In general, as someone posted, the fusing should be to protect the wiring, unless it's a fuse for one specific device that has a lower current capacity than the wire that brings it power. There are well documented standards to follow, just look up charts like this: http://www.cerrowire.com/ampacity-charts Note it only goes down to 14 AWG and you may have some 16 or even 18 AWG. If you want to get into techie details something like this will boggle your mind (scroll down for a more geeky table): http://www.powerstream.com/Wire_Size.htm ...at the bottom of the page is even a voltage drop calculator. Speaking of which, power loss tables are also useful for low voltage DC systems like in our boats. For stuff drawing only a couple amps or less, not a big deal. But if you have a heavy draw far from your battery, you can start losing significant amounts of power in wire loss if your wire is too small (and if it's way too small you get risk of enough heat to melt something or start a fire). Here's some typical charts for different voltages, showing max wire length for 5% or less wire loss: http://www.solar-electric.com/wire-loss-tables.html The last table, for 12V DC, indicates that if you have a 6 amp draw, the longest run under 5% loss with 14AWG wire ("14 gauge") is 14 ft.; with 12AWG you can go 22 ft. with no more than 5% loss, and so on. A good way to find info on low voltage DC wiring, if not marine specific sites, is anything to do with the DC aspects of off-grid solar power systems. cheers, John S. On 02/20/2016 12:36 PM, Jazzy wrote:
I'm thinking the biggest things that may ever go in the lighter plug is a little inverter or a pump to blow up an inflatable. Maybe I should fuse that switch a little higher? On Feb 20, 2016 12:34 PM, "Keith R. Martin" <keith.richard.martin@gmail.com> wrote:
Yup sounds like you are okay depending on what you plug into the cigarette lighter plug...
I would be surprised if the gps plotter and a couple of usb devices combined exceeded 3-4 A, the lighter plug however is often used to power devices that draw a little more current, but 6-7 amps of a lighter plug is a pretty good load..
The good think is your meter will tell you..... The worst that can happen if it's properly fused is it blows with too large a load drawn from the lighter plug...
Keith
*Keith R. Martin, P.Eng.*
*Burnaby, B.C. CanadaSerenity,** M17 Hull #353*
On 20 February 2016 at 12:21, Jazzy <jazzydaze@gmail.com> wrote:
Hi all, Keith, never too late for a party! With led lighting and an older small grayscale gps/plotter, 1 cigarette lighter plug, one dual usb plug I'm thinking I can't really draw enough to cause an issue. Is this a correct assumption? I don't have official specs on what the items draw, just seems minimal to me even with everything on On Feb 20, 2016 12:16 PM, "Keith R. Martin" < keith.richard.martin@gmail.com> wrote:
Late to the party but I concur with Mitch and John's last post...
*1. Power supply (battery) to “+” and “-“. Disconnect the battery from everything else. 2. Connect “+ load” and “- load” where the battery used to connect.*
Attached I think is the picture John was talking about showing a practical wiring connection for the device in lab bench setting.
I would definitely put an inline fuse on this, and given the low cost of the device if it were me I would limit the fuse to 10A .. Given the low cost of the device, if you think you need more than 10A on the boat I would have a hard look at the device to make sure it could safely sustain the higher currents.
Keith
*Keith R. Martin, P.Eng.*
*Burnaby, B.C. CanadaSerenity,** M17 Hull #353*
On 20 February 2016 at 11:46, John Schinnerer <john@eco-living.net> wrote:
Ditto that...
Note that the diagram says "built in shunt" - this means that the device itself contains a thingamajig doohickey (sorry for all the technical terms :-) called a "shunt" that all DC power passes through on its way to the loads (and is what enables the measurement of the current).
So just connect as the pictures show, battery + and - to battery, and then you need to substitute your panel + and busbar - for the + and - of the big wire-wound resistor DC load shown in the pictures.
Absolutely fuse it, between battery + and meter +. A regular ATO or Mini auto fuse inline holder will do. As someone already said, fuses are to prevent fires mainly, protect the wiring from getting hot and/or melting.
Also, if you're in saltwater environment mostly, don't expect this cheap of a meter to last long.
cheers, John S.
On 02/20/2016 09:00 AM, David Rifkind wrote:
On Feb 20, 2016, at 9:24 AM, Mitch Carnes <
mitch_carnes@sbcglobal.net
> wrote: > > + to positive side of battery, - to negative side of battery. This > will power unit AND monitor battery voltage.+load to positive side of > battery - load goes to positive side of device being powered. (AMP/Current > meters are typically wired "in line" or "in series" of device being > monitored) The negative, or - side of the device being monitored still goes > to the negative side of the battery. >
I don’t think this is right. Look at the photos in the eBay listing and you can see they have hooked up:
1. Power supply (battery) to “+” and “-“. Disconnect the battery from everything else. 2. Connect “+ load” and “- load” where the battery used to connect.
It might not hurt to put an inline 20A fuse in the + line between battery and meter. Just in case.
-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com
-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com