Inverter Wiring & Sparks

[Stormy98]

I'm in the planning and testing stage for an electrical upgrade to LiFePo. I'm considering replacing the old Xantrex inverter/charger with a transfer switch and a Renogy inverter that I have on hand.

When testing the inverter with a direct connection to the battery, there's a big spark when the initial connection is made. I understand the reasons why and how it can be avoided by using a resistor prior to connecting the battery.

My question is this: will this spark occur internally in the transfer switch when it switches from shore power to the inverter? Or in the cutoff switch I'm planning on installing between the battery and the system? If so, is there something I can do to keep the capacitors charged in the inverter?

[Scalf77]

As long as the battery is connected to inverter (Caps) they will remain charged. If you have an inrush current issue with inverter and LiFePo battery then a pre-charge would be needed. So your cutoff switch would be the area of concern.

When you got the "spark" was it when you connected to the LiFePo battery? If so did the BMS report any errors?

What Xantrex inverter/charger do you have?

[Stormy98]

The existing inverter/charger is a Trace M1512 (Trace became Xantrex). Nothing wrong with it other except my understanding is the old tech won't fully charge LiFePo batteries.

Yes, for my test I directly connected the inverter to the battery. The BMS of the battery doesn't have a way of being externally monitored.

Makes sense that the cutoff switch will always be a potential source of a spark. I realized I wasn't thinking about the transfer switch properly - obviously it will switch the output of the inverter, not the input. So that shouldn't be an issue as the battery will remain connected to the inverter even when shore power is connected.

[boywonder]

Originally Posted by Stormy98

The existing inverter/charger is a Trace M1512 (Trace became Xantrex). Nothing wrong with it other except my understanding is the old tech won't fully charge LiFePo batteries.

AGM settings can be very close or fine for LiFePo4.....

Do you have many choices for bulk, absorb and Float?

[Stormy98]

Unfortunately, no. The manual states:

The microprocessor has parameters for charging liquid electrolyte or gel cell batteries. The factory setting is for the typical liquid electrolyte battery.

And:

• Bulk Voltage- This is the maximum voltage at which the batteries will be charged during a normal charging cycle. The normal range is 2.367 to 2.4 volts per cell. For a 12 VDC battery (6 cells) this is 14.2 to 14.4. Liquid electrolyte batteries are usually set to the higher voltage, while gel cell batteries are set to the lower.

• Float Voltage- This is the voltage at which the batteries will be maintained after they have been charged. A range of 13.2 - 13.4 is appropriate for most sealed and non-sealed batteries.

• Absorption Stage- During this part of the charge cycle, the batteries are held at the bulk voltage and accept whatever current is required to maintain this voltage.

The method for selecting battery type is simply a jumper. No other controls. So it seems for the gel setting the bulk/absorption voltage is 14.2 and the float voltage is 13.2.

Would either setting (electrolyte or gel) be acceptable for LiFePo?

[boywonder]

Originally Posted by Stormy98

Unfortunately, no. The manual states:

The microprocessor has parameters for charging liquid electrolyte or gel cell batteries. The factory setting is for the typical liquid electrolyte battery.

And:

• Bulk Voltage- This is the maximum voltage at which the batteries will be charged during a normal charging cycle. The normal range is 2.367 to 2.4 volts per cell. For a 12 VDC battery (6 cells) this is 14.2 to 14.4. Liquid electrolyte batteries are usually set to the higher voltage, while gel cell batteries are set to the lower.

• Float Voltage- This is the voltage at which the batteries will be maintained after they have been charged. A range of 13.2 - 13.4 is appropriate for most sealed and non-sealed batteries.

• Absorption Stage- During this part of the charge cycle, the batteries are held at the bulk voltage and accept whatever current is required to maintain this voltage.

The method for selecting battery type is simply a jumper. No other controls. So it seems for the gel setting the bulk/absorption voltage is 14.2 and the float voltage is 13.2.

Would either setting (electrolyte or gel) be acceptable for LiFePo?

14.2-14.4 for absorb is fine..that's 3.55-3.6V per cell....the upper limit is 3.65V/cell for LiFePo4.


..and float at 13.4 is also fine..both of these are pretty much what most of us are running for LiFeP04.


There are two other things to think about, I think LiFeP04 likes a longer absorb time than typical lead acid or use a "tail current" method....this may be relatively minor.......I'm sure Scalf77 can shed more light here.

The other much more important parameter is equalization......I'm pretty sure gel profiles don't have this mode since they are sealed, but a flooded battery setting may use equalization. You don't want equalization with LiFePo4's since they are also sealed and don't need it.

If you can set bulk/absorb voltage at 14.2-14.4V and float around 13.4 without equalization (gel mode) you should be fine.

[Stormy98]

Thank you. There’s nothing in the manual about equalization or tail current. There is this though:

The BAT SIZE A/H control is used to inform the inverter's microprocessor of the battery bank size. This allows the inverter to make better “over-discharge protection” and battery charging decisions. Battery bank size is adjustable from 50 to 1000 amp hrs.

The control is a dial with minimal markings so I’ll attempt to set it to 200 (I have two batteries).

Unless there’s a chance of damaging the new batteries, I’ll give it a go with the existing inverter/charger. I now have a battery monitor so I’ll be able to check the voltages with both settings. Appreciate the info.

[boywonder]

Equalization can damage sealed batteries (AGMs and LiFeP04's are sealed..and I thought gels are too but that's clear to me..never used one)


Equalization is a cycle that runs every so often to basically "overcharge" the battery a little to warm up/stir up the electrolyte in flooded lead acid batteries to prevent sedementation.


Equalizing LiFeP04s (and AGMs) can cause them to vent if overheated too much.....shortening the life of the battery significantly...

[boywonder]

I did some googling.....


Is this chart in your owner's manual?




...notice the sealed/gel profile settings don't equalize........that should work fine.

...however.....absorb is 14.1 and float is 13.5......won't hurt the battery but the absorb is a little lower than ideal....


Also, as kinda expected...float mode is set at 1 hour.......

[Scalf77]

So Trace was pretty good at the time, but that time has passed. The Xantrex Prosine has very good programmability, which is why I asked. Not sure I would think about using the Trace on LiFePo4 batteries.

Your battery manufacturer should have the charge settings. I would make sure that my charger falls within those parameters.

Generally the time for absorption is much shorter for lithium batteries than what you would use for lead. Batter for lithium that you have a charger that you can set the absorption time directly.

If it was me I would upgrade.