#153017  by NeilV
 Sat Jul 13, 2019 8:54 pm
Hi all,
So I’m taking the plunge into the lithium, and been trying to find all the ‘cons’ in switching my newish AGM system over (while living in it fulltime on the road with my family of 4 this year ;) )

Firstly, those with the ‘standard’ Waveinverter (Nomad) 300W+Samsung fridge combo... does this inverter play nicely with the much higher voltage of Lithium?
The manual I googled for says “voltages over 1.5 times rated will damage” it, but doesn’t say what it’s “over volt/undervolt” protection settings are?
Will it warn/cut out before the 22v I’m informed my lowest cutoff should be?
 #153023  by scubadoo
 Sat Jul 13, 2019 10:20 pm
Neil

The slightly higher and stable voltages delivered to your inverter will provide more benefits than disadvantages. Marginally higher efficiency and lower current come to mind.

Worst case my 4 cell battery pack will disconnect at 12.1V hopefully long before the 300W inverter ever decides to stall from low voltage.
At 12.1V and with typical current draw my pack would have no more than perhaps a few percent SOC remaining.
It has yet to drop below 12.85V in 4 plus years of fulltime travel.
11V or 22V to the inverter in your proposed setup should never occur. The battery pack would be exhausted and facing (theoretical) doom.
 #153025  by NeilV
 Sat Jul 13, 2019 11:23 pm
scubadoo wrote:
Sat Jul 13, 2019 10:20 pm

Worst case my 4 cell battery pack will disconnect at 12.1V hopefully long before the 300W inverter ever decides to stall from low voltage.
At 12.1V and with typical current draw my pack would have no more than perhaps a few percent SOC remaining.
It has yet to drop below 12.85V in 4 plus years of fulltime travel.
11V or 22V to the inverter in your proposed setup should never occur. The battery pack would be exhausted and facing (theoretical) doom.
The 22v is based on a comment from Chris (Nut17) who said that should represent 15% SoC on the batteries he’s selling me? They are the older 3.2v/cell ones, so maybe the calculation is different?
Also,what do you use to prevent them going too low?

Another thing is the charge voltage from my solar... I see max voltage from the panels (in parallel) as 30.5, and the charge current for the cells I’m buying is 3.65ea=29.2v and cut off at 3.85v=30.8v.
Should I think about making them series to reach a high enough voltage for the MPPT to use effectively?
 #153035  by scubadoo
 Sun Jul 14, 2019 9:24 am
Neil I can only comment on my Sinopoly battery pack.
22V is 2.75V per cell if they are perfectly balanced. There would be some remaining capacity not much at all and just a little too close to 0V for my liking especially if you are not there to react.
During my occasional 30A discharge capacity measurements I terminated the test when the first cell reached 2.80V. At that point all tests to date have exceeded the rated 300Ah capacity. From memory without looking up my data the time for the battery pack to drop from my emergency 12.1V cut off point and shutdown at 11.2V - 22.4V equivalent for your setup was less than 5 minutes.

I use one of these: Victron BatteryProtect 12/24V BP-100 There are also 60A? and 220A versions available. The shutdown voltage can be set lower if necessary and the 16V shutdown at the high end is an added bonus if everything else in my setup fails.
There are many other methods and I originally used my own design with a combination of aliexpress components and solid state relays. I somehow sleep easier leaving it all to the purpose built Victron device. :TU

I doubt your inverter will ever see or alarm with high/low voltage levels. Mine has not.
 #153051  by NeilV
 Sun Jul 14, 2019 8:36 pm
Will this do it?

So much cheaper from Amazon!
https://www.amazon.com/Victron-BPR00010 ... 01N6ATT8C/
 #153053  by scubadoo
 Sun Jul 14, 2019 9:13 pm
That is the smaller unit of my 100A model. As long as you have no plans to exceed 65A in total for all the output loads it will do the job.
I am happy with the device although it has never triggered except to test operation. ;)

Here is the operation manual to read prior to any purchase decision.
https://www.emarineinc.com/Shared/pdf/V ... Manual.pdf
 #153171  by NeilV
 Fri Jul 19, 2019 9:09 am
Luckily 65 A on my 24v (1440W) is equal to 130A on your 12v :TU

The 65A one will match my Daly BMS 60A load limit quite nicely... especially as the BMS is on the negative, and the BPM on the positive... if I want to squeeze the full 65A out I can put the inverter negative on the BMS and positive on the BPM ;)

Looks perfect if I set it to ‘option 8’ and use it as a 24v bottom cutoff, and will even run my 1,200 inverter happily too (as long as I don’t use a ‘motor’ bigger than 700W with a ‘ramp up’ load higher than 1400W).
 #153298  by NeilV
 Wed Jul 24, 2019 9:38 pm
So my brain has been freewheeling for a while on LifePo4 stuff, and my current “brain fart” is to connect the 300W fridge inverter (and my main load by a HUGE margin at a minuscule 12.5A max @24v) to the 40A rated output of my Tracer 4210AN solar controller.

Since my Lithium’s will be Voltage rated, it doesn’t really matter as much to have accurate SOH reading from the ‘very cheap battery monitor’, but could be a great way to drop the fridge load at 30% SOH for LifePo4 (26v on my 24v system [or 13v@12v] as this would also trigger the inverter alarm which auto cancels as it drains its capacitors (inevitably at 2am!)

Another bonus might be to have the fridge cycle off say 5 hours after sunset, and minimise the overall load too?

While awaiting my lithium delivery, I’ve been using the house AGMs to crank the engine too, so I’ve been turning the fridge off overnights anyway? (after the starters were killed a few weeks ago)

Any reason this is not a good idea?
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