I'm sorry if this already exists, but I couldn't find anything on the forums.
I am wanting to do a project whereas I use an Arduino (which specific one does not really matter as space isn't that big of an issue) to monitor the voltage of 2 or 3 li-ion drill batteries (I'm using 18v Milwaukee) and have it control relays to drop in or out batteries as the voltages vary in a parallel circuit.
I understand that if the batteries parallel that the voltages will stabilize through back charging, but when initially paring if the voltages are too far apart it will crate a high current scenario, becoming potentially very hazardous, or having the battery not parallel at all. I would like to make it simple to use for someone who is unaware of this possibility, hence the voltage monitoring. I also understand that batteries depleat at different rates, and is possible that there will be enough of a difference in voltage at some point that it may be required to drop a battery out of the circuit as well. Overcurrent devices will also be in place, but that can be a separate standalone circuit, and also there are built in transistors with current sensors on the batteries themselves.
I plan on 3d printing a dock with 2 or 3 battery slots (or more, who knows
In short, I would like to have it sense the voltage of the first battery, and if within a volt, then energize a relay to parallel the battery into the circuit. I am a certified electrician, so the wiring and hardware are not an issue for me, and appropriate safety precautions.
I have tried the voltage readout example and have had it display the voltage serial readout using the simple voltage sensor 0-25V.
I have no idea where to start with the code to use these numbers as a reference to energize a relay based on a second voltage reference
duder56:
In short, I would like to have it sense the voltage of the first battery, and if within a volt, then energize a relay to parallel the battery into the circuit. I am a certified electrician, so the wiring and hardware are not an issue for me, and appropriate safety precautions.
I have tried the voltage readout example and have had it display the voltage serial readout using the simple voltage sensor 0-25V.
I have no idea where to start with the code to use these numbers as a reference to energize a relay based on a second voltage reference
Do I understand you that there is one battery connected to a circuit and if the voltage of that battrery and the spare battery are withing 1 volt, add in the spare battery as a parallel to the first using a relay?
Paul
If the batteries are wired in parallel, how could they ever become differently discharged? And if they did, how are you proposing to test or detect this?
Also, 1 volt difference seems like there would still be plenty of, um, excitement when you snap them together.
My only experience with parallel cells is with smallish lithium polymer battery and the recommendation is to keep differences before connecting to under 0.1 volts. I usually can do much better, obvsly the lower the safer.
Watching from a distance… I think I’d cover the desired function by just switching in and out one battery from a number of them as required. Unless you are trying to get a higher current, in which case I’d just get an appropriate ly powerful battery.
duder56:
If it is within reason I'd also like to do an additional 2 or 3 batteries? And thank you for the quick response Paul
Then continue with the engineering by determining the current requirements for the project and get a relay that can handle the current and have a winding voltage rated for the battery voltage. You will need a MOSFET to switch the relay circuit from your Arduino.
While you are doing that, decide on a plan to turn this all off. So far, you have only been connecting things.
And also, get fuses to handle overloads. But you already knew that!
Good luck,
Paul
1v on a 3.7v cell is a lot, 1v on an 18v series parallel pack, not so much, and 1v was a starting point, could go lower if I can manage to make this work.
I understand that I need switching MOSFETs for the relays, thank you for the suggestion! And turning on and off isn't an issue either. I am just looking to make the portion of it to parallel these batteries together safely without metering equipment, handled by the Arduino checking the appropriate voltages, that way if I'm not available to check everything someone else can remove one of the drill batteries and slot in a new one without having to check everything, and no interruption of power. It will be a multi purpose system, powering many differt things (not all at once mind you) with buck and boost converters in play, just using the batteries as the power source.
Paul_KD7HB:
Do I understand you that there is one battery connected to a circuit and if the voltage of that battrery and the spare battery are withing 1 volt, add in the spare battery as a parallel to the first using a relay?
Paul
alto777:
If the batteries are wired in parallel, how could they ever become differently discharged? And if they did, how are you proposing to test or detect this?
Also, 1 volt difference seems like there would still be plenty of, um, excitement when you snap them together.
My only experience with parallel cells is with smallish lithium polymer battery and the recommendation is to keep differences before connecting to under 0.1 volts. I usually can do much better, obvsly the lower the safer.
Watching from a distance… I think I’d cover the desired function by just switching in and out one battery from a number of them as required. Unless you are trying to get a higher current, in which case I’d just get an appropriate ly powerful battery.
a7
I would like to not have to buy more batteries and make use of what I have available, which is a boat load of Milwaukee batteries, some of which are older with somewhat reduced capacity, and also different styles with lower amp hours. So they might discharge at different rates.
So for example, I have a cooler 12/24v compressor cooler, and I have tested it with a buck converter down to 12v and it will keep it at 2°C for roughly 8 hours off of a single Milwaukee battery, but let's assume I'm away from the campsite for longer, or when I left it was already half discharged. I'd like for a multi battery system so that I don't have to worry about it for a full day or 2 even.
My other option is running the batteries in series, and then using a buck converter down to 12v, but when you start doing that you limit your available wattage considerably due to electronics constraints.
So the intention of the project is to produce a device, to be used by those with little or no knowledge of high current batteries, which then will allow them to 'safely' use a variety of maybe recycled batteries as a 'reliable' and 'safe' power source ?
Its a big ask to make such a design foolproof and do remember real bad things can happen with high current capable batteries.
srnet:
So the intention of the project is to produce a device, to be used by those with little or no knowledge of high current batteries, which then will allow them to 'safely' use a variety of maybe recycled batteries as a 'reliable' and 'safe' power source ?
Its a big ask to make such a design foolproof and do remember real bad things can happen with high current capable batteries.
Good luck.
I appreciate the concern, but the intention was not to distribute the project to my friends and family unsupervised, more so that it will be in my possession, but if they needed to swap a battery they can do so. Also it should be noted that these batteries are not recycled, I just possess about 12 or so Milwaukee batteries from the tools I have purchased over the past few years, my "oldest battery" is probably around 3 years old.
Milwaukee batteries have on them an overcurrent/overvoltage/undervoltage protection circuits, so if there was to be a short circuit event (for which I would have also fused for regardless) the transistors on the board open up cutting off current flow. If I were to try and parallel two batteries with a big difference of voltage, there would be a very brief high current, making an arc, degrading the terminals, but not enough current would be allowed to pass to cause enough heat to explode the batteries.
But I still wish to make this circuit to avoid potentials like this, and the degradation of the terminals. I am also going to integrate a seperate overcurrent and undervoltage protection circuits because I wish to keep my batteries in good condition.
@duder56 your duplicate post in the Programming section has been deleted
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As general rule for parallel batteries, NEVER place different types and models in parallel, especially with Li-Ion ones ... it will easily end with a "KABOOM" device, more than with a battery pack ...
As industrial level, when Li-Ion cells are paralleled (like as example in notebook battery packs), not only they are all from a single model and producer, but also selected from a single production lot ... there is a good reason for this ...
Seems like this would include by implication advice to not parallel batteries at different points in their life cycle, no matter how identical they may have once bee.n
Advice often included in the instructions we throw away for battery operated devices, although they are speaking of not using batteries in series of different ages or types.
Is there no possibility of simply turning things off, switching batteries, however, then turning things back on again?
Series connections can be risked (cause is still a risk, with Li.Ion cells), with apposite balancing charge / protection boards ... but in parallel, also the manufacturers say to never use different cells, and always choose new and same production lot ones ...
Common batteries can be a bit dangerous if something go wrong, also if usually just become ruined or leak acids ... but Li-Ion ones have the bad abitude to blow and/or explode, in these cases ... ethyl ether (that is the solvent normally used in the cells for lithium compounds) is explosive enough if overheated ...
Have you considered running the batteries in parallel, with each going thru a diode, so that only the battery with the highest voltage at any particular time is the one supplying current?
This schottky diode for example, rated for 25V, 10A, you would lose 0.46V across it at high currents, with 18V battery pack that could be okay. https://www.digikey.com/en/products/detail/stmicroelectronics/STPS10L25D/603763
If you want to monitor all the batteries, use a voltage divider at the battery pack output before feeding into the diode to bring it down to a level that a 5V or 3.3V device can read.
