LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[john61ct]

Yes I thought the aesthetics might have been the main draw there.

Give it a go, someone's gotta be the pioneer 8-)

[gscriba]

Couple questions.
Anyone in the San Fran area willing and able to assist with the circuit built as is described in CNBs posts for the control of the HVC and LVC using my REC-ABMS and Blue Seas ML RBS 7700? I have ZERO practical experience with circuit building and though I understand the diagram, I have no idea how to implement. I have had my 12 volt 700 ah system up and running for about a month now and had one MAJOR scare by one MAJOR draw down. Don't want that to happen again so I need to correctly configure the "emergency" shut offs. I've been trying to learn/figure this aspect of my system, but I am not getting enough accomplished on my own.
I don't understand how to build the circuit as CNB very generously shared nor how to program of the REC-ABMS to then control the RBS 7700s.

So frustrating yet interesting to me. Anyone local to SF interested?

Purchased and received my two LG370Q1C-V5 panels, which will be mounted over my bimini. I'll be adding two additional 180-200 watt panels (still looking), which will slide out from under the LG's while anchored (slid and locked in/under the LG's while sailing). Planning on using Victron MPPTs, one per panel for redundancy with at least two over sized; in case one fails, two panels can be connected to one solar controller.

Building a stationary aluminum frame for the LG's that incorporates the below two smaller panel slide outs.

Thoughts regarding the plan for 4 MPPTs and size recommendations?
Thanks!

[newhaul]

Originally Posted by john61ct

Yes I thought the aesthetics might have been the main draw there.

Give it a go, someone's gotta be the pioneer 8-)

Wrong not the main draw. The main draw is an at a glance read of condition . But for the same price not having exposed wires is a definate plus.

If you were also running the gear you would have understood that without explanation.

[john61ct]

I have owned and use most of the top BMs on the market, so have not yet had a reason to try those. If I found the style you don't like to be more accurate than the one you do, I think it would be worth rigging a clean mounting option.

Maybe my next DIY portable powerpak I'll give them a try and post feedback.

And I'd really appreciate your stopping with the snide sniping please, about what you know nothing, and isn't even your business to know.

I'm not doing anything here but trying to be helpful.

[newhaul]

Originally Posted by john61ct

I have owned and use most of the top BMs on the market, so have not yet had a reason to try those. If I found the style you don't like to be more accurate than the one you do, I think it would be worth rigging a clean mounting option.

Maybe my next DIY portable powerpak I'll give them a try and post feedback.

And I'd really appreciate your stopping with the snide sniping please, about what you know nothing, and isn't even your business to know.

I'm not doing anything here but trying to be helpful.

not sinde or sniping.
I specifically asked for people with known experience . You have never posted anything concerning a specific system that you may or may not have and are utilizing therefore your input while helpful was not what I was looking for . Now if you wish to reveal what your full system is then I will revisit this specific situation.

[john61ct]

ha you funny

[evm1024]

I'm really confused now. I thought we were talking about battery monitors for hundreds of amp hour house bank systems and not DIY portable powerpaks.

Different animals. We are not talking about starting a diesel with a 2 to 4 second discharge. Not talking about charging up a RC plane battery or any other "small" application.

I thought we were talking about 150 amp discharge for hours or being able to charge with your full capacity for hours. (about 350 to 400 amps in my case not that I every go that far)

The battery monitor for those applications requires a beefy shunt that will not melt down 30 minutes into a charge or discharge cycle.

[newhaul]

Originally Posted by evm1024

I'm really confused now. I thought we were talking about battery monitors for hundreds of amp hour house bank systems and not DIY portable powerpaks.

Different animals. We are not talking about starting a diesel with a 2 to 4 second discharge. Not talking about charging up a RC plane battery or any other "small" application.

I thought we were talking about 150 amp discharge for hours or being able to charge with your full capacity for hours. (about 350 to 400 amps in my case not that I every go that far)

The battery monitor for those applications requires a beefy shunt that will not melt down 30 minutes into a charge or discharge cycle.

Yes i am talking about up to 50 amps in and up to 100 amps out at any given time. To run my big inverter. The unit comes with a 100 amp or a 350 amp shunt either will keep the accuracy in the 98 to 99% range.

Remember I'm only 29 ft

[john61ct]

Originally Posted by evm1024

I thought we were talking about battery monitors for hundreds of amp hour house bank systems and not DIY portable powerpaks

Sorry I wasn't clear.

100-300Ah in size

Portable in the sense of "lug to and from the other usage locations", e.g. island shack, campsite, maybe powering the dinghy.

Need for at least rudimentary Ah/SoC meter is the same, but you may not want to spend as much as you would for one more permanently installed.

The 1000A shunts get pretty unwieldy, so minimum size to cover the max discharge rate needed.

Charging 0.4-5C max, so usually lower than that.

[john61ct]

Originally Posted by newhaul

100 amp or a 350 amp shunt either will keep the accuracy in the 98 to 99% range.

Ah, if you mean as an ammeter ok.

I thought you meant accuracy of the SoC guesstimation.

[newhaul]

Originally Posted by john61ct

Ah, if you mean as an ammeter ok.

I thought you meant accuracy of the SoC guesstimation.

With my bank and usage it will serve quite well in any capacity i wish to ise it .

[evm1024]

Originally Posted by john61ct

Sorry I wasn't clear.

100-300Ah in size

Portable in the sense of "lug to and from the other usage locations", e.g. island shack, campsite, maybe powering the dinghy.

Need for at least rudimentary Ah/SoC meter is the same, but you may not want to spend as much as you would for one more permanently installed.

The 1000A shunts get pretty unwieldy, so minimum size to cover the max discharge rate needed.

Charging 0.4-5C max, so usually lower than that.

1000 amp shunt? Far too big for my usage. I only have the stock Victron 500 amp shunt on my house bank. The 1000 amp and larger shunts are designed more for off grid and grid tie applications with massive banks.

5C ? for a 300 ah suitcase pack that would be 1500 amps. 1500 amps at 13.8 volts is 20,700 watts. 20 KW. What kind of power supply are you thinking of? 20.7 KW at 120 VAC 172.5 amps. That's right up there with my entire house service panel rating.

How would you cool the thing while charging? Assuming it could take the charge rate that is a 300 ah bank fully charged in 12 minutes. That would be nice.

I imagine that the charger would cost more than the pack by far. Sounds like you are working on a commercial "solution".

What is your target market? RV, weekend boaters? Car campers?

Also, are you basing this on prismatic cells or cylindrical cells. What form factor? What BMS? Heck will it be ABYC compliant when (if not already) the LiFePO4 standard is out.

Nice that you have already got at least one built. Prototype or general testing? Any chance that you will give Battle born a run for their money?

Data!data!data! he cried impatiently. I can't make bricks without clay.'

Originally Posted by john61ct

Maybe my next DIY portable powerpak I'll give them a try and post feedback.

I've tried out 3 of the "China made" monitors. I suggest caution here given your intended charger/discharge rate.

With the (lack) of accuracy I've measured it is quite possible to over or under charge at least one cell in your pack. And with repeated charge/discharge cycles going into the knees it would be easy at those rates to get wildly out of balance and have a cell end up above 4 volts or below 2 volts. Also, active shunting is not very effective at high charge rates. Just too little both in terms of bypass current and time.

You might consider rolling your own using any of the current crop of AFE. Take a look at the TI bq76925 for starters (man I wish I had one of those when I worked for Intel. I ended designing with a bunch of discrete FET switches and caps for a 20 channel sample and hold feeding a 16 bit ADC - ages ago, far, far away)

Anyway keep us posted on your progress.

[MikeFergie]

I have one of these units and find it very good. The only thing I don’t like is the fact that the shunt is loose IE the bolts going though it are loose and the shunt doesn’t come with a housing to screw it down. But it works if you use a copper bar off the negative direct to the shunt which supports it.

I also have a victron BMV 712 ( changed over from the 700 recently) and find for $250 the victron is expensive and does not warrant the massive price difference.

Ps get the 300amp shunt not the 100amp shunt

Rgards
MikeF

Originally Posted by newhaul

Ok guys for those that are actually using Lfp and a shunt type battery monitor I need input.
I'm thinking of adding one but most are to expensive to be considered by me
So I need opinions on this monitor
https://www.aliexpress.com/item/3294...7764499cqd2JU0

[newhaul]

Originally Posted by MikeFergie

I have one of these units and find it very good. The only thing I don’t like is the fact that the shunt is loose IE the bolts going though it are loose and the shunt doesn’t come with a housing to screw it down. But it works if you use a copper bar off the negative direct to the shunt which supports it.

I also have a victron BMV 712 ( changed over from the 700 recently) and find for $250 the victron is expensive and does not warrant the massive price difference.

Ps get the 300amp shunt not the 100amp shunt

Rgards
MikeF

mike thank you for the information it was just what I was looking for.
I fully intended to get the 350 amp shunt just in case I ever need to draw more than .5C out of my bank . Or I ever upsize the bank beyond the current 240ah as to the shunt I have access to a 3d printer so I can design a plastic base to securely mount the unit to the bulkhead .

Now the real question
before or after the bms? I'm thinking before ( on the battery side )

[SweareDeep]

Originally Posted by gscriba

Couple questions.
Anyone in the San Fran area willing and able to assist with the circuit built as is described in CNBs posts for the control of the HVC and LVC using my REC-ABMS and Blue Seas ML RBS 7700? I have ZERO practical experience with circuit building and though I understand the diagram, I have no idea how to implement. I have had my 12 volt 700 ah system up and running for about a month now and had one MAJOR scare by one MAJOR draw down. Don't want that to happen again so I need to correctly configure the "emergency" shut offs. I've been trying to learn/figure this aspect of my system, but I am not getting enough accomplished on my own.
I don't understand how to build the circuit as CNB very generously shared nor how to program of the REC-ABMS to then control the RBS 7700s.

So frustrating yet interesting to me. Anyone local to SF interested?


Thanks!

REC-BMS sell a Bistable Latching Relay Driver which, I think, does what you want. It's listed under Accessories on their website.