Is there any reason why I cannot or should not connect multiples of these in parallel?
The reason I ask is for a model-train project where I need to make 12 volts available at up to 3 amps. I am already using one of these boards with a 12v step-up board off the 5v output for use in a Battery-DCC system for model trains, but I need a set-up capable of delivering 12v at 3amp.
Hi Martin
For a start 2 of these in parallel will not produce 12V. It will be the same voltage as one on its own.
Connecting power supplies in parallel requires the use of diodes anyway and there are always conflicts as both have to be EXACTLY the same voltage or the higher one finishes up picking up the majority of the load.
Secondly there are some smart bits in there like charge controllers, boost converters etc. So I don’t think connecting multiple units together would be a good idea. You would have to connect in series to get 12V and you probably run into grounding conflicts, especially if the grounds are not isolated which I think would be the case. Depending on just what you do and the device configuration you could even finish up with a short on one of them.
I think best forget that idea.
I think 12V at 3A warrants a separate supply. Even if you did connect these devices to get 12V you would only have the same current of one of them. Think about it.
Cheers Bob
To add to what Bob has said, while you could hook them up in parallel with diodes, the amount of current that you would need from a 5V system to boost up to 12V is going to be fairly high.
Is battery power 100% necessary? Or is mains power available where you have your project setup?
I should clarify that I was asking if they can be set up in parallel and then fed into a voltage step-up board to get 12volts.
I am currently using a single one of these with a step-up board, but the application only requires 12 volts at 500mA.
The 12V at 3A is to power a large-scale decoder, where the motors do regularly draw between 2A and 3A, depending on load, hills and curves (track conditions).
Grounding is not likely to be a problem since the two boards are mounted on an insulated base (MDF).
It is to set up battery power for an O gauge model locomotive, and yes it does need to be battery. However, the current draw will not always be 3amp, as the controller chip is rated to output up to 3amp for the motors (which each draw 1.5amp, and sometimes a little over).
Hi Martin
That is what I stated above. To properly share the load the supplies have to be EXACTLY equal or the highest will pick up most of the load and will not share until this supply drops its voltage to suit, at this point the supply is being stressed possibly beyond comfort.
Parallel supplies are used in a hot standby situation where if one supply fails the other will carry on. I have used 3 supplies in this manner BUT EACH SUPPLY has to be capable of taking the whole load so there is very little “sharing” taking place.
So no I personally don’t think this is really practical. Even if you could adjust each supply so they do share the current requirement by adjusting individual voltages there is really no guarantee they will stay that way over a period.
To clarify this.
The other consideration would be 12v @ 3A = 36W. at 5V this is 7.2A. Allowing for 85% conversion efficiency this would be 8.5A. This is what would be required at 5V. If we get down to say 3.7V battery level the same thing would apply.
5V @ 8.5A = 42.5W. At 3.7V this is 11.5A. Using the same 85% efficiency this requirement becomes 13.5A.
This looks pretty horrible and it is. If the converters in use do better than 85% (I only used this as a typical conversion efficiency figure) this situation improves a bit. There is a very true saying that applies here. you always get out less than you put in. You cannot possibly get more.
Cheers Bob
In the past I have used Battery Holder - 2x18650 (wire leads) to give me portable 5V power (used with a voltage regulator) you could look at wiring 2 of these in series to give you a 4S configuration (14.8V nominal voltage).
You wouldn’t be able to charge the batteries in the holder and would need to remove them, you would also need to look at the discharge rate of the batteries, typically for an 18650 they will have a constant discharge rate that will be noted as something like 1C, in the case of a battery that has a discharge rate of 1C and a capacity of 2600maH, it would be able to output 2.6A for an hour. You would need to ensure that the batteries you use are up to the task of output the current you need.
Thanks. Looks like for the 3-amp set-up I’ll have to make up a custom battery pack with its own BMS.
It would have been nice to find an off-the-shelf product, but I suspected that it might not work (hence why I asked here).
Hi Martin.
How about start with a 12V battery and convert down to any required lower voltages. The 12v battery could be lithium or even lead acid may be more economical.
Maybe this approach would be easier and more viable than trying to boost up from lower voltages.
Charging lead acid might be more attractive cost wise as well.
Tip: Do not consider an automotive battery for this type of application. A deep cycle Gel or AGM type would be more suitable and come in a variety of capacities.
Cheers Bob
Note I think Core actually stock 12V lithium batteries with built in BMS of various capacities but not cheap. The charger for said batteries is not cheap either.
I may have to put together a 4S battery pack with 26650 LiPo batteries rated at 5,000mAh.
I have a pair of Atlas F9 diesel locomotives which I intend to run as a permanently coupled set and there would be more than enough room inside them to put these larger batteries. The Mabuchi Motors inside them can draw up to 1.5 amps each - and these are much lower draw than the original 1970s motors!
Hi Martin.
I did not realise the batteries are inside the locomotives. This is the first mention of that.I thought the 12V was external.
How many motors are being driven from each battery. You might find that 5000mAh might be sailing a bit close to the wind at a 3A discharge rate you were talking about earlier. Not too sure of the actual numbers with lithium but that Ah rate quoted might be at the 20hr discharge rate. At higher rates (with lead acid anyway) the Ah rating reduces as the discharge rate increases. As I said I am not sure about lithium (I will try to look it up tomorrow) but lead acid reduces quite dramatically as the current draw increases.
I suppose it all boils down to how long do you want to run these locos and how many charge cycles you want out of the battery. I don’t suppose that discharging at a rate in excess of 0.5C continuously would be consistent with long life.
Cheers Bob
Core have a 12V 8Ah lithium battery with built in BMS and protection etc. Have a look at it SKU ASL4541A. It might fit your space and everything is done in the same package. Also should have enough grunt for your job.
The plan was to operate the two Atlas F9 units as a permanently-coupled pair using a DCC Sound decoder rated for 3amps. Looking closer at the project, it will probably work out better to kit them out individually with decoders rated for 2amps.
Hey @Robert93820, @Martin286410,
Can confirm Bob’s previous post;
This trend/behaviour is consistent with Lithium Ion Batteries. Here are a couple of articles with some data regarding discharge rate and capacity:
I would also like to +1 the suggestion to go for a higher voltage and step down, and would be happy to help select a product from our catalogue if necessary!
Hi Martin, Zach
Refer the link Zach provided above . I copied this bit out of the top link.
In particular the 3rd line down re high load and full discharges.
I have been advocating this sort of thing for a long time. If you want reliability and some longevity work out what power you need then DOUBLE IT. This reduces undue stress on a supply and allows a bit of head room for things you have forgotten and want to add later.
Cheers Bob
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