Daisy chaining power cables - Page 1
Forum section: electronics / projects

author: Fulcrum
author_rank: Regular Contributor
timestamp: July 15, 2016, 08:16:35 pm
content: Hi everyone.I have to power 16 boards with various voltages (+6, -6, +17, +90). Both +17 and +90 lines will pull minimal current (a few mA at most), while the +6 and -6 both can pull up to 150mA.I would like to daisy chain the power cables, but I worry that I will have problems with loading effects. The last board in the chain will not only see a voltage drop (which can be mitigated by increasing the voltage from the power supply a bit), but are there other effects?

author: Fungus
author_rank: Super Contributor
timestamp: July 15, 2016, 08:59:17 pm
content: If there's any other wires going between the boards then you have the possibility of ground loops appearing.Other than that? Nope it's just voltage drop.You could connect the power to both ends of the chain. It's only a few extra wires and will halve the voltage drop (it will droop towards the middle of the chain).If the droop in the middle is too much then add an extra set of power wires there as well. Now your worst droop is much less and you only connected three sets of wires.

author: uncle_bob
author_rank: Unknown
timestamp: July 15, 2016, 11:33:22 pm
content: HiA daisy chain has one basic issue:Unplug one board and everything downstream dies ...That can make troubleshooting / servicing a bit of a pain in some situations.The obvious alternative is to star wire them to a distribution card. Same number of connectors either way.Bob

author: Monkeh
author_rank: Super Contributor
timestamp: July 16, 2016, 01:10:16 am
content: Quote from: uncle_bob on July 15, 2016, 11:33:22 pmNot with ribbon cable or feed-through IDC connectors (MTA100 series comes to mind).

author: uncle_bob
author_rank: Unknown
timestamp: July 16, 2016, 01:57:24 am
content: Quote from: Monkeh on July 16, 2016, 01:10:16 amHiWhich really isn't daisy chain. It's either a backplane or a rear harness. Daisy chain = into one, onto the board, back off the board, into another.Bob

author: Monkeh
author_rank: Super Contributor
timestamp: July 16, 2016, 01:59:55 am
content: Quote from: uncle_bob on July 16, 2016, 01:57:24 amA semantic but fair point. Same basic concept of not having a load of star wiring tangling things up, and fewer connectors to boot. Worth bringing to the OPs attention.

author: uncle_bob
author_rank: Unknown
timestamp: July 16, 2016, 02:01:28 am
content: Quote from: Monkeh on July 16, 2016, 01:59:55 amHiSince it's a pretty obscure point, who knows what the OP intended ....Bob

author: Fulcrum
author_rank: Regular Contributor
timestamp: July 16, 2016, 11:26:23 am
content: Quote from: uncle_bob on July 16, 2016, 02:01:28 amGood point! What I meant was indeed the daisy chain deal where power goes into one card, and out on the other side to the next card.

author: SeanB
author_rank: Super Contributor
timestamp: July 16, 2016, 04:20:32 pm
content: Easiest is a ribbon cable with a lot of conductors, and arrange it so the high voltage rails are on the outer wires, with at least 4 grounded wires inside so that a wrong connection does not put 90V on your 6V rails. Using a 20 way IDC cable and the matching pin headers means the power will be in at least 2 conductors , with some ground conductors between them. Tip is to use a polarising blocker pin on the IDC sockets on the cable and a missing pin on the board side, so connecting in reverse is not going to let smoke out. As well having 2 conductors will reduce voltage drop on the cables. You can either use a plug and socket with a short cable for each board, or loop through them all and put the IDC connectors along the ribbon cable, so saving on the need for 2 sets of plug and socket per board, just loop through and do not plug in any unused sockets, they will be fine disconnected.

author: bitslice
author_rank: Frequent Contributor
timestamp: July 16, 2016, 04:32:15 pm
content: Or put the voltage regulation on the end boards.Like a S100 box, powers the backplane with 8v and regulate to 5v on each card.

author: penfold
author_rank: Frequent Contributor
timestamp: July 16, 2016, 05:56:49 pm
content: You may have to consider how you're grounding the system, you don't really want to be daisy chaining the ground connection.

author: Fungus
author_rank: Super Contributor
timestamp: July 16, 2016, 06:01:19 pm
content: Quote from: uncle_bob on July 16, 2016, 02:01:28 amDaisy chain:https://www.google.es/search?tbm=isch&q=daisy+chain

author: bicc1306
author_rank: Contributor
timestamp: September 30, 2016, 03:02:03 pm
content: Daisy chaining power strips may be dangerous sometimes with extension cords.

author: Monkeh
author_rank: Super Contributor
timestamp: September 30, 2016, 03:10:49 pm
content: Quote from: bicc1306 on September 30, 2016, 03:02:03 pm...Is there a reason you're dumping unrelated pearls of wisdom in random threads?