New member / New build coming up!

[KS_Kampers]

Hello all. Found this forum after stumbling on Will's youtube channel. Currently planning a DC system upgrade for my new-to-me Grand Design 268BH and thought I would start to talk out a plan.

My new 5th wheel has the horrendous Schwintek slide controller on it, and DC voltage brown out is not tolerated. We boondock exclusively for up to 2 weeks at a time.

Our previous trailer was a bit smaller in terms of electrical load, and we used two golf cart acid batteries, a SunSaver MPPT, and a 200W panel. This worked surprisingly well for us, in spite of (or perhaps due to?) its simplicity.

I'm sort of SWAG'ing my anticipated needs, and upsizing a bit for margin. I'm moving to LiPO for the first time, and have zero experience with that. I do have a EE background and used to support BMS systems for satellites, so I'm not a complete noob. BUT this was years ago, and I don't have a feel for the BMS stuff in today's consumer level batteries.

We won't be using any inverters in our application. Only DC for lights, water pump, heater, fridge condenser fan, bath fans, USB stuff, and the evil Schwintek slide system.

Based purely on empirical and gut feel guidance (power use survey impossible to do without actual use of the camper), I am going to proceed with the following. My plan is to install the batteries / shunt / MPPT controller behind the false wall in the pass through, and bring a power cable to the front factory installed bus bar.

Li Time 100aH trolling motor batteries x 3
Charge status shunt monitor w/ bluetooth connectivity (vendor TBD)
50-ish Amp MPPT solar charger (vendor TBD)
200W solar suitcase panels x2 (vendor TBD)
And of course a laundry list of disconnects / breaker / bus bar / etc.

I'm browsing this site like crazy. I will undoubtedly have lots of LiPO questions.

Nice to meet you.

Frank

PS... see the TBD stuff above? feel free to send suggestions. Money IS an object.

 

[wdwtx2.0]

Welcome aboard.
This forum is a treasure trove of information.
There are some really experienced people here who can help you with about any question you may come up with.

 

[Solarcabin Channel]

First thing I would do is check the specs on the RV converter and see what it is compatible with.

 

[MisterSandals]

I'm moving to LiPO for the first time,

LiPo is lithium polymer, the explody kind of lithium battery. Be careful what you order!

Hopefully you mean LiFePO4 (lithium iron phosphate). AKA "LFP"

 

[wme]

Is there an inverter in your future? For pure DC loads your over batteried, "think" about roof mounted 200w solar (their dirt cheap). One deployable panel is nice if your parking in the shade.

 

[KS_Kampers]

LiPo is lithium polymer, the explody kind of lithium battery. Be careful what you order!

Hopefully you mean LiFePO4 (lithium iron phosphate). AKA "LFP"

Yup. I was being lazy

 

[Hedges]

Start with peak & surge current draw of loads.

One big battery preferable to multiple smaller BMS, if you need more current than one can deliver.

 

[KS_Kampers]

First thing I would do is check the specs on the RV converter and see what it is compatible with.

Yup. This. Hoping that my RV converter supports "LFP" batteries. Otherwise, throw a Progressive Dynamics converter into the fray.

 

[Solarcabin Channel]

Yup. This. Hoping that my RV converter supports "LFP" batteries. Otherwise, throw a Progressive Dynamics converter into the fray.

You can get converters for the higher volt an LFP takes on Amazon. I looked one up for someone a few days ago.

 

[KS_Kampers]

I've got a WFCO WF-9855 (NOT the AD model that auto detects. Thanks, Grand Design!)

Oddly my buddy has this same model, and it keeps his 4x 100Ah SOC LFPs fully charged on shore power. I note that this converter does bulk charging at 14.4V, so maybe (?) its on the hairy edge of being adequate.

I still think I will swap mine out. Sadly though... the wiring behind my panel to get to my converter is a spaghetti bowl. I'm not sure I'll be able to easily access. It will require some cirque du soleil physical manipulations.

I sort of wish I had not opened this up. My respect for the build quality of this camper went way down.

 

[Rednecktek]

If you do feel up to rolling your own, you can fit a 12v 304ah battery with 200a BMSin the same space as a Group 31 battery. That would be the same capacity with about 1/3 the physical footprint and accociated wiring.

 

[MisterSandals]

I note that this converter does bulk charging at 14.4V, so maybe (?) its on the hairy edge of being adequate.

Are you thinking 14.4V isn't high enough?

I purposely didn't buy the PD lithium aware inverter/charger because i don't want to charge that high (and i believe it floats there too). My top charge voltage is 13.8V which i consider i gentle 99% charge.

Are you expecting your 3x LiTime batteries to be balanced enough to charge to 3.6Vpc everyday without any cell over volt on the BMSs?

 

[KS_Kampers]

Are you thinking 14.4V isn't high enough?

I purposely didn't buy the PD lithium aware inverter/charger because i don't want to charge that high (and i believe it floats there too). My top charge voltage is 13.8V which i consider i gentle 99% charge.

Are you expecting your 3x LiTime batteries to be balanced enough to charge to 3.6Vpc everyday without any cell over volt on the BMSs?

Heck... I don't know enough yet to comment on how these BMS batteries work (side note : I used to field-support satellite power management systems including the first BMS products for space stuff. I don't expect bulk consumer Chinese products to be very similar in quality).

I try to not expect anything that isn't supported in writing.

I'm thinking that 14.4 is an absolute number, and I know that margins and tolerances should be always spec'd by reputable vendors. For a converter not designed for Li batts, I don't know how a "smart" converter designed for Pb will interface to it in terms of outputting bulk / float / absorption modes when attached to Li. The Li Time Batteries show a charging voltage of 14.4 +/- 0.2V. I hate doing so, but I gotta speculate that is the operational range. No absolute max, no absolute min, no voltage input derating performance sort of stuff. Grrrrr..........

What I expect is for the vendor to provide me the requirements for their product, and I will design the rest of the system to satisfy the needs of that product in order to fulfill the obligations of their warranty policy

 

[MisterSandals]

The Li Time Batteries show a charging voltage of 14.4 +/- 0.2V. I hate doing so, but I gotta speculate that is the operational range.

I agree that that is within the safe operational range for the battery as a whole.

My understanding, based on what i have seen here and what others have experienced, is that its the cell level voltage differences at the extremes (under 3.0V, over 3.6V) make it less likely to be able to charge to 14.4V without the BMS cutting out.

Its great that the BMS saves the battery, but frequent or daily trips greatly shortens the longevity of mossfet based BMS in particular. I believe that having a cell(s) hitting the safe limits regularly shortens their life too. Its like revving your car to the redline at every shift; its within the manufacturers safe zone but there is definitely more stress on the system and i equate that to less reliability and longevity.

The reality is that LFP usefully charged far below 14V and the additional battery capacity difference between 3.45V and 3.6V is less than 1%.

Back to cell imbalance issues, when folks have them, the solution to living with their battery reality of charging to a lower (pre over volt disconnect), its VERY desirable to have a configurable charge profile (can be set to charge lower).

Thats the trick, cell voltages, not battery voltage. Unfortunately people don't understand the importance of this distinction until they have a system that does not work and cannot simply be adjusted.

 

[KS_Kampers]

Thats the trick, cell voltages, not battery voltage. Unfortunately people don't understand the importance of this distinction until they have a system that does not work and cannot simply be adjusted.

Interesting! That would definitely be a big difference between the higher end batteries and the lower. From what I can tell, the Li Time trolling batts have zero ability to access the BMS data. My hunch is that I will probably only put 20-30 use cycles on my batteries annually, and after picking a bunch of brains I have downsized my array to a grand total of 2 batteries. Perhaps my next set will be better featured.