Combined Pb acid Battery with LiPo project

[fryedaze]

Started Fryedaze LiFePo mod today. Off loaded 8 golf cart batteries with 440 amphrs of capacity with two 460 amphr Epoch Essential batteries. 520 lbs replaced with 168 lbs snd twice the capacity. Demo was done today, but tomorrow will start rebuild.

 

[fryedaze]

Started Fryedaze LiFePo mod today. Off loaded 8 golf cart batteries with 440 amphrs of capacity with two 460 amphr Epoch Essential batteries. 520 lbs replaced with 168 lbs snd twice the capacity. Demo was done today, but tomorrow will start rebuild.View attachment 161284View attachment 161285

 

[dhays]

I have the same batteries installed. Unfortunately, I haven't had much of a chance to test them out, but so far they seem to be doing well.

What is the "Battery Manager" you show in your schematic?

 

[fryedaze]

BankManager

NOW AVAILABLE BankManager™ System Combine Lithium (LiFePO4) and Lead-Acid Batteries in the same system, and charge everything optimally. Introducing the BankManager. BankManager™ technical manual and user information here Frequently Asked Questions (FAQs) Buy BankManager™ In January 2021...

18acab-04.myshopify.com

 

[fryedaze]

We had to hit pause on the project. Light flash in left eye peripheral vision. Maybe retinal tear. Should be back at it in a few days. Getting old is a challenge

 

[fryedaze]

Preliminary component lay out.

 

[fryedaze]

Started wiring today. The system is simple to install. There is an interface connection box that allows all in inputs from the CT, Contactor and Temperature probe to connect to. The interface block has two Cat 5 connections that run to the Bank Manager. The BankManager monitors the Pb and LiPo batteries. It only does one thing. It controls the contactor when it determines if the Pb and LiPo should be connected or disconnected. The contactor will isolate the LiPo if they are at full charge. It will also float the Pb batteries if there isnt a charge source.

 

[fryedaze]

95% complete. Everything is connected with the exception of a positive jumper between the LiFePo batteries and the Cat 5 communication cables to the Bank Manager control box. I have kept the jumper off as a safety measure. Final tie in is next and I will see how it works.

 

[NoRain]

Um, I’m not seeing a Class T fuse anywhere close by?

 

[fryedaze]

Each positive battery terminal has a 300 amp fuse and the negative output has a 300 amp fuse.

 

[NoRain]

Yes I see that, but MRBF fuse is not sufficient, and does not meet ABYC spec. Needs to be Class T or better. Your batts are the Essential model, yes? As far as I am aware the Essential is not internally fused like the Marine 460 (now the Elite V2). You may wish to confirm that with Epoch.

 

[fryedaze]

I would be interested is more info on this.
Blue Seas indicates they are ABYC compliant.

Requires the use of Terminal Fuse Blocks PN 5191 or PN 2151—do not mount the fuse directly to the battery terminal
Interrupt rating satisfies ABYC requirements for DC Main circuit protection on large battery banks
Ignition protected—safe for installation aboard gasoline powered boats
Clear window—visual indication of blown condition
Color coded for each amperage

 

[tiltrider1]

I don’t have an ABYC manual close by to confirm. I do know that with the amount of amperage you are dealing with you need a fuse that has the ability to not get welded across. I don’t remember the correct technical term for destructive resistance. I am sure some one will jump on and give the correct terminology.

 

[NoRain]

Yeah, I’ve seen that statement on Blue Sea’s site. It is too vague for my taste - ie what *exactly* is their definition of “large battery bank”.

ABYC says (paraphrased), the AIC rating of your fusing must be greater than the Short Circuit rating of your battery bank. As an example that some may find surprising, I have three pairs of Odyssey AGM’s for bow thruster, stern thruster, and starting bank. The Short Circuit rating of each battery is over 5000 amps, therefore a parallel pair is over 10,000 amps! So I have Class T’s on those three banks. Also on my house bank of 3 pairs of L16 AGMs (short circuit rating on that bank is well over 15,000 amps). I don’t know what the SCCR is for your Essentials, but that is what you need to determine. But if you take the BMS out of the equation (more about that below), the SCCR of LiFePo battery is absolutely enormous.

But there’s a twist - the BMS, and that is a rapidly involving situation that I don’t think is addressed yet by ABYC. Batteries like yours with modern built-in BMS’s are claiming the BMS can provide “sufficient” over-current protection by themselves. I don’t know the details of the claims - you can bet they are quite technically complicated and hotly contested - but that’s something you’ll need to satisfy for yourself. Maybe talk to Epoch? At the moment, AFAIK ABYC does not consider the BMS to be a “replacement” for Class T fusing. I can say that if it was me (and it will be in a few months) I would not install that bank without Class T fusing. In fact if I go with the Epoch Elite V2 which is quite likely, I’ll leave my Class T fusing in place. Belt and suspenders and a piece of rope tied on as well, if you will .

Here’s a snip of the ABYC advice:

 

[fryedaze]

Looks like the AIC is 10000 amps in the 300 amp MRBF .

 

[NoRain]

Yes it does. But that is not sufficient IMO. The SCCR of your battery bank could easily be 20,000 amps. I don’t know, I didn’t see a spec for it on Epoch’s site. So as I explained above, you’re going to have to make your own decision and be comfortable whether you will put your faith in the claims made for the BMS to provide sufficient over current protection. Again, in my opinion we are way too early in the life and experience span for these BMS’s to make reasonable judgements on whether they really do provide that level of of protection and safety, and the potential power release that we’re talking about is too enormous to take any chance. So to repeat, if I was in your shoes (and soon will be) I would/will absolutely be using Class T fusing.

BTW, AIC rating is not related to the fuse size. The 30A MRBF fuse has the same AIC rating as the 300A.

 

[fryedaze]

Thanks for the input. I have 3 fuses on two batteries in parallel. Each battery has a fuse on the positive terminal and the output neg terminal has another. Only one needs to isolate the bank. Its a safe setup.There is a 250 amp ANL on the inverter , a 300 amp ANL between the Li and the Pb bank.

 

[twistedtree]

NoRain is correct, and this had been revised in the upcoming version of E-11 that should be published later this year. I think the short answer is that you need a fuse with a minimum 20,000A AIC rating, which in practice means Class T. There are also rules for paralleled batteries saying when you need to break them into smaller fused groups, again to meet AIC requirements. A BMS is never a substitute for the fusing requirement. And a manual battery switch is still required for any/all battery banks.

 

[fryedaze]

I am interested in some feedback on calculations done on short circuit current for two Epoch Essential 460amphr batteries in parallel.
Epoch says the internal resistance is 30 milliohms (.003 ohms). In parallel the bank has a resistance of .0015 ohms (1/R + 1/R = 1/Req).
I=V/R. 8800amps = 13.2v /.0015.
Looks like short circuit AIC would be 8800 amps.
I am doing more research on fusing requirements. Some Internet info ( for what its worth) says short circuit current could be 20-30K amps on LiFePo. They may be considering 24v or 48v systems.
The latest Epoch 460amphr battery has an EV industry fuse with a 50000 AIC rating internal to the Battery.
Any input would be appreciated.

 

[fryedaze]

NoRain is correct, and this had been revised in the upcoming version of E-11 that should be published later this year. I think the short answer is that you need a fuse with a minimum 20,000A AIC rating, which in practice means Class T. There are also rules for paralleled batteries saying when you need to break them into smaller fused groups, again to meet AIC requirements. A BMS is never a substitute for the fusing requirement. And a manual battery switch is still required for any/all battery banks.

Thanks, looks like I will be adding a manual batt switch. I incorrectly assumed that the Bank Manager contactor would be my discount. It has a remote switch if needed.
Live and learn.

11.6.1.2.1 A battery switch shall be installed in the positive conductor(s) from each battery or battery bank with a CCA rating greater than 800 amperes or 100 Ah if CCA is unavailable.

 

[Marco Flamingo]

I have been going through a similar process of trying to understand the fusing requirement of 2 banks of two 280Ah LFP in parallel. I haven't contacted my battery manufacturer yet and the necessary short circuit info doesn't seem to be on the website(s) for the battery. Frustrating that manufacturers repeatedly state that LFP are lighter than lead but don't state the basic information required for safely using their product.

Class T fuses have been the gold standard for battery banks, but that was for lead. A "largish" bank of LFP can easily exceed the Class T AIC rating. My 2 banks will be separately fused, but I'm still uncertain whether 2 x 280Ah LFP exceeds the Class T rating. The next common fuse rating seems to be 50K, but I haven't found a "package system" that seems as convenient as Class T. Most are knife blade fuses that require a fuse puller and lack any type of protective cover. That means the two fuses would require an electrical box. Definately more complex fusing than I originally planned.

To add to the complexity is the changing world of DC fuses caused by electric vehicles. China is now producing several lines of DC breakers with high AIC ratings and in the 200-400 amp range. One that I was looking at (for less $ than a Class T and holder) has a 50K AIC, but in an interesting configuration. It is rated to disconnect at the breaker for 35K AIC and be resettable. It will disconnect up to 50 AIC, but that may trigger an additional safety break feature that is not resettable. I think a 35K AIC on a 200A breaker has me covered.

The breaker is ISO certified and has other EU certifications, but not UL. It seems the emerging trade war has created certification issues. I read that UL listings are not acknowleged in China and China's certification system is not recognized in the US (until such time as a US company rebrands them and has them UL certified). Welcome to the trade wars. Just what we needed is a more complex fusing calculation.

 

[NoRain]

@fryedaze & @marco - just another thought or two. As you’ve seen and heard there are still some gaps in specs that we have to live with. Here’s another, but at least it’s a helpful/hopeful one. You may have noted in various specs that the AIC for a fuse architecture is higher at lower voltages. But I haven’t seen a curve that would tell exactly what at what voltage, other than the one(s) that it is rated and tested at. To use a specific example - the Blue Sea Class T is rated at 20,000 AIC at 125 VDC. That suggests that its AIC at 12.8 VDC should be higher; MUCH higher. How much? Don’t know, no curve. As far as I’ve been able to determine it only has that one test point. Any extrapolations are up to you. Another eg, I forget the manufacturer but their rating was at like 58 VDC or some such odd number. Don’t know why, but…. The point of this is that you may take some comfort that the Class T should be amply capable of dealing with multiple LiFePo batteries in a bank. How many? Don’t know Personally I’d be comfortable using one Class T to protect a bank of 3 x 300AH Epoch Essentials. If you are not comfortable with that extrapolation, you could put a Class T on each battery. Or as Marco observes look at some of the real big industrial product. But disclaimer: this is not advice to go out and do that, just to share some thoughts to help you form a framework of comfort and/or do some research to get that comfort.

 

[NoRain]

The latest Epoch 460amphr battery has an EV industry fuse with a 50000 AIC rating internal to the Battery.
Any input would be appreciated.

The original Epoch Marine 460 had that internal fuse, as well as the new V2. The Essential does not.

 

[Marco Flamingo]

The original Epoch Marine 460 had that internal fuse, as well as the new V2. The Essential does not.

Yes, a 50K AIC internal fuse for a single 460Ah battery. That's part of what makes the whole exercise so frustrating. Back when (only a couple years ago) 100Ah LFP was by far the most common size, there was some testing of short circuit current. Results varied wildly from 1,000 to 3,500 amps, probably because, in addition to the battery's internal resistance, lug connections, wire resistance, etc. also effects the test results. To make things more complicated, there is no real consensus on what 200Ah, 300Ah, 400Ah, etc. LFP batteries can produce. The only consensus is "more." Some use the overly simplistic multiplication rule of thumb that if 100Ah is possibly 3,500 short circuit amps then a 600Ah bank is possibly 21,000 amps. Goodbye Class T; we hardly knew you.

To further complicate matters, 600Ah from a bank of 6 100AH batteries would have more resistance because of the cabling, whereas 600h from 2 x 300Ah batteries would have less resistance, therefore higher short circuit amperage. How much more? Same with trying to interpolate what a 20K AIC fuse rated at 150V translates to for a 12V system. More, but how much more? We seem to be stuck with the WAG method of fusing. Not good on a boat.

 

[SteveK]

ABYC says 256-500 Ah has a 5000 AIC
As each battery has a 300A fuse rated for 10,000 AIC Help me understand what is the problem?

 

[fryedaze]

Attached link is a short video of the system. Please excuse our messy 36 year old boat.

 

[luna]

I am interested in some feedback on calculations done on short circuit current for two Epoch Essential 460amphr batteries in parallel.
Epoch says the internal resistance is 30 milliohms (.003 ohms). In parallel the bank has a resistance of .0015 ohms (1/R + 1/R = 1/Req).
I=V/R. 8800amps = 13.2v /.0015.
Looks like short circuit AIC would be 8800 amps.
I am doing more research on fusing requirements. Some Internet info ( for what its worth) says short circuit current could be 20-30K amps on LiFePo. They may be considering 24v or 48v systems.
The latest Epoch 460amphr battery has an EV industry fuse with a 50000 AIC rating internal to the Battery.
Any input would be appreciated.

I had a quick look at this and provide the following feedback. Seems most other readers overlooked a few things.

- If the internal resistance of each battery is 30 mΩ, that is 0.03 Ω. Not 0.003 Ω
- If we rely on these two batteries to act like two resisters, the bank resistance becomes 0.015 Ω
- To correct your result just knock a zero off, your battery short circuit current of 8,800 Amps becomes an Isc. of 880 Amps.

This revision seems to move things in the opposite direction compared to what ABYC and others are saying. In addition there must be something wrong when you consider that according to Epoch each of the 2 batteries is said to be able to deliver a Peak/Surge current of 1,200 A. With an Isc of 880 A, how?

I think a few things are at issue here.

- Epoch says the internal resistance for each battery is less than or equal to 30 mΩ. Epoch does not state the minimum resistance. A smaller resistance makes the current larger.
If the battery bank acted like a resistor with 1 mΩ resistance the Isc through the pair of batteries would, at your 13.2 volts be 26,400 Amps.

- Epoch also calls this 30 mΩ the Internal Impedance of the battery and is obtained by use of test equipment operating at 1kHz AC on a battery at 50% SOC. This appears to be a standardize test. One has to wonder what is the purpose of this 30mΩ value, why is it important. It does not seem to result in the correct Isc values. Not even in the same ballpark.
Maybe it's useful somewhere else. Maybe the calculation of battery resistance is just not that simple.

- I have not checked many of them, but battery manufacturers do not seem to provide Isc values for their products. You could easily think it is large as Epoch installs a fuse with an AIC of 50kA. This leaves the user in most instances to come up with their own assessment of Isc for use in selecting the required fuse. Not a good situation.

Bottom line, as I'm still in lead, my Class T is likely fine. Unless, when I change to LFP there is a lot more info. available, I will likely move to a NH or other series of fuse.

 

[luna]

ABYC says 256-500 Ah has a 5000 AIC
As each battery has a 300A fuse rated for 10,000 AIC Help me understand what is the problem?
View attachment 161634

Steve

To help you understand the problem, read Note 2.

 

[fryedaze]

I had a quick look at this and provide the following feedback. Seems most other readers overlooked a few things.

- If the internal resistance of each battery is 30 mΩ, that is 0.03 Ω. Not 0.003 Ω
- If we rely on these two batteries to act like two resisters, the bank resistance becomes 0.015 Ω

Well I screwed that up. Now nothing makes sense. I am punching above my weight class.

 

[NoRain]

There is some very good (and recent) discussion on this here "Victron Comms" Epoch 460AH Lifepo4 8D Marine batteries. Sums up nicely what I am taking too many words to try to explain.

Without a specific statement from Epoch or any of the other manufacturers on *exactly* what the short circuit current rating is for their batteries we are left to draw our own and best conclusions. And without that number I’ve pretty much offered all I can on the subject so will probably step away from this discussion. Good luck to all.