How to switch a 2v load using 3v Signal

Thread Starter

mdm183

Joined Jan 19, 2022
1
Hello guys

New here. I am trying to work out what would be the best way to control a 2v load using something like an ESP32 (3.3v)

So what i have is:

-------------
| BATTERY | (1.5 - 2.2v) ---> something?? >>> Resistor
--------------- ^^
| ESP32 |

I would of used the standard relays but can only do 10A. I need something that can support upto 30A of current.

I am designing a battery balancer, therefore when required to discharge some current, the ESP32 would turn on the resistor which would start draining the battery.

I have the correct resistor with the correct wattage rating (50w) . I just need to know what i can use for this. Very confused.

The load would be between 1.5v to 2.2v and the control voltage of the ESP32 / Raspberry would be 3.3v

I was looking maybe at a mosfet to replace the resistor and have the capabilities to control it too but i am stuck and not sure.

I implemented this for a 12v battery and that was fine as the relays did a perfect job (inside the 10A thresholds)

Many thanks for reading and any input would really help and unblock me :)

Cheers!
 

LowQCab

Joined Nov 6, 2012
1,915
Now I'm confused .........
What exactly are You trying to build,
and why does it need to be controlled by an ESP32 ?
.
.
.
 

dl324

Joined Mar 30, 2015
14,307
Welcome to AAC!
Very confused.
It shows. Your request is unintelligible.
The load would be between 1.5v to 2.2v and the control voltage of the ESP32 / Raspberry would be 3.3v
Loads aren't typically specified as voltages because with a series resistor the voltage drop across the load depends on the load resistance and the applied voltage.

As microcontrollers can't sink or source more than 10's of mA, the voltage of the control signal isn't important if you switch the load low side. Just use a logic level N channel MOSFET that can handle the currents involved.

What is the nature of this battery that the voltage is 1.5-2.2V and it can source up to 30A?
 

Irving

Joined Jan 30, 2016
2,531
Why oh why design a passive balancer for that sort of current? I'd like to see what your overall block diagram looks like.. And why are you balancing at 30A anyway? Normally you balance at the top of the charge curve when charging current has dwindled to a low level. Balancing any other time is pointless...
 

MisterBill2

Joined Jan 23, 2018
11,580
"Passive balancer?" I have not come across that term previously that I can recall. (post #4)

And the term "control a 2 v load is ambiguous. Do you mean switch the power on and off? Does that mean power the load??
 

MisterBill2

Joined Jan 23, 2018
11,580
A transistor of any type carrying 30 amps is going to need some heat sink and a means to assure that it is fully switched on. That is a big deal and quite a bit is important. And for charge balancing, why discharge at a 30 amp rate? Ten amps will do the job, just a bit slower.
But for switching a full 30 amps there are the automotive cube relays rated with 30 amp contacts. But they have 12 volt coils and so you will need a driver transistor and a 12 volt source to power the relay.

And why is an answer coming from other than the TS? Both "computer engineers". Something is funny here. Is it the same person with two user accounts????
Something does not seem at al right here!!
 

Irving

Joined Jan 30, 2016
2,531
Um, lead acid maybe?

Bob
Lithium Titanate

"Passive balancer?" I have not come across that term previously that I can recall. (post #4)
Most BMS do 'passive balancing' - ie bypass the higher voltage cell(s) and partly discharge them wth a parallel resistor while continuing to charge the stack.

My BMS's do active balancing - the higher voltage cell is connected to a boost converter that absorbs energy and returns it to the stack reducing the external chrging current so nothing is lost as heat - more efficient and quicker, though more complex.

Most big EV stacks now use active balancing...
 

MisterBill2

Joined Jan 23, 2018
11,580
OK, now I see the intention, although not the rationalization, for such a system.
How many cells would be in the series string of cells? What is the available charging voltage and current?
And it seems that there are some alternatives available that do not involve wasting any charge energy.
Charging individual cells separately could be an interesting and very effective scheme, although it would be a bit more complex.

I am wondering if this would be a design for a product, or is it for a one-off personal battery system?
 

Irving

Joined Jan 30, 2016
2,531
Charging individual cells separately could be an interesting and very effective scheme, although it would be a bit more complex.
I designed & built one for an 8S system, 3.6v @ 25A/cell. Its a bit more complex because each charger has to be isolated. I had a 24v feed and 8 identical flyback buck converters 24v->3.6v with a dedicated 1-cell LiFEPO4 charge controller and an overall control MCU with a TI BQ76930 battery monitor.
 

MisterBill2

Joined Jan 23, 2018
11,580
I designed & built one for an 8S system, 3.6v @ 25A/cell. Its a bit more complex because each charger has to be isolated. I had a 24v feed and 8 identical flyback buck converters 24v->3.6v with a dedicated 1-cell LiFEPO4 charge controller and an overall control MCU with a TI BQ76930 battery monitor.
Was the controller able to adjust the charge to each cell as needed?? Did it work well? Please let us know.
 

Irving

Joined Jan 30, 2016
2,531
Was the controller able to adjust the charge to each cell as needed?? Did it work well? Please let us know.
Each cell charges independently and tracks its own 'charge in'. The overall controller tracks 'charge out'. Since all cells are discharged at the same rate it handles partial charging well, as long as it get brought to full charge once in a while to realign everything. Its a 200Ah pack that gets discharged 20 - 40Ah a day so needs a full 9 hour approx return to 100% about once a week.
 

MisterBill2

Joined Jan 23, 2018
11,580
Each cell charges independently and tracks its own 'charge in'. The overall controller tracks 'charge out'. Since all cells are discharged at the same rate it handles partial charging well, as long as it get brought to full charge once in a while to realign everything. Its a 200Ah pack that gets discharged 20 - 40Ah a day so needs a full 9 hour approx return to 100% about once a week.
I wonder if the system described is more complex that the discharging resistor system that the TS is attempting to create. IT would certainly be more efficient.
Will the TS be interested in the details of the system, I wonder.
 

Irving

Joined Jan 30, 2016
2,531
Coming back to the TS original request, there's nothing intrinsically difficult about balancing, just the current he wants which is problematic and unnecessary. This circuit works well, balancing at 1A as shown, but will go to 7A without a heatsink, dissipating 24W in the resistor and 1.4W in the MOSFET. 30A requires a substantial heatsink @ 24W as well as 73W in the resistor so dumping 100W which is a hugely inefficient and unnecessary waste.

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