Ground Plan for Multiple Voltages?

[luvrbus]

Aren't all these new huge windmills across the country DC like the ones from the past ?

[eagle19952]

My question would be this...if you do not ground the DC to the chassis where else would you ?

[Lostranger]

My question would be this...if you do not ground the DC to the chassis where else would you ?

Dedicated, heavy-gauge wire ground loop for each house voltage. Tap the loop at any point where I need that voltage.

[Seangie]

Jim - you can safely ground everything to the frame of the bus.  As I said in a previous post -  I would run a direct line from the negative (ground) of the 12v or 24v supply to a block and then ground the block to the frame. Make sure your 12v and 24v Batteries both have a direct fused connection to the frame of the bus (ground/return path for DC). 

As far as wire size - blue sea makes a great app for your smart phone where you put in any combination of watts/amps/volts/length etc and it calculates fuses and wire size.

Have fun

-Sean



Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Len Silva]

One thing to keep in mind here is that the AC chassis grounds are not normally carrying any current, they are just safety grounds in case of equipment failure.  DC circuits, 12 or 24 volts, the chassis ground is carrying current and it is not always the best conductor, thus the suggestion that you run a copper home run return from each load.

BTW, the reason for DC power transmission on the west coast is that the distance from Bonneville Power to the Los Angeles area is 1500 miles, the half wave length of 60 Hz.  If you know anything about antennas and wavelength, that is the zero crossing point, thus very high losses.
(I did some work at Bonneville years ago and that's the explanation I got from the engineers).

[Lin]

I have no expertise to back this up, but the way I see it is that there is no problem with grounding multiple electrical voltages to the chassis.  That's what we have had on both buses and what it is the overwhelming norm.  Electronics are a different story; small variations can cause large changes.  Hence, as LRB mentioned, engine and transmission computers use isolated circuits.

[Lostranger]

I would run a direct line from the negative (ground) of the 12v or 24v supply to a block and then ground the block to the frame. Make sure your 12v and 24v Batteries both have a direct fused connection to the frame of the bus (ground/return path for DC). 
www.herdofturtles.org

Sean,

To be sure I'm understanding you, are you saying to ground each battery bank to the chassis through a fuse AND ALSO run a ground wire to the negative side of a fuse block WHICH IS ALSO grounded to the chassis?

Thanks for all the input.

Jim

[brmax]

I would chime in to mention some info if I can just put it out there and some of you can take off with it.  Some of these I worked with in the past a bit, anyway Each component has to be considered separately, Lets understand converters some are not isolated themselves and thus have a floating ground these should not use the same general frame as I understand because even dc is powerful.
terms like isolate, home run, J1939, CAN, Multiplexing are all way out there, and were there.
the AC grounds need some "nec" answers wayout of my league
The newest 01 up mostly ecms, atms, bdms are needing isolated grounds (home runs) because they - hold on now CAN use the same wire to do different things on a vehicle using a system called multiplexing via J1939 protocol, to top it off these voltages might have hi sides and low sides.
Again Im interested in working through this with you all as there are many many sharper knives here than me.
Just wanted to send this out there
Good day everybody

[Tony LEE]

Nope. DC for long runs....Im sure its out there in Google land somewhere.  

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

My understanding is that DC is used primarily for high power undersea links that aren't too long. Because an AC line has too much capacitive coupling between the phases in such small-diameter cables so losses are higher than for DC which has only resistive losses.

http://en.wikipedia.org/wiki/Pacific_DC_Intertie has a bit on this tie line ande they say skin effect is one deciding factor, plus the ease of connecting two non-synchronised power systems.

DC is the European standard

for what?

[Seangie]

Sean,

To be sure I'm understanding you, are you saying to ground each battery bank to the chassis through a fuse AND ALSO run a ground wire to the negative side of a fuse block WHICH IS ALSO grounded to the chassis?

Thanks for all the input.

Jim

Jim -  that is correct.  Not totally necessary as it is common to ground the negative to the frame (which supplies a return path to the 12v battery that is also grounded to the frame) and not have a seperate run for the negative on a DC circuit.

To compare the 2 -  In an AC circuit you have a hot wire (black), a neutral wire (white) which both go back to the panel (connected to the "source") Then there is a "green" ground that connects to the frame of the appliance or device requiring power.  This green wire carries excess voltage (in case of a short) back to the panel then to the ground. In an RV the ground will be bonded to the neutral inside the generator or bonded to the neutral somewhere beyond the pedastal at the campground.

In DC if you want a true ground (like you would have in an AC circuit) you would have a positive wire (red is typical), a negative wire (unfortunately black is typical although yellow, orange or blue can be common here) and then you can run a seperate line grounding the device to the chassis (green) that could carry any additional voltage back through the frame and because we don't have an alternating current it would just be carried back to the negative connection on the battery. If you think of the negative in a DC circuit as neutral this is where you would be "bonding" the ground and the neutral.

The DC current would take the return path of least resistance (the wire that is directly run to the negative on the battery) unless there was a short in the device or wire in which case the return path would be the chassis of the bus.

If you had breakers or a fuse for your DC circuit they should "pop" if there is a short as there would be no resistance in a short circuit and the amperage would shoot up.

I reccomended fusing the negative side of your batteries based on past conversations with Sean Welsh who made some really good points as to why.  You'll have to dig up previous posts to read those details.

Know that most of my DC circuits including the bus circuits are all grounded to the frame and do not have a return wire.  Also the positive side of my batteries are fused, not the negative.  I should practice what I preach but it takes time and money for that as most of my DC stuff was done before I got the bus.  Know that it is on my to do list to update this.

I hope that is not too confusing.  I do agree with previous comments that there are some devices that need their own circuit but in the DC world that circuit is typically designed into the device itself as anything battery operated (12v, 24v or on an alternator) will be operating in a system that has fluctuating voltages.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Seangie]

Oooops...double post

[RobSedona]

OK confused here LOL

What size fuse should I but in the Neg side of my 12v and 24v systems ??

they have always been straight to ground

will have to but this on the list of to do

[luvrbus]

Wasn't it Lucas the Prince of Darkness that fused the ground on some of the British cars and bikes,I have heard the argument for years on fusing the ground and installing the relays on the ground side both pro and con.

Richard (Driving Mrs Lazy) had every relay on the Eagle on the ground side Sonnie and Mike worked for weeks trying to make the systems work Sonnie replaced all the relays to the + side so I guess it gets down to preference 

   

[Lostranger]

Here is one past discussion on grounding the negative side of the house battery bank: http://www.busconversions.com/bbs/index.php?topic=22290.msg244760#msg244760 (http://www.busconversions.com/bbs/index.php?topic=22290.msg244760#msg244760)

Sean makes a potent argument. One of the last posts in the referenced thread offers several links to related threads on this board. I have not looked at any of those, but I'm sure they include gems.

Based on what I've learned, I believe I will put my catastrophic fuse on the ground side of both house battery banks. On the 24v bank, that will mean connecting a type T fuse to the last battery in pack. At the other end of the fuse holder I plan to connect both the inverter negative lead and a ground strap to chassis. Plan to do same with 12v bank, but no inverter connects to it. Ground/fuse/strap to chassis.

Does this sound reasonable to those who know? Any recommendations on fuse sizes? 24v battery bank is 490 amp/hours. 12v bank is 245 amp/hours. 2/0 cable all round.

Thanks again for the great discussion.

Jim

[Lostranger]

This link on battery info has been posted before, but it couldn't hurt to make it available again: http://www.batteryfaq.org