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Motorhome Build Thread
#1
Hello all, ok, so I've been hovering and absorbing info at all levels before I go build/ lash out thousands on a perfect setup. Here lies the problem, I've been an electrician for almost 40 years now, very capable with the building/wiring aspect BUT have tied myself up in knots with the design aspect. I shy away from the maths calculations naturally involved with design as one would. I want to put down here my concerns and hopefully someone chime in here and put me straight. I thought I had a system truly sorted in my head but oh NO...!!!

Parameters......
1. 24v battery bank running system to match the truck starter system. 
2. Space for 6 solar panels up top. I will fabricate a mechanism to tilt them L to R for maximum efficiency.
3. Allowance for 3kw of 240v inverted usage. 
4. Battery choice...???? I want to run 2 x LiFePO4 200ah batteries in series.
5. Main aim to be 'OffGrid' sufficient. 

Q's :  
1. Solar panels in series or parallel for use with an inverter..?? Main 240v usage will be the AC unit @1200watts and a washing machine intermittently used @ 2000/3000watts (diversity applied in conjunction with AC unit).
2. Battery choice, do LiFePO4 batteries like to be maintained at all times hooked up to a solar system charger or do they like to 'cycle'..??? Would I be better to use AGM batteries...???? I agonise over this choice switching constantly from one to another, maybe I'm missing a few good and obvious pointers here to help me...???
3. Absolute protection for battery life, charger choice etc..?? I DO NOT want to kill a very expensive battery bank with a novice build mistake...!!!

If anyone can do me a layout drawing of your suggested idea that would be great. I've plucked several from Google image but am hesitant to take on the construction until I've tapped into and sought advice from a 'think bank' such as here...

Thanks in advance,  Mez
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#2
(09-29-2020, 04:37 AM)Mezbatt Wrote: I will fabricate a mechanism to tilt them L to R for maximum efficiency.
Be sure to build for the flexing & vibration of road travel... if going ahead with this, a simple manual method might be good?

(09-29-2020, 04:37 AM)Mezbatt Wrote: Q's :  
1. Solar panels in series or parallel for use with an inverter..?? Main 240v usage will be the AC unit @1200watts and a washing machine intermittently used @ 2000/3000watts (diversity applied in conjunction with AC unit).
The panels & the inverter aren't really related.... other than the charger you use. Look for an MPPT charger that will take the voltage & current of the panels up to Voc (STC) & Isc (STC)
"STC" is one of the panel specs. You will actually get output more like the NOCT numbers but you should spec it for the STC ones.
Typically the optimum voltage for the panels is with the panels at Vmp (NOCT) about 10V higher that the battery bank "full" voltage.
You might wire two panels in parallel to one smaller MPPT & the other two to another MPPT. This gives you a bit of redundancy & some shade handling.

(09-29-2020, 04:37 AM)Mezbatt Wrote: 2. Battery choice, do LiFePO4 batteries like to be maintained at all times hooked up to a solar system charger or do they like to 'cycle'..??? Would I be better to use AGM batteries...???? I agonise over this choice switching constantly from one to another, maybe I'm missing a few good and obvious pointers here to help me...???
LiFePo4 cells are more expensive but are lighter & smaller than SLA/AGM batteries & will last way longer if charged properly.
If you charge the LiFePo4 cells to approx 3.40V - 3.45V/cell they are are happy to sit there all day & not "need" cycling.
They are also not damaged if left at lower SoC like SLA/AGM's are.  80% DoD is OK, <50% is better (any DoD takes some cycle life off any battery type).
Do not charge them to 3.65V/cell, also don't go below about 2.9V/cell, they won't last. Stay on the "flat part" of the voltage curve.
You could also buy individual cells instead of pre-built 12V blocks, you get better access to each cell if you do.

(09-29-2020, 04:37 AM)Mezbatt Wrote: 3. Absolute protection for battery life, charger choice etc..?? I DO NOT want to kill a very expensive battery bank with a novice build mistake...!!!
Use a good BMS - Batrium is the best but you can probably pick a lesser one. You need an alarm output for cell high/cell low.
Use a good battery monitor like a Victron BMV-712 - tells you SoC, volts, current, etc
Use good chargers like a Victron MPPT
I've got Victron gear myself & love it.
Use proper non-polarized DC breakers like No-Arc for smaller loads & a big one for the inverter.
Use pre-charge methods.

(09-29-2020, 04:37 AM)Mezbatt Wrote: If anyone can do me a layout drawing of your suggested idea that would be great. I've plucked several from Google image but am hesitant to take on the construction until I've tapped into and sought advice from a 'think bank' such as here...

Thanks in advance,  Mez
As long as you build it modular, you can change, add, repair, etc much more easily.
Run as much as possible (eg lights, etc, etc) directly from DC, or via DC-DC 24v > 12V converters, much more efficient.
Laptops, phones, etc can all be run this way.

Look for electronically controlled appliances, & lower wattage eg washing machine, microwave oven, etc will draw less current.

Post some links to diagrams you like & we can comment on them! :-)
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Running off solar, DIY & electronics fan :-)
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#3
This might be interesting for you. The guys doing the "Long Way Up" adventure show/documentary built a tilting+sliding tray design to fit 6 large PV panels onto a Mercedes-Benz Sprinter van.

https://secondlifestorage.com/showthread...0#pid67950
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Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#4
(09-29-2020, 01:23 PM)Redpacket Wrote: "You might wire two panels in parallel to one smaller MPPT & the other two to another MPPT. This gives you a bit of redundancy & some shade handling"
Can you expand on redundancy and shade handling please..????


"Do not charge them to 3.65V/cell, also don't go below about 2.9V/cell, they won't last. Stay on the "flat part" of the voltage curve.
You could also buy individual cells instead of pre-built 12V blocks, you get better access to each cell if you do"

I thought about building a bank up but would it be as robust and fit for purpose in a truck (Race truck Volvo FL6)..???

This is where i get lost a little, do I buy individual MPPT controllers and an inverter or get a combined unit as per the Victron..?? My truck will do quite a bit of 'offgrid' if not mostly should the system prove good. I have to get this right. I have an onboard generator which may also be figured in SO:
1. Solar. 2. Battery bank. 3. 240v hook up. 4. 240v generator supply. ....????? 

(09-29-2020, 04:37 AM)Mezbatt Wrote: 3. Absolute protection for battery life, charger choice etc..?? I DO NOT want to kill a very expensive battery bank with a novice build mistake...!!!
Use a good BMS - Batrium is the best but you can probably pick a lesser one. You need an alarm output for cell high/cell low.
Use a good battery monitor like a Victron BMV-712 - tells you SoC, volts, current, etc
Use good chargers like a Victron MPPT
I've got Victron gear myself & love it.
Use proper non-polarized DC breakers like No-Arc for smaller loads & a big one for the inverter.
Use pre-charge methods.



I've fitted several shunt type monitors like the BMV-712 to systems when i worked on superyachts many moons ago so that will get figured in and a good prompt..... Also everything fitted was indeed Victron...!!!

Have a look at these batts that i have attached. Two of these in series and a good set up which I'm trying to config........

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#5
That Volvo FL6 looks like quite a large vehicle so should be able to do plenty of things.
Yes I'd suggest getting separate individual modules eg MPPT's, BMV-712, inverter.
You would be able to integrate a generator with switch over, etc.

Re shade, etc, if you cable all the panels in one lot to one controller, you may not get as much power collected.
So you put say 3 panels into 1x MPPT unit & the other 3 into another MPPT.
This way if some panels are shaded, you should get better results.
Also for redundancy, if eg a panel got damaged or one MPPT failed, you would still get some power input.

Cells like these would be good:
https://www.ebay.co.uk/itm/8-x-LiFePO4-3...3680672776

Maybe find a diagram you liked & link it here.
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#6
Parameters......
1. 24v battery bank running system to match the truck starter system.
There's no real benefit for matching since you would never power off the truck's SLA batteries. It's possible to charge the batteries off the truck, but you'll have to make sure you have a beefed up alternator and a separate charge controller to maintain the current.

2. Space for 6 solar panels up top. I will fabricate a mechanism to tilt them L to R for maximum efficiency.
Good idea. Go for mono panels as well for maximum efficiency.

3. Allowance for 3kw of 240v inverted usage.
Assuming you're not in the US otherwise you'd choose 120v? My take is to go with Victron stuff. Good efficiency and decent units. However if you are on a budget there's other stuff around.

4. Battery choice...???? I want to run 2 x LiFePO4 200ah batteries in series.
Not sure your budget but we have quite a variety of builds here from all sorts of different battery sources.  Not sure what 200ah LiFePO4 batteries are since that's just current. You might want to specify the voltage as well so we can calculate the kwh.

5. Main aim to be 'OffGrid' sufficient.

Q's :  
1. Solar panels in series or parallel for use with an inverter..?? Main 240v usage will be the AC unit @1200watts and a washing machine intermittently used @ 2000/3000watts (diversity applied in conjunction with AC unit).
Solar panels are rated based on the MPPT controller and the battery voltage. Typically you want to size the panels close to the MPPT zone for best efficiency. For example if you use 2 panels in series to get let's say 90V (Vmp) but you have 24V batteries, it's probably better to wire panels in parallel to get 45V (Vmp).
I would choose an AC unit that has an inverter (basically a variable speed compressor) as it will be less stress on your inverter. That way there's no hard starts or surge. Plus a lot more efficient so save more power. I've seen folks on tiny homes put actual home type mini-splits on their camper.

2. Battery choice, do LiFePO4 batteries like to be maintained at all times hooked up to a solar system charger or do they like to 'cycle'..??? Would I be better to use AGM batteries...???? I agonise over this choice switching constantly from one to another, maybe I'm missing a few good and obvious pointers here to help me...???
There's not much maintenance to the batteries if properly matched (we deal with a lot of used cells here in this forum so mismatched cells are a common theme here). Lithium cells are not like SLA/AGM batteries. They do not suffer any memory effects like nicads either. However the lifepsan suffers if cycled 100% daily. That's why a tesla car only charges up to 80%. At 100% depth of discharge every day they will run between 500-1000 cycles. If you reduce that to 70-80% you might increase your cycles up to 2000. A deep cycle SLA has probably 500-1000 cycles as long as you only do a 50% depth of discharge. So typically you need 2-3 times more 'capacity rating' for SLA than you need for Lithium. That means 4 times the size with 1/2 the capacity and 1/2 the life. So no SLA! Just don't do it! We won't like you and you wont' be welcome here!

3. Absolute protection for battery life, charger choice etc..?? I DO NOT want to kill a very expensive battery bank with a novice build mistake...!!!
That's what a Battery Management System (BMS) is for. But really if done right there's nothing to worry. The inverter you use would cut off before your batteries would wear out, and if not then your BMS would be your failsafe and have a secondary trip to cut off the voltage. If you however bypass this BMS by let's say powering up some 24v lights directly connected to the batteries, then all bets are off.
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#7
Thanks guys,

Starting to gain some momentum now, all posts greatly appreciated and read several times to absorb....

Reading reviews on equipment is proving a plus. Found a guy called Will Prouse on Youtube who's enthusiasm for LiFePo4 cells is very infectious indeed and the use of BMS. I'm now looking at cells from Ali Express as below, great reviews and delivery times etc....

It won't be for several weeks or even a couple of months until i take the plunge and purchase, I have a healthy budget but do not want to squander funds on unnecessary equipment either.   

This is a great forum and some good advice coming my way, thank you..!!

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#8
Will Prowse's videos are great & give good information. +1 for them :-)

200ahrs at assumed 24V system volts is actually a measure of storage capacity (a quite reasonable amount) & should run a van like yours well.
Your main power usage over time is likely to be a fridge so dig hard to get the most efficient & best insulated one there. Avoid small "bar" fridges like the plague!
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#9
Quick question : The panels I'm getting give out approx 37.5v & 230w. For a 24v battery bank is that sufficiant or should I link them in series/pairs to give 75v and run 8 panels through 2 MPPT controllers..??? 

Also this Victron unit : https://www.onboardenergydirect.co.uk/sh...tml#SID=37

   Sorry for this rudimentary picture but just look at the panel layout please..????
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#10
Solar side 37.5v for 24V system sounds a bit too low. Have to take into account that the panel voltage drops with temperature, and a 24V system actually has a full charge voltage of closer to 28V. And many solar chargers need a bit more voltage difference to operate efficiently and at full power.

Which panels specifically are you thinking of using?
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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