DIY - 1st Build Project (Wiring Diagram)

DIY Builds
1

Hey guys… thanks for the comments and tips regarding my battery cells.

My next step is to check my wiring diagram. I am using a BMS fo charging only configuration.

Also, there will be a DC/DC converter so I have a couple of USB ports for accessories.

Based in thousands of diagrams available and heaps of research, I came up with the diagram bellow.

I am pretty sure it is right. My only doubt is in regards the charging only sep up for the BMS. I’ve seen a couple of variations around.

Again, any comments or tip would be great appreciated.

Cheers

IMG_5556
IMG_55562448×3264 918 KB

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Add fuse between charge port and CH- and the rest look good. Consider not running sensor wires, or only running the GND (black) and TMP (white) sensor wires.

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Devil’s advocate: use your sensors until they die / cover them with conformal coating so they don’t :stuck_out_tongue:

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Your dcdc converter should be rated for at least 42v. 50v is probably better you never know if they can handle voltage spikes.

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Thanks mate… didn’t think about using fuse on negative side

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Thanks mate… plan is to use one rated for 60V… still waiting on the enclosure so I can check space availability

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Im curious why do you fuse the negative? Is it because the charge port has its negative side on the outside?

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Because positive is the “common” side based on the way BMSs are wired up.

You can put it on the positive side of the charge jack if you want, just as long as it’s there.

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Could you clarify why you want to fuse the negative lead and not the positive?
I always do it the other way, rather have the positive line cut then ground.

Edit: missed your last comment, still would like a better explanation tho xD Cutting positive from the outside world still makes more sense to me

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Usually you have a common ground in electronic circuits. You don’t want do disconnect the common ground so you fuse the positive wire.

With our BMS however all positive wires are connected and the negative wires are switched by the bms. @b264 continues this philosophy and fuses negative so all positive wires can stay connected.

In reality it does not really matter as long as there is a fuse I guess.

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Because the way BMSs are wired, I usually treat + as the “common” side and do all the fusing and switching on the negative side.

It’s only because of the BMS setup. If they were set up with a common B- and had P+ and C+ then I’d do it the other way around.

It really doesn’t matter which side of the jack you fuse, as long as the fuse is in series with the circuit.

:arrow_up: yep, this

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I mean, I’ve designed over 100 different kinds of PCBs for a variety of applications, automotive, medtech even BMS’s. I’ve asked the same question to more senior designers and they just scratch their head as well.

I mean, sure, In general It doesn’t matter as long as w/e caused the fuse to blow gets disconnected. But in the scenario that ground or supply is hanging out externally, I’d much rather have supply cut off since it could short against something else with lower potential. A good example is f.e metal housings or enclosures that might have PE.

There are also sevral standards pointing out that the device should have fuse on positive end :man_shrugging:
But I keep getting proven otherwise, especially with stuff from china. Boggles my mind.

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@b264 @linsus what A should a fuse be? I recon it must be higher than charging current, but how much?

My charger is 9A, so what amperage fuse should I put?

Thanks

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Depends how fast the fuse blows, usually u can draw 10A out of a 10A fuse all day(unless its a fast blow fuse). All manufactureres seem to define when a fuse blows differently, so its abit of a mess.

I had a return at work where someone drew 800A out from our 450A fuse for a few secs, the system overheated before the fuse could blow :man_shrugging:

10A fuse should do fine if your charger is 9A.

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What @linsus said is correct but I’d probably use a 15A fuse

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Thanks again everyone… making this project go smoothly. I am still waiting on some parts. But soon will start posting photos of the progress.

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I think it comes down to the differences between nFETs and pFETs really.

It’s really just longstanding convention and tradition that dictates “ground” is the electron-emitting side. This could have easily have been the other way around since way back in the day.

I agree that it’s always better to stick with convention if you can. But since china BMSs are essentially ALL wired with common positives, then I just adapt and wire all my china-BMS-containing devices that way as well.

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The reason I think you normally fuse positive is because sensors and data signals usually use the common ground. It’s better to cut positive voltage to not separate ground somewhere to not mess with the data of other circuits that might still run on another positive voltage.

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That’s absolutely true :100: if there is non-wireless communication/connection between the parts