Caravan off grid set up.

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Re: Caravan off grid set up.

Postby Gordon-Loomberah » Sat Oct 27, 2018 12:56 pm

davidg wrote: For LiFePO4 it would be whatever the manufacturer might state as the maximum.


...but in practice for normal DOD<50%, it will be limited by whatever that battery can accept at Vabsorb, and at least in the case of CALB, nowhere near 1C.
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Re: Caravan off grid set up.

Postby Al510 » Sat Oct 27, 2018 1:36 pm

With the 2kw available at peak it would be under 0.2c so should be no problem with the CALB cells?
Also Gordon, do you have any suggestions regarding the smaller cells vs larger, or CALB vs Winston?
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Re: Caravan off grid set up.

Postby Al510 » Sat Oct 27, 2018 2:18 pm

Just rading the manual for the sp pro, it has user definable settings for over and under voltage cut off and also for state of charge. With the inbuilt shunts to measure the DC loads as well, for state of charge, would this be enough protection for the lithium pack, if combined with this Cell level monitor? Or something similar?

https://www.evworks.com.au/zeva-8-cell-bat-monitor-v2
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Re: Caravan off grid set up.

Postby davidg » Sat Oct 27, 2018 3:27 pm

Al510 wrote:would this be enough protection for the lithium pack, if combined with this Cell level monitor? Or something similar?


Yes and No, yep that's sitting on the fence :)

The trick is that it depends on what you doing with it, for instance if you were to use with a 48V unit an LG or BYD pack they both have managed battery systems already and they will link in to th SP-Pro so they work together to do eaxctly what the battery pack wants.

If you were to use a DC charging system and the SP-pro was mainly an inverter and a charger when a generator is being used for some reason, one would expect you to at least link in some info to the SP-Pro otherwise it will not know a lot of what is going on. This is only part of the full explanation.

A BMS normally, not the SP-Pro would control cutoff points ie max DOD and max or peak charge point typically, while the SP-pro is very precise with voltages it is normally the job of a BMS on lithium to manage the actual battery SOC etc. It "tells" the SP-pro what it might want in a properly managed battery linkup such as an LG or BYD BMS there maybe a couple of others but I've forgotten which ones they are at the moment those ones certainly do tell the SP-pro exactly what is wanted via a CANbus link for LG and BYD packs, generally though at the moment for all this it is expected that it will be an AC coupled configuration.

If a BMS has some outputs they might be able to be linked to digital inputs inside the SP-Pro to do certain things.

Confusing isn't it :D . Don't worry its not simple with Lithium if you want a system that is DC coupled then what I mentioned about the SP-Pro and the LG, BYD packs will pretty much not work properly it assumes an AC coupled configuration is what is being used. I've not tested anything in this area, ie LG /BYD packs at the moment so I can't suggest any "undocumented" ways of doing things.
Last edited by davidg on Sat Oct 27, 2018 3:37 pm, edited 1 time in total.
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Re: Caravan off grid set up.

Postby Gordon-Loomberah » Sat Oct 27, 2018 3:31 pm

CALB or Winston? Either is probably ok. I took one CALB cell out a few years ago due to reduced capacity, and replaced it with a Winston, as CALB 400AH were no longer available. If I was buying now, I'd probably go with Winston, as they have a better range of capacities. A few of my cells have had odd behaviour since I installed them in 2012, but apart from the one I've removed, they still appear to have reasonably good capacity. I'd still go for a single string of larger capacity, rather than multiple smaller capacity strings, the connections are simpler and less expensive, and I don't think it really makes much difference to cell longevity.

I haven't run a BMS for over 4 years now, I just use cell balancer, details in a thread somewhere about my battery.
I do keep a close eye on my system though! I rely on the modified Latronics inverter LVD, which appears to be very reliable, and trust my 2 Outback FM80s not to take the voltage too high. I am only charging to 55.6V at the moment though (3.475V/cell, but usually reduce that slightly in summer), much lower than originally recommended by EV Power, and much lower than the voltage at which the EV Power balancers start to work, so they basically do nothing now.
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Re: Caravan off grid set up.

Postby Al510 » Sat Oct 27, 2018 3:53 pm

Thanks David, it is a bit confusing. So the charge profile in the sp pro is only used when plugged into a genny , and not when hooked up through the solar controller? So the solar controller is controlling the charge profile when the battery is being charged by solar? This would be for a DC coupled system. f thats the case, its a bit different than i thought. I was thinking it took all power sources and applied them through its programed charge profile.
The lithium i am looking at using are the individual cells from CALB or winston with no active BMS, just monitoring and voltage cutoffs , with manual balancing as required.
Thanks Gordon, I will look for your thread. I am sure i would have already read it though.
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Re: Caravan off grid set up.

Postby davidg » Sat Oct 27, 2018 7:44 pm

Al510 wrote:Thanks David, it is a bit confusing. So the charge profile in the sp pro is only used when plugged into a genny , and not when hooked up through the solar controller? So the solar controller is controlling the charge profile when the battery is being charged by solar? This would be for a DC coupled system.

Correct

Al510 wrote:If thats the case, its a bit different than i thought. I was thinking it took all power sources and applied them through its programed charge profile.

When a shunt is inserted into the NEG between of the MPPT charge controller and the batteries it does monitor the charge and the rate and if there is a link set between the SP-Pro and the MPPT charge controller depending on how it is connected it can trigger the controller to go to float or it could be the other way around, it will monitor SOC/DOD.

Al510 wrote:The lithium i am looking at using are the individual cells from CALB or winston with no active BMS, just monitoring and voltage cutoffs , with manual balancing as required.

You can get a smarter BMS to monitor the cells and send triggers ie go to float for instance which may have specific voltage and current setting for instance to the SP-pro via digital inputs, but ultimately the BMS controls what happens in Lithium and for that it needs to be smart, or you have to be the smart part of a BMS. I have built a couple of BMS's with triggers for LVD and HVD for lithium with dynamic balancing included, appears they work pretty well when installed on new cells from day one. However there are better options except for the dynamic balancing bit that are available but they do cost quite a bit, maybe well worth the cost though for a more automated system.
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