed relay.
Too tired to think right now.

 

[time2roll]

With adjustable boost voltage why stop the charging early?
Or is the 24v not adjustable?

"Output voltage adjustable from 26.0 Vdc to 33 Vdc"

 

[John Frum]

With adjustable boost voltage why stop the charging early?
Or is the 24v not adjustable?

I'm running it in constant voltage mode.
It is adjustable and I want to set it quite high.
Constant voltage with proper charge termination will give a much better and faster charge.
With no unnecessary saturation.
The downside is no float but I'm more than ok with that.

 

[John Frum]

Another option...
Use this AC relay https://www.digikey.ca/en/products/detail/altech-corporation/SO963460/8546995
In this box https://www.homedepot.ca/product/carlon-thermoplastic-junction-box-6x6x6-in/1000403708

Pros:
Won't void the converter warranty by fiddling with the internals.
Don't have to re-engineer a thermal protection solution.

Cons:
Switching 15amps on 14 awg as opposed to milli-amps on 24 awg.
Have to use the box for physical security.
Mixing 120VAC and 24VDC in the same box.

Have I just moved the thermal problem to another component?
Will I need a heat sink?
Will a heat sink even be effective in a plastic box?

Need help from the community including @Hedges @Supervstech

 

[John Frum]

New topology

ac switching

dc {
    battery.neg<-new_bms<-ac_ssr.control.pos
    battery.pos---------->ac_ssr.control.pos
}
ac {
    outlet<->ac_ssr_switching<->converter.l
    outlet<-------------------->converter.n
    outlet<-------------------->converter.g
}

 

[curiouscarbon]

can you attach a digital potentiometer to the thermristor and then measure the temperature yourself and send a "semantic temperature"?

like, send the resistance for freezing temp or something.. when you want it to stop charging.. i'm not sure if it has under temperature shutdown in addition to overtemp

shorting it might make it think it's super hot or something and turn fans to max

Adafruit DS3502 I2C Digital 10K Potentiometer Breakout

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just random thinkin, hope you can figure this out.. fixed voltage with cutoff is really appealing for LFP

 

[John Frum]

can you attach a digital potentiometer to the thermristor and then measure the temperature yourself and send a "semantic temperature"?

like, send the resistance for freezing temp or something.. when you want it to stop charging.. i'm not sure if it has under temperature shutdown in addition to overtemp

shorting it might make it think it's super hot or something and turn fans to max

Adafruit DS3502 I2C Digital 10K Potentiometer Breakout

If you're a person like me that gets exhausted turning knobs all day, the DS3502 is just the ticket to calm all your knob-turning related troubles. Instead of having to turn ...

www.adafruit.com

Digital Potentiometer - 10K - COM-10613 - SparkFun Electronics

Potentiometers are incredibly useful, whether you're controlling the volume on your stereo or the 'mood lighting' in your room. The problem with traditiona

www.sparkfun.com

just random thinkin, hope you can figure this out.. fixed voltage with cutoff is really appealing for LFP

I hadn't thought of it but, it seems like an unnecessary complication since I've solved the control problem.
Also no temperature control solution is required for the ac switching option.