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Old 18-03-2010, 15:42   #166
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Hi, Tinkerer, and welcome to CF. Of course, you bleeding-edge racing types would want this sort of thing! For my part, as a member of the more conservative (i.e., "cheap") cruising bunch, I'm thankful for your interest and look forward to hearing about your experience with it.

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Old 18-03-2010, 15:48   #167
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I have been wondering about is the need to fuse the battery to engine side of things when switching to these batteries. Many boats do not have any fusing in this curcit.LiFeP04 batteries can supply an enormous discharge current without their terminal voltage dropping much. That is a lot of energy in a fault situation.
Also is the interrupt rating of the fusing on the domestic battery side needs to be considered.
Will the BMS provide protection? A lot of energy will be released before the LVC is reached.
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Old 18-03-2010, 16:12   #168
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We don't have a fuse between starter battery and starter/alternator but do have fuses on the alternators that charge the house bank.

You also have the main fuse on the battery bank itself... have you??!! you should and it should be a class-T and provide protection for the scenario you describe. The fuse on the alternator is to deal with trouble during charging with the alternator.

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Old 18-03-2010, 17:03   #169
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Originally Posted by s/v Jedi View Post
We don't have a fuse between starter battery and starter/alternator but do have fuses on the alternators that charge the house bank.

You also have the main fuse on the battery bank itself... have you??!! you should and it should be a class-T and provide protection for the scenario you describe. The fuse on the alternator is to deal with trouble during charging with the alternator.

ciao!
Nick.
Yes the house battery banks are fused with ANL fuses. Their interrupt rating is 6000A which blue seas quote as " meets ABYC requirements for main DC circuit protection on large battery banks". I have some extra reserve because my house system is divided into 2.
I think the higher interrupt rating of class T fuses (even if they are difficult to buy in out of the way places) will be necessary for Lithium and I wonder if these will provide adequate protection.
My concern was, however, the start battery bank which is often not fused at all.
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Old 18-03-2010, 18:08   #170
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Originally Posted by noelex 77 View Post
Yes the house battery banks are fused with ANL fuses. Their interrupt rating is 6000A which blue seas quote as " meets ABYC requirements for main DC circuit protection on large battery banks". I have some extra reserve because my house system is divided into 2.
I think the higher interrupt rating of class T fuses (even if they are difficult to buy in out of the way places) will be necessary for Lithium and I wonder if these will provide adequate protection.
Let's hope so, I don't know much above 20,000A interrupt rating!

But also, you shouldn't just look at what ABYC says because they have to deal with it in general terms. If the bank that the fuse is protecting can supply more than 6,000A you should step up to class-T. ABYC might not have imagined banks that big but today a single Odyssey can do 5,000A already so just two of those parallel really need a class-T already.

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My concern was, however, the start battery bank which is often not fused at all.
Yes and I prefer it that way (ABYC allows this). I have two of those Odyssey batteries as my starter bank so this part of the wiring must be absolutely rock solid. If anything goes bad the starter or alternator will melt a winding but the problem would have been in there already. Think of those windings as the fuse ;-)

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Old 18-03-2010, 18:58   #171
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My biggest concerns are:
1) How long will the batteries really last?
2) Can they really be charged from 20% to 90% at constant rate of about 0.3C with LA chargers/regulators?
3) Will they be damaged with keeping a long term float voltage of about 3.3V/cell on them?

Doug
Doug,

1) There is very good evidence that LFP banks can last 2000 cycles when in good care, even if you don't believe manufacturer's claims of 3000-5000 cycles. I know of people using LFP in EVs for over 3 years without any signs of degradation. House bank usage is even less stressful than EVs.
2) Yes, this has been proven beyond any doubt by countless DIY EVers , including myself.
3) Its impossible to damage LFP at 3.3V. You can hold this voltage forever since there is zero current flowing at that voltage level.

Hope this helps.
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Old 18-03-2010, 19:04   #172
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I just checked the Genasun marine product and found it is flawed. It will break the connection between AC charger and battery pack in case of HVC which will result in expensive damage to the charger (diodes will blow).
FWIW, I believe they intend for you to cut off the AC charger's current with a solenoid on the AC side, as you later described.

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a HVC should turn the charger off, disconnect solar panels, switch wingen output to dump load and interrupt field current to alternators. Nothing more, nothing less.
I would add shut down the genset for those so equipped.

Am I right in thinking that you'd only need to take these actions if you have one bank? With two banks in parallel, could you just break DC input from the charge sources to that one bank. With the other bank soaking up the current, it shouldn't hurt diodes on the alternator or AC charger. Of course, then the BMS would still have to cut out charging sources if both banks went to HVC.

Personally, I think we still need to be concerned about handling HVC on LFP battery banks even if at first blush our charging sources wouldn't be able to overload a 12V nominal bank. Stuff happens!
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Old 18-03-2010, 20:42   #173
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FWIW, I believe they intend for you to cut off the AC charger's current with a solenoid on the AC side, as you later described.
Maybe that is so but they didn't write that in the manual I think. The diagram doesn't show it.

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I would add shut down the genset for those so equipped.
No, the genset is either outputting DC using an alternator or it is feeding AC to a charger. In the AC scenario it is likely that the genset is feeding other devices as well so you don't want it to turn off on HVC.

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Am I right in thinking that you'd only need to take these actions if you have one bank? With two banks in parallel, could you just break DC input from the charge sources to that one bank. With the other bank soaking up the current, it shouldn't hurt diodes on the alternator or AC charger. Of course, then the BMS would still have to cut out charging sources if both banks went to HVC.
Yes, this has me puzzled. This mechanism will probably work in case of a cell in one bank develops a short, but not otherwise because the lower SOC bank will take all/most of the current until it's equal with the other one (lower internal resistance). But then again, with a 14.2 charging voltage and no cell failure, HVC isn't going to happen. I think Genasun is counting on this and I think they may be right. What's left is their statement that the system will balance on the fly which I can't see working with just 14.2V charging voltage.

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Personally, I think we still need to be concerned about handling HVC on LFP battery banks even if at first blush our charging sources wouldn't be able to overload a 12V nominal bank. Stuff happens!
Exactly.

cheers,
Nick.
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Old 19-03-2010, 06:26   #174
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Let's clarify the very unlikely scenario of one cell in a string developing a short. You are concerned that it will cause HVC on the rest of 3 cells since the voltage will be distributed. Yes, this is logical, but you are forgetting one thing. Shorted cell will immediately cause hard LVC before any chance of adjacent cells get to HVC. Remember, BMS is on a cell level, not a bank level. Bank with shorted cell must be removed from the circuit immediately and never used again until repaired. Shorted cell is a safety hazard, even though LFP cells don't catch fire, they can still melt from the heat and cause a mess. Mind you, not as bad of a mess as shorted LA cell, with acid spewing and hydrogen releasing, but still an unpleasant situation which must be dealt with.

I couldn't sleep last night, processing all the data you guys are feeding me

I am thinking of a BMS which would distinguish 4 types of events, as follows:

1. Soft HVC. This happens when any cell gets to 3.625V ( 14.5V per bank of 4 cells ). This triggers low voltage relay which can be used to drive charger controls ( alternator field, AC relay, whatever ).
2. Hard HVC. This happens when any cell gets to 3.8V. This means something has gone terribly wrong and we must act fast by opening the circuit even of that means blown diodes somewhere else. This is last resort and can be made optional, depending on where user wants to put a risk, choose blown diodes over blown battery.
3. Soft LVC. This happens when any cell gets to 2.7V ( 10.8V per bank of 4 cells ). This triggers low voltage relay which can drive the buzzer or light or small electroshock in the captain's seat, whatever it takes to bring attention. By this time your existing battery monitors will be screaming anyway since they think your LA bank is dead.
4. Hard LVC. Any cell gets to 2.5V or less. Again, something has gone wrong and we cut the battery from the circuit.

Remember, BMS will be integrated with the battery, not a separate box. So its up to the customer how to integarate soft controls with the rest of the boat, regardless of that, hard controls will be there to protect the battery from abuse.

Your thoughts?
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Old 19-03-2010, 07:28   #175
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Hi Electric,

Sounds good. But I'd like to get to the bottom of these HVC/LVC events. LVC disconnects load, right? So after that's done, we still are going to get HVC from the other 3 cells, disconnecting the charger? It should because it really is a HVC for the other 3 cells.

Hard HVC/LVC should be triggered on fixed values and the soft versions should be adjustable. There are so many different chargers out there and you never know what their maximum voltage output is while we do want to trigger a soft HVC as a "charging ready" signal. This is the only automatic way to stop charging with chargers that don't know about LFP chemistry. I still need to look into the programming of the Victron charger to check the claim that it can be programmed to charge LFP correctly.

cheers,
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Old 19-03-2010, 08:28   #176
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Hi Electric,

Sounds good. But I'd like to get to the bottom of these HVC/LVC events. LVC disconnects load, right? So after that's done, we still are going to get HVC from the other 3 cells, disconnecting the charger? It should because it really is a HVC for the other 3 cells.
No. My current thinking for a drop-in LFP replacement is not to have separate terminals for charger and load. The battery box would have 2 terminals just like any LA battery. Hard LVC/HVC events would be considered catastrophic and will open internal contactor to save the battery (soft control will be triggered first to save the alternator diodes of course). If you encountered hard LVC, then you can't possibly get HVC from other cells. Unless one cell is dead you can't possibly encounter LVC and HVC from different cells in the same bank.
Quote:
Hard HVC/LVC should be triggered on fixed values and the soft versions should be adjustable. There are so many different chargers out there and you never know what their maximum voltage output is while we do want to trigger a soft HVC as a "charging ready" signal. This is the only automatic way to stop charging with chargers that don't know about LFP chemistry. I still need to look into the programming of the Victron charger to check the claim that it can be programmed to charge LFP correctly.

cheers,
Nick.
Although I don't disagree on principle, I don't see how this is relevant assuming all charging sources were built for LA batteries. Since LFP operating range overlaps LA range, there is no issue with existing charging
sources and there is no need to reprogram anything. LFP charging curve is simple CC/CV and can be stopped at any point without reaching CV.
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Old 19-03-2010, 08:45   #177
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I just checked the Genasun marine product and found it is flawed. It will break the connection between AC charger and battery pack in case of HVC which will result in expensive damage to the charger (diodes will blow).
Instead, a HVC should turn the charger off, disconnect solar panels, switch wingen output to dump load and interrupt field current to alternators. Nothing more, nothing less.
I talked about this issue with Alex at Genasun and in our type of application, that relay should be wired to either : 1. the field coil or regualtor input of the alternator or 2. the input side of the charger

Quote:
I understand the problem in that every charger is different and some will not allow a remote shut-off signal. In that case one could insert a relay on the AC input of the charger and switch it off that way. If you disconnect charger output while charger is active, diodes blow just like with the alternator. I tested this (fuse blew, Freedom30 ruined).
Bummer!


Quote:
When all is okay, this won't happen, but we don't need the BMS for when all is okay; we need it when something is wrong. When we charge 4 LFP cells in series with 14.2V and one cell develops a short, the other cells WILL cause an HVC event while charger is at high output with a lot of damage as the result.

On balancing: Genasun claims on the fly balancing with 14.2V charge voltage for a 12V system. This translates to 3.55V per cell and I have the feeling that this is too low for balancing.
They can adjust it for cell chemistry. thundersky cells are maxed out at 4v/cell, sky Energy at somewhat less IIRC. for us with the stock (dumb) regulator max charge voltage is 3.875V/cell. the voltage sense circuit would be adjusted for this (I'll confirm before install)


Quote:
See, you don't understand it yet. When there are just some Indians peddling their cayuko's around your boat, there is not going to be any electrician you can pay to fix it.
I agree that by following a well defined & written procedure, cruisers will be able to fix it themselves if they have that power supply aboard... which they don't have now. I also think a DC-DC converter would be much better than a bench PSU for a boat.
hence Green motion's dc/dc convertor sets.

Quote:
What I do like about the Genasun product is the "two batteries" setup. That might actually be their solution for interrupting charge circuit without blowing diodes because each battery has it's own set of relays on input/output.

I've been studying LFP & available solutions for the past days and I am convinced much better products for using it on a boat will come. I think I'll jump in and buy some cells to play with.

cheers,
Nick.
good show! I'm with you that a better solution may be forthcoming- the technology is still pretty new.
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Old 19-03-2010, 12:16   #178
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=

Yes and I prefer it that way (ABYC allows this). I have two of those Odyssey batteries as my starter bank so this part of the wiring must be absolutely rock solid. If anything goes bad the starter or alternator will melt a winding but the problem would have been in there already. Think of those windings as the fuse ;-)

cheers,
Nick.
I agree this is the way my start bank is set up also. We know this is reasonable and safe because of experience with not only boats but cars and trucks. This history and experience (and the ABYC guidelines) is all with conventional lead acid batteries.
We need to develop new experience with Lithium batteries, the asset of their very high current delivery, may turn around and bite us in a fault situation. What is the interrupt rating of your alternator windings?
Appropriate circuit protection is not expensive or difficult, but I think those installing these batteries need to give the matter some thought.
Fusing all circuits employing lithium batteries (including engine batteries) with T class fuses would be my choice.
Not many boats are wired this way at the moment.
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Old 19-03-2010, 13:41   #179
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In the case of one cell shorting out, leaving the remaining cells susceptible to overvolt damage during charging, couldn't you attack the problem in the same way that you would attack overcharging in any situation?

i.e. Ignore the electrical situation, and use a set of thermal sensors on the batteries. If the battery temperature (one sensor on each cell) rises, 10C or 15C above ambient (whatever the threshold needs to be) the thermal protection should scram the entire charging system. Doesn't matter why the cells are getting hot, any hot cell(s) are something that a good protection system needs to take into account. And, thermal sensors are basically cheap. It should be easy to daisy-chain them and have them cut off charging with one circuit.

From what I'm reading elsewhere, a problem with LFP cells is that it is hard to determine their discharge state unless current monitoring circuitry is added, which means shunts and microprocessors, and either bypassing or "reregulating" existing charge controllers though.

Sounds like a no-brainer for the serious racers though, a fast way to drop half the lead off a boat.
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Old 19-03-2010, 15:37   #180
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In the case of one cell shorting out, leaving the remaining cells susceptible to overvolt damage during charging, couldn't you attack the problem in the same way that you would attack overcharging in any situation?
Again, you are missing the point. If cell is short, that's it, we are done, nothing else matters. No sense in checking anything else, just gracefully disconnect the charging source and drop the contactor.

Quote:
If the battery temperature (one sensor on each cell) rises, 10C or 15C above ambient (whatever the threshold needs to be) the thermal protection should scram the entire charging system. Doesn't matter why the cells are getting hot, any hot cell(s) are something that a good protection system needs to take into account. And, thermal sensors are basically cheap. It should be easy to daisy-chain them and have them cut off charging with one circuit.

From what I'm reading elsewhere, a problem with LFP cells is that it is hard to determine their discharge state unless current monitoring circuitry is added, which means shunts and microprocessors, and either bypassing or "reregulating" existing charge controllers though.

Sounds like a no-brainer for the serious racers though, a fast way to drop half the lead off a boat.
My head is exploding with ideas and features that I would add to those base 4 functions I listed earlier. I could add thermal management, current sensor to trip the BMS if current is dangerously high, like 3C, for a specific time period, etc etc

Today I made a decision to design new BMS using microprocessor based controller, which will be integrated with 4 200AH cells in a marine battery box and will be a drop-in replacement for 200AH Lead Acid battery. I am still gathering features and components that I want to implement. This will be designed specifically for boater's needs, but I suppose it could also work in RVs and some stationary applications.

Do you guys think its worth starting a new thread to collect all desired features and functions in one place and stay on the subject of my specific project, while keeping this thread for general LFP discussions?
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