Mikedefieslife
Member
Where did you get your hex head threaded rod studs from? They seem very rare in stainless.
270ah DIY LiFePO4 build
- Thread starter Poey50
- Start date
Zing
Well-known member
I actually disconnect using my alternator field wire, which is blue. No problems so far. I was concerned that Collins said that was a bad plan, but could find nothing on his site to support what you say. Can you provide further information please?
Poey50
Well-known member
I got mine from Amazon - very cheap and marine stainless. M6 x 30mm.
XunLiu 316 Stainless Steel Internal Hex Socket Cup Point Grub Screw (20, M6X30): Amazon.co.uk: DIY & Tools
Poey50
Well-known member
This is specific to the connection between the MC614 and Balmar. It was on the 'Lithium Batteries on a Boat' Facebook group. Some weeks ago that it first came up and then again recently (this week) when I raised it. If you search there under his name you should find the quote. He was very clear on that point.
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Poey50
Well-known member
Zing - I've dug out the Rod Collins quote in case you aren't on that group. This is from September 14th ...
"Cutting the field on the Balmar regulators is not a suitable method and can actually damage the regulator. For a BMS the best method is the red wire as this is an instantaneous cut/shut down and if the BMS has enough hysteresis for an alternator shut-down the BMS will cut off safely and not create a load dump. For a manually activated dash mounted shut-down switch use the brown ignition wire."
He is talking about a BMS shut down but the same would apply to a manual switch which is what I have installed for those occasions when I don't want charging with the engine running. When previously discussed on that group he said that the designer of the MC614 had in mind the red power wire as the one for safe disconnect.
"Cutting the field on the Balmar regulators is not a suitable method and can actually damage the regulator. For a BMS the best method is the red wire as this is an instantaneous cut/shut down and if the BMS has enough hysteresis for an alternator shut-down the BMS will cut off safely and not create a load dump. For a manually activated dash mounted shut-down switch use the brown ignition wire."
He is talking about a BMS shut down but the same would apply to a manual switch which is what I have installed for those occasions when I don't want charging with the engine running. When previously discussed on that group he said that the designer of the MC614 had in mind the red power wire as the one for safe disconnect.
JohnGC
Active member
Hi Poey,
In this Nordkyn article ;
http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/
Is the following;
A sales manager at Sinopoly I was talking to was adamant about using 100Ah or 200Ah cells only for assembling marine battery banks, with 100Ah being preferred and 200Ah acceptable. Large cells simply don’t have the structural strength-to-weight ratio required to be taken to sea on board small crafts and would exhibit shortened life due to internal mechanical damage arising from on-going vessel motion. It is common sense: as a cell becomes larger, its internal weight increases much faster than the rigidity and surface area of the casing and the casing is all what holds the plates together in a prismatic cell.
Since you used cells which are significantly higher capacity than 200Ah, I wonder if you have some other information that contradicts or mitigates this?
John
In this Nordkyn article ;
http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/
Is the following;
A sales manager at Sinopoly I was talking to was adamant about using 100Ah or 200Ah cells only for assembling marine battery banks, with 100Ah being preferred and 200Ah acceptable. Large cells simply don’t have the structural strength-to-weight ratio required to be taken to sea on board small crafts and would exhibit shortened life due to internal mechanical damage arising from on-going vessel motion. It is common sense: as a cell becomes larger, its internal weight increases much faster than the rigidity and surface area of the casing and the casing is all what holds the plates together in a prismatic cell.
Since you used cells which are significantly higher capacity than 200Ah, I wonder if you have some other information that contradicts or mitigates this?
John
Poey50
Well-known member
Thanks for raising this John. I'm aware of the concern being 70ah above this recommendation. As I've aged I've tended to favour data over adamant views or even appeals to common sense and although I've seen this debated, it seems a rather data-free area. I am aware of people using these cells or larger in both boats and off-road vehicles and these are some years ahead of me and have heard no adverse results. But it's a good thing to keep in mind.
Edit: have just checked some of the discussion on Lithium Batteries on a Boat Facebook group. 200s are very common but bigger cells are not unusual. Someone reported 400ah cells used without problem for 7 years. Larger are not unusual, the largest being by one of (apparently) the most knowledgeable members being 1000ah.
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JohnGC
Active member
I've haven't been able to find a definitive reference either. Nor have I found anyone claiming to have seen this type of damage on a boat battery.
Also, a battery low down near the water-line (and properly secured on a cruising sailing vessel) is unlikely to suffer as high an intensity of vibration or shock as its equivalent in a road vehicle. I'm thinking of pot-holes, bouncing up kerbs and the like. Although ramming the harbour wall might!
It strikes me that the compression housing might help mitigate potential shock damage. It would be relatively easy to fix the battery using anti-vibration mounts if room allowed and it was a real concern.
John
Poey50
Well-known member
I agree with your comments on the compression housing. Although the original quote mentions iñternal damage it links this to the integrity of the exterior cell wall so compression must help. I've also taken some trouble to ensure there's no movement in the battery box which itself is about 3/4 of the way back to the stern so not subject to slamming. As you say, off-roaders have it much worse.
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vas
Well-known member
and us moboes then, slamming at planning speed wont be kind to the batteries...
Poey50
Well-known member
Shouldn't be difficuit to add some damping but, aside from the Nordkyn quote, it's not something that seems to be considered a regular problem.
Mikedefieslife
Member
I don't see it as a problem. These cells aren't large. In fact smaller than the plastic cased ones. People have installed crazy sizes in the plastic cells, and haven't reported big problems as yet.
I often lambast the way my boat moves into the wind. In fact the force was so strong recently that I snapped a mast tang. Still the moment is much less than riding off road, and the vibrations a great deal less than riding on the road.
Time will tell, provided the cells are perfect to begin with. Let's say they only last 3000 cycles rather than 5000. Does that really matter? The actual spec sheets lists >6000 cycles 100% DOD. I'd take that with a pinch of salt though.
Poey50
Well-known member
Update:
Sea trials
This shows a two day weekend with first proper use of the LFP pack. I'd left it at 37% SOC from the previous weekend with all solar disconnected. At -2d (days) you can see the first small peak when solar outdid usage, then an overnight drop to around 30% SOC and repeated the following night. In the morning on a brief passage I used the engine for the first time giving the steep climb in SOC. Once it got to 53% SOC I switched off the external alternator regulator and carried on under engine without charging.
This may all seem unremarkable, but this was with full time use of the fridge (something I have never done before) and fairly heavy use of the diesel heater. I hadn't quite got my head round how much time I would be likely to spend around the mid-range of SOC and, how important it was to ensure that all charging sources can be switched off. This takes some getting used to after 20 years of trying not to go below about 30% discharged and trying to ensure that batteries could get back to 100% before next usage.
Short version - I love my LFP pack.
Sea trials
This shows a two day weekend with first proper use of the LFP pack. I'd left it at 37% SOC from the previous weekend with all solar disconnected. At -2d (days) you can see the first small peak when solar outdid usage, then an overnight drop to around 30% SOC and repeated the following night. In the morning on a brief passage I used the engine for the first time giving the steep climb in SOC. Once it got to 53% SOC I switched off the external alternator regulator and carried on under engine without charging.
This may all seem unremarkable, but this was with full time use of the fridge (something I have never done before) and fairly heavy use of the diesel heater. I hadn't quite got my head round how much time I would be likely to spend around the mid-range of SOC and, how important it was to ensure that all charging sources can be switched off. This takes some getting used to after 20 years of trying not to go below about 30% discharged and trying to ensure that batteries could get back to 100% before next usage.
Short version - I love my LFP pack.
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LoneHort
Member
Hi can I ask 2 question's here. I thought threadlock was an insulator and yet am I reading correctly that you used it to attach the stainless studs into the cells? 2nd question is where did you source the copper bar to make your custom busbars? Many thanks again and giving serious though to taking the lithium plunge here.The 30mm studs were then cemented into the cell terminals with Loctite 243. They were hand-tightened and then backed-off 1/4 turn. The Loctite stabilises the terminal to stud connection which is otherwise quite loose and seals against damp to help protect the meeting of stainless steel stud and aluminium terminal.
Next came top-balancing of all the cells. Although the cells all are delivered with very similar voltages the disparity only emerges near the top and bottom of the charge curve (the 'knees) and, without balancing one cell would reach full (and cut off the pack via the BMS) before the remainder are charged.
There are several guides to top balancing and a number of different theories about the maximum voltage for top-balancing and whether it should be done in stages or whether it needs to be done at all. In the end I downloaded the guide from this page (top right) and found it reliable. Failures at top balancing are very costly with people reporting terminally bloated cells, usually because they got impatient and turned up the voltage. It goes very slowly and then very fast and catches people out. As long as you NEVER touch the voltage setting once the supply unit is connected you can trust it.
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
I used the same power supply unit from Amazon which I found had a very good professional review despite the relatively low cost.
Following the directions above, I first put the pack into it's proper 4S 12 volt arrangement and charged it until one cell first hit 3.65 volts whereupon I was pleased to see the BMS automatically disconnect the charger. Without that first stage, simply putting them all in parallel and charging at low amps takes many days.
So the next stage was arranging them in parallel following the instructions exactly to have the power supply deliver no more than 3.65 volts measured at the end of the leads prior to being connected to the battery.
I checked alll voltages every 15 minutes for ten hours (with a break for a sleep in the middle) because of the horror stories of leaving cells during this time. I needn't have worried - all were balanced and I finished the exercise when they was no more than 0.001 volt difference between the calls and charging at 0.11 amps. There was never any danger of overcharging.
Poey50
Well-known member
Yes, thread lock is an insulator of sorts. But the stainless steel stud to cell terminal connection only functions to hold the bus bar (and other connectors) to the terminal - it doesn't itself need to contribute to the the connection. This is just as well as stainless steel is 41 times more resistive than copper.
I got my copper strip from Ebay, if I recall correctly. It isn't hard to find. In the end I was able to use most of the nickel plated busbars supplied with the cells as the extra insulation added between cells was only 0.5mm.
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Poey50
Well-known member
Update: some post-installation thoughts on a weakness in my system.
For those following, you may remember that I am using a 4 stage monitoring and control system which escalates from occasional monitoring to catastrophic-level protection. To recap:
1. Occasional Bluetooth monitoring of state of charge, individual cell voltage, cell temperature, balance between cells and state of charge history via the 123SmartBMS Bluetooth app. (This is where the phone screen-shots I have been putting up come from.)
2. Alternator, mains and solar charging set to autonomously end when absorption voltage is reached (13.8v for alternator, 14.0v for solar). Alarm in 3 will sound if these figures are exceeded. In addition the external regulator has an additional automatic voltage disconnect at 14 volts in case the external regulator fails.
3. Monitoring and alarms for pack high voltage, low voltage, high temperature and low temperature using the relay of the Victron BMV712 plus external alarm siren. The BMV also gives another Coulomb counting display for state of charge. The parameters are slightly outside the voltage cut-off of the chargers and slightly inside the parameters for the BMS disconnects below.
4. BMS and relay high voltage disconnect of charge bus, low voltage disconnect of load bus, high temperature and low temperature disconnect. All of these are based on cell readings rather than pack reading. This is catastrophic-level protection designed to protect the cells but not leave me high and dry. If the charging is disconnected the loads are unaffected and vice versa. (There is also a Sterling Alternator Protect fitted to prevent an alternator fry-up in the unlikely case of a high voltage disconnect during alternator charging.)
The sharp eyed will have noticed that levels 2 and 3 depend entirely on the system responding to pack voltage. Only 1 and 4 are using individual cell data and this is where the weakness lies. Both the alarms and the autonomous chargers depend on the end of absorption voltage being safe for the LFP cells. So for an end voltage of 13.8 volts this is equivalent to 3.45 volts per cell - very safe and able to give a full charge. But if the cells voltages were as follows: cell one 3.3v, cell two 3.3v, cell three 3.3v, and cell four 3.8v then the pack voltage would be 13.7 volts and this would fail to trigger the alarm and the fail to stop the charger(s) which could damage cell four - any voltage over 3.65 volts being problematic. Of course the high voltage cut-off at level 4 would prevent this but I don't want to solely depend on that.
So long story, short ... the use of absorption voltage to trigger alarms and end charging is only functional when the cells are reasonably in balance. Therefore, some occasional monitoring of cells at level 1 is necessary to ensure this and some occasional full charge to allow the passive balancing of the BMS to work is also a good idea. More sophisticated BMSs are able to end charging and to sound alarms at individual cell level and this is the ultimate in a fully automatic system. Such BMSs also cost more and, it might be argued, there is less redundancy should the BMS fail.
Anyway, something to be aware of if you are considering this kind of system.
For those following, you may remember that I am using a 4 stage monitoring and control system which escalates from occasional monitoring to catastrophic-level protection. To recap:
1. Occasional Bluetooth monitoring of state of charge, individual cell voltage, cell temperature, balance between cells and state of charge history via the 123SmartBMS Bluetooth app. (This is where the phone screen-shots I have been putting up come from.)
2. Alternator, mains and solar charging set to autonomously end when absorption voltage is reached (13.8v for alternator, 14.0v for solar). Alarm in 3 will sound if these figures are exceeded. In addition the external regulator has an additional automatic voltage disconnect at 14 volts in case the external regulator fails.
3. Monitoring and alarms for pack high voltage, low voltage, high temperature and low temperature using the relay of the Victron BMV712 plus external alarm siren. The BMV also gives another Coulomb counting display for state of charge. The parameters are slightly outside the voltage cut-off of the chargers and slightly inside the parameters for the BMS disconnects below.
4. BMS and relay high voltage disconnect of charge bus, low voltage disconnect of load bus, high temperature and low temperature disconnect. All of these are based on cell readings rather than pack reading. This is catastrophic-level protection designed to protect the cells but not leave me high and dry. If the charging is disconnected the loads are unaffected and vice versa. (There is also a Sterling Alternator Protect fitted to prevent an alternator fry-up in the unlikely case of a high voltage disconnect during alternator charging.)
The sharp eyed will have noticed that levels 2 and 3 depend entirely on the system responding to pack voltage. Only 1 and 4 are using individual cell data and this is where the weakness lies. Both the alarms and the autonomous chargers depend on the end of absorption voltage being safe for the LFP cells. So for an end voltage of 13.8 volts this is equivalent to 3.45 volts per cell - very safe and able to give a full charge. But if the cells voltages were as follows: cell one 3.3v, cell two 3.3v, cell three 3.3v, and cell four 3.8v then the pack voltage would be 13.7 volts and this would fail to trigger the alarm and the fail to stop the charger(s) which could damage cell four - any voltage over 3.65 volts being problematic. Of course the high voltage cut-off at level 4 would prevent this but I don't want to solely depend on that.
So long story, short ... the use of absorption voltage to trigger alarms and end charging is only functional when the cells are reasonably in balance. Therefore, some occasional monitoring of cells at level 1 is necessary to ensure this and some occasional full charge to allow the passive balancing of the BMS to work is also a good idea. More sophisticated BMSs are able to end charging and to sound alarms at individual cell level and this is the ultimate in a fully automatic system. Such BMSs also cost more and, it might be argued, there is less redundancy should the BMS fail.
Anyway, something to be aware of if you are considering this kind of system.
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Zing
Well-known member
I think this is fine. You are over-fretting. The cells won't go out of whack and you won't have the problems you are concerned about and if you do, it will be so briefly no damage will be done. Personally I would set the voltage levels so the battery runs at say 85% charge down to 15% charge. It will give a much longer life for little inconvenience or disadvantage. I don't bother with temp monitoring as I never go cold and if it will go hot then the overvoltage will trigger first.
yoda
Well-known member
Update:
Sea trials
This shows a two day weekend with first proper use of the LFP pack. I'd left it at 37% SOC from the previous weekend with all solar disconnected. At -2d (days) you can see the first small peak when solar outdid usage, then an overnight drop to around 30% SOC and repeated the following night. In the morning on a brief passage I used the engine for the first time giving the steep climb in SOC. Once it got to 53% SOC I switched off the external alternator regulator and carried on under engine without charging.
This may all seem unremarkable, but this was with full time use of the fridge (something I have never done before) and fairly heavy use of the diesel heater. I hadn't quite got my head round how much time I would be likely to spend around the mid-range of SOC and, how important it was to ensure that all charging sources can be switched off. This takes some getting used to after 20 years of trying not to go below about 30% discharged and trying to ensure that batteries could get back to 100% before next usage.
Short version - I love my LFP pack.
While I understand you are in the early stages of use for your pack I am a little bemused. If you are going to only charge to something around 50% capacity of your pack your available energy is only 50% of the maximum. Are you saying you designed a pack that has twice the required capacity in order not to need charging close to full capacity?
Yoda
Poey50
Well-known member
Zero fretting here. Strength comes from a clear-eyed evaluation of potential weaknesses.
Poey50
Well-known member
This has come up before. I can stay around mid-range for weekend and holiday use. I also have the option of charging fully for the longer offshore passages and cruising I eventually have in mind. LFP gives choices that are impossible with lead acid.
