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

[exMaggieDrum]

Looking at the House Power BMS site, the units are obviously intended for EV use but they are being put in boats too. I see they recommend the use of an AC Solid State Relay to cut power to a charger via a HVC from the BMS board. They offer a 40A version with an optional (recommended) heat sink for $28. This may be a good solution for cutting the charger output of my inverter/charger by cutting the input AC to it rather than cutting the DC output, which is what I was thinking before. Has anyone done so or considered it and are there potential problems in doing so? There would be some loss of AC power to heat but I would think it is very minor??

There are others available.

I can also set a high voltage cutout with my inverter/charger charge function so the SSR would be a failsafe, but it would address the issue from the AC side rather than the DC side.

[mbartosch]

Originally Posted by exMaggieDrum

Couple of quick questions:
- where did you buy your cells?
- how did you turn off the alternator field(s) - at the BMS warning time or the cutout, or??

I live in Germany, hence I bought them at a local dealer (LiTrade Shop | Akkus und Zubehör für Elektroautos). I took the cells home and top-balanced them manually.

I ordered the cells "pre-balanced" which means that the vendor connected my cells in parallel and charged them to 3.6 V just prior to shipping. When they arrived, I temporarily arranged them in their final 4P4S configuration, labeled them so I could reproduce this and discharged the pack a bit (a few percent) using a 4 Ohm 50 W resistor.
I temporarily rigged the BMS and an improvised HVC relay to be safe (and test the BMS). Then I used a lab power supply to bring the pack to 14.4 V (3.6 V cell voltage) again.
I monitored the entire charging process thoroughly and watched cell voltage closely. The blinking cell module indicators helped identify the "top charged" cells. I then used a 1 Ohm 25 W resistor to bridge the one cell pack that was edging on the top for about 5 - 10 seconds. Repeated this until all cell packs showed the same voltage.
Once the pack was top balanced with this method, I discharged the pack to 60 %, disassembled and stowed them for transport to the boat. There I reassembled the pack and installed them physically.

The whole process has been described in this thread several times and I just repeated what I learned here. Thanks to all who shared their knowledge!

The alternator is a Balmar 6 type with an external Balmar MC 614 regulator. The MC 614 provides a "Ignition" input. It only supplies field to the alternator if the "Ignition" input carries +12 V. In my setup this input is wired to the ignition circuit and is disabled by the HVC relay controlled by the BMS.

My setup does not have a "warning only" stage. I rely on my charging sources being configured correctly, providing 13.8 (14.0 for solar, they don't have voltage sense) to the batteries. You cannot overcharge the pack that way if everything works fine. The HVC is only a safety measure if something goes wrong with the charging sources, so no warning level is needed.

Regarding LVC I have configured my battery monitors to start beeping when reaching 20 % SoC, so I have plenty of time to react before things go whacky.

[mbartosch]

Originally Posted by exMaggieDrum

Looking at the House Power BMS site, the units are obviously intended for EV use but they are being put in boats too. I see they recommend the use of an AC Solid State Relay to cut power to a charger via a HVC from the BMS board. They offer a 40A version with an optional (recommended) heat sink for $28. This may be a good solution for cutting the charger output of my inverter/charger by cutting the input AC to it rather than cutting the DC output, which is what I was thinking before. Has anyone done so or considered it and are there potential problems in doing so? There would be some loss of AC power to heat but I would think it is very minor??

I am using a electromechanical 2 pole relay (Etalko) for HVC cutoff on the AC side of the charger/inverter. It normally connects L and N from the shore side RCD to the charger. If the relay is activated, it cuts both L and N and thus stops charging.
You can also cut the DC side, but AC is easier (smaller components and less complicated wiring).
However, when dealing with AC voltage remember that mistakes can be deadly. Make sure you know what you are doing or involve an electrician. Really.

I can also set a high voltage cutout with my inverter/charger charge function so the SSR would be a failsafe, but it would address the issue from the AC side rather than the DC side.

This is also an option if you charger supports it, but that was not available in my Multiplus version. It avoids dealing with AC circuitry which may be sensible if you are not a professional.

[mbartosch]

Originally Posted by stefano_ita

Just to know, wich alternator regulator do you use for charging 12 or 24 v lithium battery pack? I really can't find it Help plz

The Balmar MC 614 is praised by Maine Sail and has been highly recommended by several other forum members - so I chose this. I am very happy with this device (although programming it sucks...).

[Highland Fling]

Where to start.

Well I have 800AH 16 200A Winston TS cells

200AH are sitting in a 4P configuration doing nothing.

The House bank is 3 times 200AH in a 4S configuration
200AH is sperately switched and 'tends to be' 'SPARE CAPACITY'

400AH 2 X 4S batteries are connected in paralel and are 'our normal working house bank'.

We still have one 8D AGM which is now the engine start battery. it is independently swiched can be connected to the house bank as well and all batteries are charged VIA a Diode blocking device.......this drops the 14+ volts from the DR 10SI 60A alternator down to a nice 13.8 volts or so.

I am NO LONGER HYPER about my batteries.

We charge them using solar.....Blue Sky Solar boost 2000 tweaked by me to automatically stop charging at 13.8V. It took days to get the batteies up to that 13.8V so I could adjust the BSSB2K controllers to trip off.

We are using an Austrailain BMS (see my pictures) with inbuilt relay and manually opearted override switch which is rated for 200A which is why we have our batteries in this configuration.

We also have the same companies cell boards and use a RC battery monitoring device......

Typically my cell imbalance is 0.001 of a volt when I am bored and want to look at it. This is after one yaer of operation including six months laid up on the hard with no charging or discharging. Typically my house bank is at 13.2 V sometimes 13.6V so we are not stressing these batteries at all not even when we are driving the 2KW inverter hard when we cook. Just now at nearly 20:00 hours with the F/F running (my biggest normal daily load) (apart from the inverter when we cook electrically now) I am 50AH down and voltage is 13.15V

[senormechanico]

Originally Posted by exMaggieDrum

Looking at the House Power BMS site, the units are obviously intended for EV use but they are being put in boats too. I see they recommend the use of an AC Solid State Relay to cut power to a charger via a HVC from the BMS board. They offer a 40A version with an optional (recommended) heat sink for $28. This may be a good solution for cutting the charger output of my inverter/charger by cutting the input AC to it rather than cutting the DC output, which is what I was thinking before. Has anyone done so or considered it and are there potential problems in doing so? There would be some loss of AC power to heat but I would think it is very minor??

There are others available.

I can also set a high voltage cutout with my inverter/charger charge function so the SSR would be a failsafe, but it would address the issue from the AC side rather than the DC side.

I have done the HVC cutout to the shore charger with a SS switch.
I mounted the switch on a hunk of aluminum.
I rarely use the charger a Xantrex 20 amp thing, and even if it goes to bulk, the aluminum never feels warm.
Maybe I just am cheap and like to live on the edge, but I have neither HVC nor LVC main DC relays.
The boat's at the dock in our backyard, so I can check on it anytime I feel like it.
My BlueSky controller with IPN remote will show me (among other things) max and min voltages since I last reset it as well as aH in and out. Voltage rarely goes over 13.8 occasionally to 13.9, and never below 12.3 while using the inverter to heat the hot water tank. That takes about a hundred amps for a half hour from our single 200aH bank. I feel comfortable with that.

[Jd1]

Originally Posted by mbartosch

The Balmar MC 614 is praised by Maine Sail and has been highly recommended by several other forum members - so I chose this. I am very happy with this device (although programming it sucks...).

They couldn't have made it more convoluted and painful if they tried

BTW, remember to keep the MC 614 in a cool spot - the engine compartment is NOT a recommended place !!!

[mcarling]

Originally Posted by Highland Fling

400AH 2 X 4S batteries are connected in paralel and are 'our normal working house bank'.

We still have one 8D AGM which is now the engine start battery. it is independently swiched can be connected to the house bank as well and all batteries are charged VIA a Diode blocking device.......this drops the 14+ volts from the DR 10SI 60A alternator down to a nice 13.8 volts or so.

I recommend against ever connecting LiFePO4 batteries in parallel with any type of lead-acid batteries.

[Jd1]

Originally Posted by mcarling

I recommend against ever connecting LiFePO4 batteries in parallel with any type of lead-acid batteries.

Why ?
I have a lead acid house bank and a single spare lead acid emergency battery hooked up in parallel with a LiFEPo4 house battery bank and have had zero issues. The batteries are all isolated from each other, I have separate battery state-of-charge monitors for both house banks and I don't have to worry about shutting down the alternator when I disconnect the fully charged lithium bank from the charge system. The lead acid batteries are connected to the charge bus all the time.
The only down side is that the alternator is set up for a lead acid charging profile which is less than optimal for charging the lithium bank.
I am thinking of trying putting a diode (or maybe even two) in series with the charging bus to the lead acid batteries so I can bring the alternator voltage up a bit for faster charging of the lithium bank. I haven't fully thought through all the implications of doing this yet so comments from people who have done this are welcome.

[mcarling]

Originally Posted by Jd1

I have a lead acid house bank and a single spare lead acid emergency battery hooked up in parallel with a LiFEPo4 house battery bank and have had zero issues. The batteries are all isolated from each other, I have separate battery state-of-charge monitors for both house banks and I don't have to worry about shutting down the alternator when I disconnect the fully charged lithium bank from the charge system. The lead acid batteries are connected to the charge bus all the time.

If you have the batteries isolated from each other then they are not connected to each other in parallel. Either they are connected or they are isolated. Either current can flow between the batteries (in one or both directions) or current cannot flow between the batteries.

Originally Posted by Jd1

Why ?

The short answer is that they have incompatible voltages. One of the consequences is that if they are both fully charged and connected to each other, the lead-acid batteries (if they have enough capacity) will keep the LiFePO4 batteries above 3.4V per cell, which is likely to degrade their service life. How severe that effect would be depends on the relative capacity of the two banks. You hit on a similar issue below with charging profiles, which are completely incompatible (if one wants batteries to enjoy a normal service life).

Originally Posted by Jd1

The only down side is that the alternator is set up for a lead acid charging profile which is less than optimal for charging the lithium bank.
I am thinking of trying putting a diode (or maybe even two) in series with the charging bus to the lead acid batteries so I can bring the alternator voltage up a bit for faster charging of the lithium bank. I haven't fully thought through all the implications of doing this yet so comments from people who have done this are welcome.

[Maine Sail]

Originally Posted by mcarling

The short answer is that they have incompatible voltages. One of the consequences is that if they are both fully charged and connected to each other, the lead-acid batteries (if they have enough capacity) will keep the LiFePO4 batteries above 3.4V per cell, which is likely to degrade their service life. How severe that effect would be depends on the relative capacity of the two banks. You hit on a similar issue below with charging profiles, which are completely incompatible (if one wants batteries to enjoy a normal service life).

One other problem with both lead and LFP banks in parallel is that when not charging the resting OCV of LFP, about 13.2V - 13.3V, is a continual float voltage for lead and thus the lead bank will continually bleed current from the LFP battery.

This bleed rate usually far exceeds using a BMS for HVC & LVC. Cutting the red power wire to an MC-614 & dropping a solar reg etc. in an HVC is really not that difficult I am using a couple of Cole-Hersee 70A relays that cost about $6.00......

[Maine Sail]

Originally Posted by Jd1

They couldn't have made it more convoluted and painful if they tried

BTW, remember to keep the MC 614 in a cool spot - the engine compartment is NOT a recommended place !!!

Yes if you don't program Balmar regs regularly they can be a PITA to get used to. Once you've done it a few times it becomes very easy. To drop voltage limits to LFP levels you start by reducing the float voltage first. I essentially use float as an "OFF" voltage by setting it below LFP resting voltage. The reason for setting float first is because Bulk 1 (a trigger voltage) and absorption can't be lower than float.

[Highland Fling]

Originally Posted by Jd1

Why ?
The only down side is that the alternator is set up for a lead acid charging profile which is less than optimal for charging the lithium bank.
I am thinking of trying putting a diode (or maybe even two) in series with the charging bus to the lead acid batteries so I can bring the alternator voltage up a bit for faster charging of the lithium bank. I haven't fully thought through all the implications of doing this yet so comments from people who have done this are welcome.

I have my alternator feeding the diode block and as yet have not taken the diode to the LIFePO4 batteries out of circuit. and wired the alternator direct to the LIFePo4 house bank

MY LIFePO4 house bank seem totally happy with this situation and set up.

I have a KISS set up and don't see a NEED in my case at least for a more complicated set up which spilts charging and discharging circuits.

Tis easy to overthink this and have all sorts of safeguards that we never had with LA batteries......

MY BMS and the cell boards will handle any HVC (UNLIKELY) situations and the equally unlikley situation of a LVC.

In the event of one of these situations happening I could quickly switch in the 8D AGM battery without any issues as the BMS's would have taken the LIFePO4 batteries out of circuit.

I see all of these siutations as theoretically possible but highly unlikely. BUT then I have a DIY install that meets my needs and others are doing this 'professionally' so different 'rules' apply to their installations.

[Jd1]

Originally Posted by Highland Fling

I have my alternator feeding the diode block and as yet have not taken the diode to the LIFePO4 batteries out of circuit. and wired the alternator direct to the LIFePo4 house bank

<snip>

MY BMS and the cell boards will handle any HVC (UNLIKELY) situations and the equally unlikley situation of a LVC.

In the event of one of these situations happening I could quickly switch in the 8D AGM battery without any issues as the BMS's would have taken the LIFePO4 batteries out of circuit.

Just keep in mind that if your BMS disconnects the LIFePO4 bank and you do not have a regular battery connected, you HAVE to insure the BMS disconnects the alternator field or else you will likely pop the alternator.

[exMaggieDrum]

Originally Posted by Maine Sail

One other problem with both lead and LFP banks in parallel is that when not charging the resting OCV of LFP, about 13.2V - 13.3V, is a continual float voltage for lead and thus the lead bank will continually bleed current from the LFP battery.

This bleed rate usually far exceeds using a BMS for HVC & LVC. Cutting the red power wire to an MC-614 & dropping a solar reg etc. in an HVC is really not that difficult I am using a couple of Cole-Hersee 70A relays that cost about $6.00......

I was planning on using a Xantrex Echo-Charger to keep my start battery charged. It has a 13.0v (nominal) cut-in setting so it would act as a drain as you state here. I can easily put a relay on the input lead from the house battery so that the circuit would be turned off. Thanks for the heads up on this. Spot on as usual.