Just can't wrap my head around how to handle the battery bank...

[bobblefrog]

Hi all - 

I've been researching solar for awhile now, but I feel like I'm missing something basic because I can't figure out how to deal with the battery bank.  Currently I have one house battery housed way up in the engine compartment (21 foot class c on a truck chassis - not a van - I'd say a good 4 feet between battery and dashboard).  The converter and the breaker box are under and by the dinette midway.  

Currently the draw on the house battery is pretty small - led lights, one fan and the water pump (maybe the water heater has electric ignition - yet to test that system yet).  I'm going to be adding two vent fans to the system (rigging some 10 inch 12v to insert) and probably a 12v accessory outlet to charge cell phones. 

The only place for me to put additional batteries is to turn the dinette into a u-shape which should create just enough room for two 100ah AGM batteries (I can probably rig for 3 with care).  My hope is paired with three 100 watt mono solar panels/mppt I could then have enough to power laptops, jetpack, antenna, 1000w ps inverter and a 3.2 cubic foot compressor fridge (let's say 40 ah a day sans the inverter draw).

For that I was going to go mono flexies - put out when boondocking or have a place I can velcro them to roof if I'm in a place I don't feel comfortable putting them out ie a parking lot.  I can hang them in the bathroom while traveling.  All that seems to make sense, I can wire the fridge under the flooring and through the dinette to the system inverter.  Battery and controller and inverter all near each other at the dinette.

Then I figured I'd get another panel for the existing house - maybe a solar suitcase because then I wouldn't have to figure out where to put the controller - just alligator clip it in.  So then I'd have two systems.

This feels however like I'm overthinking it and maybe there's a simpler solution to combine everything - but I really have no idea how to wire these two locations together, or how to get the new solar system to wire into the main electrical system that already exists, or to get the converter to charge the new batteries when driving (have it split between the two locations).  It's like while I've figured out most of it-I'm missing some basics!

If anyone has any recommendations or thoughts - I'd appreciate them!!  I gotta get off the hamster wheel in my brain!

 

[BradKW]

For starters, the first question I have is what is the existing House battery, and what is that space's dimensions? Thought being that you might be able to replace it with a big 8D AGM or something for a big improvement...but need to know what you're currently working with.

Also consider an underbody mounted battery box...I'm sure there's room somewhere.

I have two solar systems in my truck, a 12v and a 24v and it adds to the complexity only a little bit, but I would probably suggest going with a single battery bank in your situation

 

[SternWake]

Engine heat is not really good for batteries.

Despite the millions of batteries under the hood, these batteries are not deeply discharged/ deeply cycled regularly, and when only slightly discharged, they cannot accept much amperage and as such do not heat up from within, only from ambient engine bayt temperatures

When a battery is depleted, and can accept higher amperages, they heat up much more. Combine this with engine heat and it is a bit more detremental to them.


I'd go for a new house bank in the back to keep wiring runs from solar panel/ controller to battery shorter

 

[bobblefrog]

For starters, the first question I have is what is the existing House battery, and what is that space's dimensions? Thought being that you might be able to replace it with a big 8D AGM or something for a big improvement...but need to know what you're currently working with.

Also consider an underbody mounted battery box...I'm sure there's room somewhere.

I have two solar systems in my truck, a 12v and a 24v and it adds to the complexity only a little bit, but I would probably suggest going with a single battery bank in your situation

Yeah, just a typical marine deep cycle in the opposite corner from the starting battery, and not really even well mounted - just two long bolts holding in the plate it sits on.  There might be some room in there to come up with a larger mounting system.  Although, considering that and per the comment below, it does seem like it may make sense to consolidate everything in the new area.  

There might be a place to put it under - hmm.  Actually hadn't thought about that or looked.  So far every square inch of the camper is utilized but it does ride somewhat high so there might be some place under the chassis to tuck a battery box.  

Thanks!  I'll do some more poking.

 

[Optimistic Paranoid]

Just remember, unless it's a sealed battery, like an AGM, you'll need regular access to it to add water.

 

[TucsonAZ]

Not the ideal system and sounds like the makings for endlessly undercharged batteries. I only really do 24v systems myself but was in a motorhome this past year where I enlarged the battery try and put two 100ah AGMs, first thing I did was to add a PowerMax converter as I find that a mandatory upgrade no matter what. If I'd added solar I would have just hooked that up to the bank but I was fine with just the generator running here and there and shore power. All the same, I would at the very least get an EPsolar charge controller and a 300 watt grid tie panel attached to the roof if you want to add a second bank. Tying them in together wouldn't be wise, I would let the coach battery just do it's own thing and the other bank for the higher power draws. Or move all batteries up front and accept that the heat won't be great for them.

 

[bobblefrog]

Not the ideal system and sounds like the makings for endlessly undercharged batteries.  I only really do 24v systems myself but was in a motorhome this past year where I enlarged the battery try and put two 100ah AGMs, first thing I did was to add a PowerMax converter as I find that a mandatory upgrade no matter what.  If I'd added solar I would have just hooked that up to the bank but I was fine with just the generator running here and there and shore power.  All the same, I would at the very least get an EPsolar charge controller and a 300 watt grid tie panel attached to the roof if you want to add a second bank.  Tying them in together wouldn't be wise, I would let the coach battery just do it's own thing and the other bank for the higher power draws.  Or move all batteries up front and accept that the heat won't be great for them.

I really appreciate the thoughts.  Yeah.  I have to update the converter.  It's on the list.  Assume PowerMax is what they call a 3 stage?  On the east coast I'll almost always be hooked up for shore power - but I want the capability for boondocking out west three-four months out of the year and will have to be able to work remotely.  The fridge isn't essential then (nondairy creamer ain't my favorite but it won't kill me). But my internet and ability to keep my equipment up and running is.  I was also going to get a small portable generator - there is just one small bay for an original generator but I've already got it planned for toolbox, plumbing etc.  If I had the money I'd replace the bumper toolbox with a cargo carrier (currently it's just heavy and small) but don't think that's going to happen. Just going to have to figure out what I can sacrifice (ie the BF doesn't have to come...!) when I do so I can go lean.

If I do stay with two bats up front in the engine - where would you put the controller?  Is it okay say15 feet away?  What gauge cable am I looking at if I need to do that?  It's opposite side battery bank and through the engine, the cab and to the center of dinette will be that far.

 

[AuricTech]

All else being equal, I'd rather have the charge controller closer to the battery bank than 15', to minimize voltage drop.  However, you know the layout of your rig, and I don't.

As for wire gauge, my sig file includes a link to an online voltage drop calculator.  Play around with distances and wire gauges, and see what works for you and your rig.

ETA: If you go with the combo of a "grid-tie" panel and MPPT controller, as suggested above, voltage drop between panel and controller will be less of an issue than it would be with "12V" panels.  Voltage drop issues between the controller and battery bank will remain the same.

 

[bobblefrog]

All else being equal, I'd rather have the charge controller closer to the battery bank than 15', to minimize voltage drop.  However, you know the layout of your rig, and I don't.

As for wire gauge, my sig file includes a link to an online voltage drop calculator.  Play around with distances and wire gauges, and see what works for you and your rig.

ETA: If you go with the combo of a "grid-tie" panel and MPPT controller, as suggested above, voltage drop between panel and controller will be less of an issue than it would be with "12V" panels.  Voltage drop issues between the controller and battery bank will remain the same.

That calculator is a great resource!  Two questions about that - what qualifies as a connector?  Single set would be terminal at either end?  What if you have an inline fuse?  I found I can get it right at 3% for 15 feet with 6 gauge copper wire, single set of connectors 30 amp (which of course it would not be that much - that's the most my system could handle).  So I know that's "safe" but with some thought into load I could consider 7, etc.  Just keep playing with numbers.

 

[SternWake]

4 gauge wire is thicker than 6 gauge wire. The bigger the number the smaller the diameter of the wire, until you get thicker than 0 gauge, then it goes 00 000 and 0000 for 4 ought or 4/0, depending on who is speaking/typing.

If you might add more solar in the future, then oversize the wire run from panel to controller now, as it will be cheaper and easier than running additional or thicker wire later.

As far as replacement converters go, I think the Progressive dynamics 92XX series of converters as pretty good, as one can force the unit to one of 3 voltages, and they offer a unit with a 14.8 volt absorption voltage, which will recharge faster and more completely. The XX is the max amperage of the specific model. they go upto 80 amps, but these require a 20 amp receptacle. The 70 amp model works on a 15.

If plugging into the grid time to recharge fully is much less of a concern compared to running a generator to recharge. If running a generator then getting the batteries to and holding the batteries at absorption voltage is paramount for fastest possible charging, and the PD converters can accommodate this goal.

Iota will hold 14.8 for 15 minutes before reverting to 14.2v, which slows charging
Powermax 3 or 4 stage tend to drop to 13.8v as Soon as it first reaches 14.4v on the converter output terminals which slows charging to a bigger degree
The PD92XX series will seek at( or near) the maximum amperage rating, and hold 14.4v or 14.8v, for 4 hours, and can be forced to any of the 3 voltage 'stages' at any time via their remote/pendant/wizard.

Using these converters it is important to use thick short copper to battery terminals, so the converter output voltage is as close as possible to actual battery terminal voltage. Most will not accept thicker than 4awg wire.

Powermax offers an Adjustable voltage single stage manual converter/charger. It will seek and hold voltages upto ~15.5v, and hold that voltage until a human with a brain either unplugs it, turns the voltage down, or the generator runs out of fuel. So there is the risk of overcharge, but these are good for the human who does not require everything be automatic, and those recharging via generator, or those wanting to be able to perform an Equalization charge on their flooded batteries

Technically EQ voltages can be as high as 16.2v at 77F battery temperature, so 15.5v falls short of Trojan and Rolls surrette EQ voltage recommendations, but the EQ charging at these lesser voltages should just take longer before specific gravity maxes out on all the battery's cells, but some older abused batteries might not respond well to 15.5v but will to 16.2v, when an EQ charge is required.

I use a modified Meanwell power supply(rsp-500-15) to choose any target voltage I want, but the modifications for holding 40 amps all day long safely, and easily adjusting voltage are not child's play. the powermax adjustable voltage versions are much more user friendly, but there have been some issues with customer service, and some require a bit more voltage twiddling after 15 minutes at max voltage, unless there is a resistor leg snipped inside the unit.

I would order the adjustable voltage versions from Errin directly:
http://powermaxconverters.com/contact/

Here is a middleman's link for the manual single stage adjustable voltage versions:
http://www.bestconverter.com/Specialty-Converters_c_230.html

Note the powermax versions sold elsewhere are the automatic 3 or 4 stage versions, and these are not so great for generator charging, or charging to full in minimal time. Some will be 14.4v versions, other will be 14.6v depending on the seller/source.

 

[bobblefrog]

Again, realizing I missed that the thread continued and wanted to follow up and offer thanks for answers.

Made it to Quartzsite and have been finishing out my system with help from VanKitten, JiminDenver and another good friend I've met here who ensures I don't knock myself on my tush up when I start messing with wires. Ultimately utilized 6 gauge for everything (thanks Jim) with the exception of some 2 gauge I found tied up under the chassis (that had been left over from the generator that had been removed by the previous owner). Used that to run from the house battery in the engine to the solar controller that I installed in the dinette nearer the new/additional battery (although did have to strip it down to fit into the inline circuit breaker).

Everything else was in the dinette cabinet, including ground, and 12v sockets (thanks Kat) so I'm well covered.

Learned a lot about wire! Including that I need better wire cutters and I envy Jim's hydraulic crimpers Also, that in addition to stripping down stranded wire that is too big, that wire that is thinner than a terminal connector end can be doubled over to fit better. For example, if the auto parts had connectors that would fit the battery post but the other end was for 4 gauge and not 6...

I ended up letting the RV fixit place recommend the new converter (but we are thinking that was in error - that if the original converter was converting, and not charging the house in the engine when hooked up that something was simply not hooked up). In addition they piggy backed it, instead of fully installing it, but not sure how it's working exactly and we're still going to futz around and finish that job correctly and hopefully connect that into my new battery as well. The new converter seems solid enough - Power Dynamics Intelli-Max 9100.

 

[bobblefrog]

Oh yes, and should clarify - we did end up keeping my banks separate.

So - original house battery in engine compartment of truck (so starting battery is on one side, house on the other). It is easy to hook to my 100 watt portable suitcase. But it is now also connected to controller under the dinette (Morning Star Duo) so the 200 watts on the roof can give it a little charge too. That duo allows a 50/50 split between banks or 90/10. That battery now pretty much covers my lights (all led), water pump and furnace.

The new 100ah agm sealed is under the dinette (which had some venting into the cable bay) and it is hooked into the other side of the duo. It feeds through a bus bar currently to a 3 socket 12v panel wired in parallel that gives me a charging bay under the table for my 12v devices and an inverter that I use to charge my camera batteries, a lamp with led lights and my macbook.

For my situation I'm super happy with the split banks.