2 grounds on 1 PCB, for 2 batteries connected in series - Page 1
Forum section: electronics / general

author: YoTech
author_rank: Contributor
timestamp: March 29, 2018, 10:17:19 am
content: My ideas is this. I know voltage is measured in paralel, so I have 2 batteries (12V each) in series. I connect 1 voltage monitor circuit to the upper battery's + and - (battery2). I connect the second voltage monitor circuit to the lower battery's + and - (battery 1). I need ground on the upper circuit and the lower circuit? The grounds must beseparated? Can this be done on a PCB? Say 1 layer, internal copper 1 is ground 1, and botttom copper is ground 2. Do I have to connect the 2 layers toghether (star them) andhow do I do it in KiCad?I am a bit unfamiliar with the ground concept! I know the ground is just a low resistance conductor (10 on -7 ohms) which attracts electrons. It has a low reference potential(and generators are always grounded for defence). But what the heck can a small PCB layer do? Is there any point of putting 2 grounds on 1 PCB even? Should I use blind vias ornormal ones? Whats the difference?Sorry, its not many questions, its 1 question with all the details combined as 1!

author: YoTech
author_rank: Contributor
timestamp: March 29, 2018, 10:33:03 am
content: Here is the block diagram of the entire PCB with 2 circuits for monitoring each of the batteries connected in series.Please read the picture text in this post!

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 10:58:50 am
content: You would consider 1 ground as ground, and the next as +12V, with the top units supply being +24,You can definatly create a ground symbol, however i would still be careful that you dont mix them up, fire, brimstone, magic smoke and all that.Simply connect a power flag to your battery - would equally work, there is no direct need to throw a ground symbol on it other than convenience, and have bat2+ / bat2- for the second circuit, if you left the bat2- / bat1 + an optional connection it may even give your circuit more flexibility and avoid current flowing through your board if a battery connection becomes loose.

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 11:09:57 am
content: To clarify your other questions, "Ground" is generally just a point on the circuit that most other things are referenced off. you pick it at a convienient point and so be it,Your circuit does not have to connect battery1 + to Battery2 -, Instead i would strongly recommend it is done outside of your circuit, If someone miswires something, you could have many hundreds of amps across your PCB.For such a circuit I would say it could easily be done on 2 layers, assuming your not doing much more,In kicad I would probably approach this design by copying the first batteries design, updating battery1 to battery2 on the designators, running the annotation wizard to assign new ID's to the new parts, and have them function as 2 independant circuits on the same PCB with no interconnections.In almost all beginner boards I would say avoid blind or buried Via's, simply because it costs more, (another hole plating pass)

author: VEGETA
author_rank: Super Contributor
timestamp: March 29, 2018, 11:13:58 am
content: I have a similar question, which is that I have a Li-ion battery pack and want to make 2-channel power supply with it (SEPIC design)... Can I make 2 isolated channels?This is so much similar to this post, since making 2 separate grounds is isolation. notice that I want only one battery pack as a source not 2.

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 11:42:30 am
content: to you vegeta, it comes down to your end goals, if you wanted both to be isolated from another, you would need an isolated switchmode powersupply for atleast 1 circuit, if you just want 2 rails both referenced to some common point, then it can be done without isolation.At a basis its different from the op, whose circuit can function as an isolated unit, and a misunderstanding led them to think it was required to link them,

author: VEGETA
author_rank: Super Contributor
timestamp: March 29, 2018, 07:48:30 pm
content: Quote from: Rerouter on March 29, 2018, 11:42:30 amI need isolation yes.So I can join them in parallel and series

author: YoTech
author_rank: Contributor
timestamp: March 29, 2018, 09:10:58 pm
content: So like this? With no ground and the 2 circuits being isolated from one another? Are the comparators a good idea for isolated circuits?What will happen when I filp the switch and the batteries are connected in series?Edit: These are 12V, 120A/h batteries.

author: ar__systems
author_rank: Frequent Contributor
timestamp: March 29, 2018, 09:15:49 pm
content: Yotech, given your little knowledge of electronics, I would caution you against experimenting with Li batteries. They will not tolerate any b$ on your part. Sorry, if I can't be of more help.

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 11:50:48 pm
content: yes yotech, thats a fair design,