LiFePo4 battery setup questions

[roetter]

Originally Posted by ebaugh

I looked at your diagram and see no major issues. You may suffer the same problem I do, my start batteries never get fully charged since the rest of the entire charging system is set to LFP voltages. Your isolators may accentuate this since the start battery is not "floated" by the LFP bank and will slowly self discharge between engine runs and then probably never get back to full charge. Consider moving the start batteries in front of the isolator to gain 1/2 volt or so for them.

Thanks for the info. The Cristec isolators should not have a voltage drop. I don't know what is inside to achieve the separation and no voltage loss. However, I plan to check on the starter batteries and i stall a battery-to-battery charger if there is a problem.

[roetter]

dlentz - after reading your reply I went thinking and searching again. Thanks for that push.

I found a programmable Battery Voltage Guard. It has programmable over and under voltage set points that trigger one relay each. Both voltages can be set with a hysteresis. That means for example trigger over voltage at 14.5V and "un-trigger" at 14.2V. This prevents switching on and off all the time. Both set points can also be programmed with a delay. You may not want to cut your charging sources because a large house load caused a slow charger reaction to cause a short spike of over voltage.

This is what I am pondering now.
I want to use the guard as my "charge controller" controlling ALL charge sources - shore, alternator, solar.
- Program the guard to trigger an over voltage at 14.5V (to be tested in real life)
- Program also a time delay of about 1 minute.
- "un-trigger" at 13.0V (to be tested in real life)
- Use this guard signal to trigger several relays that cut all charging (see diagram). This means I would have a relay each to cut the power to the:
- AC power to the shore power charger
- fileds of the two alternators
- Outback chargers from the solar panels

All charging will be interrupted by one signal. This would make for a very simple charge controller.

I would use the under voltage in the guard in a similar way, but to switch the LV - cut-off relay.

What do you guys think?

[roetter]

Here is the data sheet for the Battery Voltage Guard BW500.

[ebaugh]

I prefer a "fail safe" arrangement where without power the LFP bank is isolated. Not probably essential for an overcharge protector.

Your over charge voltage setting looked high?

Does this replace the CellLogs? I really believe cell level monitoring is necessary in a complete design. Both for safety, but probably even more so to save the bank if it becomes unbalanced. It depends on your perspective on insurance to cover unlikely scenarios.

[goboatingnow]

Originally Posted by roetter

Thanks for the info. The Cristec isolators should not have a voltage drop. I don't know what is inside to achieve the separation and no voltage loss. .......

mosfets configured to act as ideal diodes, generally

Dave

[roetter]

Originally Posted by ebaugh

I prefer a "fail safe" arrangement where without power the LFP bank is isolated. Not probably essential for an overcharge protector.

Your over charge voltage setting looked high?

Does this replace the CellLogs? I really believe cell level monitoring is necessary in a complete design. Both for safety, but probably even more so to save the bank if it becomes unbalanced. It depends on your perspective on insurance to cover unlikely scenarios.

I plan to keep at least one Celllog for monitoring and audible alarms. Will have it alarm on HV, LV, and differential voltage.

[darylat8750]

This is a great thread on a practical level. Keep going guys!

[T1 Terry]

When using the Junsi cell loggers as a safety back up, set the cell voltage to trigger an alarm at 3.6v HVC and 2.8v LVC, stay inside these limits and the cells will not be damaged. The higher you set the charging voltage the faster the battery will reach 100% SOC but the more you will be relying on the Cell Logger to protect the cells from damage. If you are sensible about the recharge periods the low cell alarm will never be activated, you have used every scrap of stored capacity out of the battery before a cell voltage of 2.8v is reached and you will be very close if not below 12v at the battery terminals.
Getting the feel for the flat charging and discharging curves is the biggest hurdle to over come, people are so conditioned to seeing the charge and discharge curves with lead acid batteries the first response is, something is wrong, the batteries aren't charging because the voltage isn't going up, and it doesn't unless the battery was completely discharged or until the battery is almost fully charged.

T1 Terry

[T1 Terry]

One other thing, I wish you good luck with trying to get an MPPT controller to work with any other charging source. If you can set the float voltage, set it to 13.8v, otherwise it will wait till the battery is virtually completely flat before it will drop back into boost mode as these things are set up for lead acid voltages, not lithium flat curve voltages.

T1 Terry

[poiu]

Originally Posted by roetter

Here is the data sheet for the Battery Voltage Guard BW500.

I am also in the middle of this process as my Trojans have gone belly up. Thanks a lot to all who have posted info on this subject, it has been very helpful.

My plan is almost the same as what is discussed here, though I haven't bought anything else yet apart from the batteries. They are in transit (8 x 700ah Winstons). I was going to go with this unit to protect from overcharge by using a secondary relay to cut the power to the 230v chargers and the alternator field. It could work as a charge controller also:

Programmable 4 Digit Red LED AC/DC Volt Meter with dual control. Good for HHO System

I think the unit you mentioned may be better. Where do you get them and what do they cost? No display, but Power draw is lower and that is attractive, otherwise they seem to do a similar job. Does the Junsi give an output at a low pack voltage level as well as at a high? It looks too sort of toy like to be doing such a responsible job? It seems a good idea to have one if for no other reason than to monitor voltage imbalance.

I also have one of these installed:

Magnetronic

It will give a relay output on an amp counter setting. I am not sure if that is the best way to protect on the low side and was going to test things first: I thought if the battery was at a fairly low state of charge and I used the bowthruster there might be such a voltage drop that with a voltage protection device the unit will pull the plug on me not at the best time. If I had the protection based on the amp counter it would avoid the involuntary disconnect. If the voltage drop is not below the minimum battery voltage in such a situation I could use it as my protection or possibly even have a second protection device set at a minimum level (2.9v/cell say). Any thoughts on this?

There are other probably useful options including the VRDC-40A from atkinsonelectronics.com. They also do an automatic genset start, useful to someone I am sure.

Or the CR5395 from CRMagnetics seems ok.

I want to get a high amp capacity latching contactor too. Not sure which one yet. Gigavac, Albright both make them.

[ebaugh]

The Junsi will alarm and activate a single low power relay for any cell error high, low or cell imbalance. The levels are programmable.

If you monitor at the cells, the voltage will not drop enough to trip, even with a bow thruster. 150A budges my bank about .02V per cell.

You want to trip on voltage not an Ah count. Preferably high on the high cell and low on the low cell. But some are using bank voltage. Use the Ah meter as a guide to you for estimating the current SOC.

[roetter]

Originally Posted by T1 Terry

One other thing, I wish you good luck with trying to get an MPPT controller to work with any other charging source. If you can set the float voltage, set it to 13.8v, otherwise it will wait till the battery is virtually completely flat before it will drop back into boost mode as these things are set up for lead acid voltages, not lithium flat curve voltages.

T1 Terry

On my previous boat I programmed the Outback MPPT to 14.6 absorption AND the same for float for FLA batteries. Otherwise, it often went into float and never went back to absorption during the day. So I would miss a lot of potential amp hours going into the batteries. Setting it to 13.8 absorption and float makes sense for LFP.

[roetter]

Great idea to use individual cell level for HVC and LVC. For some reason it slipped my mind. The Junsi looks like a toy, but I have good hope that they will be quite reliable. Have to use two of the, though. One for high and one for low voltage cut off.

[roetter]

Originally Posted by poiu

I am also in the middle of this process as my Trojans have gone belly up. Thanks a lot to all who have posted info on this subject, it has been very helpful.

My plan is almost the same as what is discussed here, though I haven't bought anything else yet apart from the batteries. They are in transit (8 x 700ah Winstons). I was going to go with this unit to protect from overcharge by using a secondary relay to cut the power to the 230v chargers and the alternator field. It could work as a charge controller also:

Programmable 4 Digit Red LED AC/DC Volt Meter with dual control. Good for HHO System

I think the unit you mentioned may be better. Where do you get them and what do they cost? No display, but Power draw is lower and that is attractive, otherwise they seem to do a similar job. Does the Junsi give an output at a low pack voltage level as well as at a high? It looks too sort of toy like to be doing such a responsible job? It seems a good idea to have one if for no other reason than to monitor voltage imbalance.

I also have one of these installed:

Magnetronic

It will give a relay output on an amp counter setting. I am not sure if that is the best way to protect on the low side and was going to test things first: I thought if the battery was at a fairly low state of charge and I used the bowthruster there might be such a voltage drop that with a voltage protection device the unit will pull the plug on me not at the best time. If I had the protection based on the amp counter it would avoid the involuntary disconnect. If the voltage drop is not below the minimum battery voltage in such a situation I could use it as my protection or possibly even have a second protection device set at a minimum level (2.9v/cell say). Any thoughts on this?

There are other probably useful options including the VRDC-40A from atkinsonelectronics.com. They also do an automatic genset start, useful to someone I am sure.

Or the CR5395 from CRMagnetics seems ok.

I want to get a high amp capacity latching contactor too. Not sure which one yet. Gigavac, Albright both make them.

Thanks. These are great devices. I will look more into them.
I may use the Junsi for cell voltage cut offs and the Lightobject for battery cut offs. I would control the same set of relays with both devices. This way I get some redundancy.

[darylat8750]

"I would control the same set of relays with both devices. This way I get some redundancy."

If you used separate relays for each device you would have total redundancy instead of partial. I don't know how reliable the relays are but when something is rarely used in the marine environment they can get sticky......

Has anyone figured out the losses incured per cycle (or how ever it is measured) to program an amp counter?