Ground Plan for Multiple Voltages?

[brmax]

Thanks Jim and everybody for sharing there input and the topic is very helpful, Its great as I can re read some discussions if needed.
Great work thanks again

[Oonrahnjay]

Probably golfcart, maybe L-16, perhaps something else if I can get a good deal on them.   I made two pull-out drawers that each have space for four batteries, but because I have two separate systems running in parallel I could conceivably have different types of batteries in each drawer, provided the controllers can handle them.   I'll be charging golfcart batteries at the upper end of their 5 to 13% recommended charge rate  -  my intention is to have the batteries fully charged by midday or very soon after, leaving all the panels' output during the afternoon for heating water or running power tools etc.

I had to use two controllers because I want to keep the house system the same 12V as the chassis, otherwise life gets too complicated with different voltages.   The theoretical disadvantages of 12V for heavier loads are offset by the simplicity of having everything able to run off any source, including connecting the house batteries to the chassis in emergencies.   Simple is good!

John

   Thanks, John.  Not AGM?  Won't they charge quicker (i.e. let you take advantage of the best sun time)?   

[bevans6]

It's less that AGM charge quicker than wet at the same charge rate, it's more that AGM can accept a higher charge rate so can be charged faster.  If the solar system can deliver say 25 amps at 14.5 volts charge rate you can charge a 250 AH bank at 10% for wet or AGM, but if you can get 75 amps at 14.5 volts you can charge a 250 AH AGM bank in a third the time.  Roughly speaking, of course.  Usually a solar system is charge rate limited by the output of the field.  The other big advantage of AGM deep cycle batteries is they can be discharged to around 20% SOC while wet batteries should only be discharged to 50% SOC before you start to hurt their life significantly.  Wet cell manufacturers actually recommend no more than 80% SOC for best life.  That means an AGM bank could have double to triple the usable capacity for the same AH rating.  It's all a balancing act.

Brian

[Oonrahnjay]

It's less that AGM charge quicker than wet at the same charge rate, it's more that AGM can accept a higher charge rate so can be charged faster.  If the solar system can deliver say 25 amps at 14.5 volts charge rate you can charge a 250 AH bank at 10% for wet or AGM, but if you can get 75 amps at 14.5 volts you can charge a 250 AH AGM bank in a third the time.  Roughly speaking, of course.  Usually a solar system is charge rate limited by the output of the field.  The other big advantage of AGM deep cycle batteries is they can be discharged to around 20% SOC while wet batteries should only be discharged to 50% SOC before you start to hurt their life significantly.  Wet cell manufacturers actually recommend no more than 80% SOC for best life.  That means an AGM bank could have double to triple the usable capacity for the same AH rating.  It's all a balancing act.

Brian 

     Yeah, that's pretty much what I was (clumsily) getting to.  But what happens if a solar array can put out 75 amps but the batteries will only accept 25?  Does the battery get cooked?  Does the "extra" charge just "not happen"?   If the charge controller holds the charge at a max of 25, doesn't that mean that you're losing a big chunk of your charge capacity during peak sun times?  After all, there's a curve to solar output; low in the AM, high at midday, and low in the late PM.  You wouldn't want to lose any opportunity to charge with all the panel output, right?

And balancing, yes, like $$$ balanced against no-$$$.   

[bevans6]

I think that's why you have a charge controller, so that batteries don't get cooked.  If your solar setup has excess capacity, it's just like it wasn't ever there.  It only counts if it gets used by something.

Brian

[Oonrahnjay]

I think that's why you have a charge controller, so that batteries don't get cooked.  If your solar setup has excess capacity, it's just like it wasn't ever there.  It only counts if it gets used by something.      Brian

    That's what I would have guessed (but if I don't know, I ask).  But my estimation was right ... if you have an hour of big sunshine and you don't put all that energy in a battery, it's lost?  Thanks, this solar stuff is all new to me ... and I never caught on to all those electrictron things anyway.

[bevans6]

It's like you have a 200 amp service at your house, but all the lights are off.  The 200 amps isn't getting used so it's just like it wasn't there.

Brian

[Iceni John]

Exactly.   I will have the potential ability to put up to 120A into my batteries, but most of the time they'll be charging at much less than that depending on their SOC.   When using solar the high-power appliance should be used after the batteries are on float, so load-management is the key.   Charging the batteries is always the priority.

John

[Lostranger]

I'm glad this thread took a turn toward solar. I got my grounding questions answered along the way, and now we get to talk about important alternative energy stuff. We're a year and a half off grid at the end of this month. Other bus nuts can do the same.

Jim

[Jim Eh.]

I was wondering if charging with solar while there is possibly significant draw on the batteries affects battery life? Does the inverter run off the batteries or more off the solar panels (almost directly)?

BTW, Kenworth, White, Frieghtliner all had positive ground (DC) systems "back in the day". I understood it had more to do with reducing body/chassis corrosion somehow.

[Iceni John]

I was wondering if charging with solar while there is possibly significant draw on the batteries affects battery life? Does the inverter run off the batteries or more off the solar panels (almost directly)?

The connections to the batteries from the panels' charge controller, and the connection from the batteries to the loads, are one and the same.   In effect the load is driven from the CC's output, but via the batteries.   I.e., if charging at 50A while drawing a 50A load, the batteries' net loss or gain is zero;  if charging at more than their load drawn out, the batteries will still be charging, albeit at a slow rate, and if the charging is less than their load the batteries will be slowly depleted.   Battery life is dependent on depth of discharge, number of cycles, plate sulfation, and to a lesser effect their rate of discharge (subject to Peukert Effect and all that good stuff).   However, battery life should be longer if charged by solar, for the simple reason that the batteries should get fully charged almost every day within a few hours, and they are constantly getting a top-up charge during the day.   For this reason I'm hoping that I can get a long life from cheap basic FLA batteries like golfcart or similar, but I plan on having a DOD of no more than 25 to 30%.   If I can get eight years of useful life from my batteries I'll be happy.

Maybe I should tell folk that my bus has radiated-thermonuclear charging powered by off-site fusion of helium atoms.   Yeah!

John

[bevans6]

"BTW, Kenworth, White, Frieghtliner all had positive ground (DC) systems "back in the day". I understood it had more to do with reducing body/chassis corrosion somehow."

This is pretty much correct but backwards.  There is always galvanic corrosion potential in an electrical connection with dissimilar metals.  Positive ground systems tend to save the copper wire and sacrifice the chassis.  Negative ground systems tend to save the chassis and sacrifice the wire.  I never really thought about it much, but telephone systems use negative 48V for the subscriber loop, that is positive ground to keep the copper wire from corroding.  In a vehicle it's easier to fix a wire than a chassis ground point.

Brian

[Oonrahnjay]

"BTW, Kenworth, White, Frieghtliner all had positive ground (DC) systems "back in the day". I understood it had more to do with reducing body/chassis corrosion somehow."

This is pretty much correct but backwards.  There is always galvanic corrosion potential in an electrical connection with dissimilar metals.  Positive ground systems tend to save the copper wire and sacrifice the chassis.  Negative ground systems tend to save the chassis and sacrifice the wire.  I never really thought about it much, but telephone systems use negative 48V for the subscriber loop, that is positive ground to keep the copper wire from corroding.  In a vehicle it's easier to fix a wire than a chassis ground point.

Brian 

     Lucas used that similar logic decades ago.  My '62 MGA had pos ground but by the time I went to work for Norton motorcycles in 1972, we'd gone to neg ground (and Lucas was supplying all their new-OEM components in neg ground).

[Jim Eh.]

Maybe I should tell folk that my bus has radiated-thermonuclear charging powered by off-site fusion of helium atoms.   Yeah!

John

   

Haha. Just don't tell your insurance agent!

Reason I was asking is there is a difference for us in the shop when testing, say an ABS system using a battery vs a battery charger. Using a small 10A battery charger will not power the ABS system properly and we have to use a charged battery(don't know why). I was just wondering if it would make any different to special electronic devices or systems using solar but I assume the controller would take care of that?

[Jim Eh.]

"BTW, Kenworth, White, Frieghtliner all had positive ground (DC) systems "back in the day". I understood it had more to do with reducing body/chassis corrosion somehow."

This is pretty much correct but backwards. 

Brian

Yeah, seemed that way to me!