48v system, inverter and charge controllers reading higher

[dudeinthewoods]

I've got a 48v LiFePo4 battery bank working fine.

At the moment the BMS (which is accurate) shows 46.3v

The inverter and SCC is showing 10v higher at 56.6v when I hit the breaker on the scc the inverter reads ~ the same as the battery.

I wouldn't care about the numbers but
1) I want to understand why
2) It stops the battery from charging early
3) the invert trips from over voltage


It's probably something simple. I've got the inverter, battery and SCC all coming together on a bus bar. Do I need to wire it differently?


Thanks!

 

[gnubie]

You are seeing 56V on the inverter and SCC? Unexpected voltage differences can come down to trying to supply too much current over a given gauge wire, but to achieve a 10 volt drop that wire is going to be glowing.

Could you draw up a diagram of how your system is actually wired (check, not from memory), including indicating the wire gauge and charging current?

 

[dudeinthewoods]

Sure I'll draw it up in a few.
Not a voltage drop The wire is overkill (and not hot)
I've got 0000 from the battery to the bus and 4awg to the inverter.

SCC comes in goes to bus
Battery goes to bus
Inverter goes to bus


When I cut the scc the inverter voltage drops and matches battery voltage.

 

[gnubie]

If the battery is fully charged and the inverter is off, it's possible that your SCC is not programmed correctly and is continually pulling the battery up to 56v. Check the SCC configuration, ie make sure it has appropriate voltages set and a charging routine suitable for lifepo4.

What make and model SCC do you have?

 

[dudeinthewoods]

I've got makeskyblue for the scc

Shouldn't 48v be fully charged quite a bit higher?
I'll confirm the profile right now.

Edit: battery isn't fully charged or at least I don't think so.

 

[John Frum]

At the moment the BMS (which is accurate) shows 46.3v

The inverter and SCC is showing 10v higher at 46.6v when I hit the breaker on the scc the inverter reads ~ the same as the battery.

46.6 - 46.3 = 0.3 volts.
I am confused.

 

[dudeinthewoods]

56.6 on the inverter scc. Thanks for cAtching that should make a lot more sense. Typing on mobile and fat fingers.

Edit: fixed original post thanks.

 

[John Frum]

56.6 on the inverter scc. Thanks for cAtching that should make a lot more sense. Typing on mobile and fat fingers.

Edit: fixed original post thanks.

On the pv side or the system side?

 

[dudeinthewoods]

On the pv side or the system side?

DC side. I've got 150v~ on the PV side.
With my PV breaker off it shows 46v DC then when I turn it on connecting the PV side in it jumps 10v on the DC side.

 

[dudeinthewoods]

Ok may have solved this but not sure why..

I just turned it on in this order
Battery
DC side SCC
PV side SCC

Now I just want to make sure my SCC settings are good.

Bulk 56
Float 56

Under V 40
Under V recovery 42

 

[dudeinthewoods]

Just jumped up again and tripped the inverter. I guess they're pushing out 56v and that's what the inverter is getting instead of the battery voltage?

 

[gnubie]

Float is too high and explains what you are seeing. Set the float voltage to 54v.

If your inverter is tripping at 56v you will have to lower your bulk voltage too.

 

[dudeinthewoods]

Float is too high and explains what you are seeing. Set the float voltage to 54v.

Awesome thanks. I'll drop that and see what happens. If you don't hear anything for 24h I'm in your debt and will report back.

 

[gnubie]

If you do come back check the voltages your makeskyblue is showing vs what is actually on it's terminals. I only just noticed you are using one of them. From experience I've seen them be up to .4v off so when you key in 14v for the float the unit will actually be targetting 14.4v. That makes a difference with battery charging and may also explain your inverter tripping.

You should also check that the makeskyblue is actually exiting bulk/absorption charging and falling back to float at all. I've seen them stay at absorption indefinitely, which isn't good for the lifepo4 unless you set absorption voltage to be float voltage.

 

[dudeinthewoods]

So....

Multimeter died yesterday leaving in 5 min to get another one.

More importantly I realized my battery that said 48v is actually 46.8v. I am in the same boat as this guy.

Sold a 46.8v battery as 48v

I found the battery on ebay & then went to their site. I called them & told them what I was looking for (48v LP4). ESL & I got a 46.8v battery.... I am not a fan of Tech direct club.

diysolarforum.com

So that's part of it. I am waiting on the cells I bought from China and one got lost in shipment. So I bought that "48v" to hold me over until a replacement cell arrives.

That's a big part. Unfortunately the MSB SCC let's me go to 48v at the lowest. I'm going to keep an eye on it and make sure it does turn that LiFePo4 in to a fireball.

Thanks man learned a bit from you today.

 

[Ampster]

When I hear enough stories of a nominal 41.6 battery (13 x3.2=41.6) being called a 48 v battery it tells me the head guy at Tech Direct is not being straightforward. Yet, I am sure if you asked him he would say the truth is all in the details.