Campervan Lifepo4 DC to DC charger settings

[Beanis]

Hi all,

I know this is not strickly a solar question, but it is about charging Lifepo4 batteries in a campervan via a DC to DC charger, and trying to get the best results for my setup and usage. I think you guys are experts so maybe you can help!

My cmapervan setup is this:
-A 4 Varicore cell 12v 105ah self build battery, with Daly 100amp 4s BMS with Bluetooth.
-Paired with a Sterling Power DC to DC charger that takes van battery output and sticks it into the Lifepo4 battery
( https://sterling-power.com/collections/battery-to-battery-chargers )

I have two questions, and the answer to the 1st probably relates to the 2nd:

1. Should I match my Sterling Power DC to DC charger settings to be exactly the same as the Daly BMS settings?

At the moment the Sterling is on its standard setting for Lifepo4, which is to charge at 14.4, then float at 13.8 (I attach the chart for this, as not sure what condition is, that's 13.8 too)

My Daly BMS is set to charge until each cell voltage reaches 3.45 (see question 2 for why i sett his quite low). I have top balanced the cells before putting any of this in the van. The balance charge is set to come on at 3.37, and whenever the cells are different by 0.02v.

If the Daly is cutting off at a lower current than the Sterling, will the Sterling ever go into float anyway? I don’t want them conflicting, but also, not sure if setting the Sterling at 13.8 charge might make it charge slower? I heave heard float is not good, but surely the Daly just cuts any charge anyway, so how can it float?

2. I have heard that life span of batteries is decreased when fully charged all the time. Is this true? If so, considering I use my camper van a lot for general transport, but actually don’t use the leisure battery very often (maybe 1 weekend trip a month on average, so I won't be discharging it very often. And besides, if I do drive it and use the battery one night, I usually drive a bit the next day, so it will always be reaching peak charge), is it best to only charge to 80%? And if so, how would I do that with the current setting, would I have to charge to 13.6 or lower? Will that be good for the battery to be charged lower? Will it takes ages?

Sorry for the lengthy questions, I am just slightly concerned that charging to 100% each time I run the van will eventually damage the battery or lower its life? Considering it took me ages to get the cells from China, I want to make sure the yard ok.

If I am worrying over nothing, maybe the settings are just fine as they are!

Thanks for any advice!

 

[Rocketman]

1. you want the bms to be last resort. So if everything is working correctly it NEVER shuts off or down. So you want its settings to be a bit wider than your charger.

For example, bms my cut-off (if I remember correctly) is 3.65v /cell which is 14.6v. My chargers normally charge to 14.2v (occasionally I will move it to 14.4v - for a longer top- balance).

That way the charger works just like it should.

2. For best long life lithiums don’t want to be full all the time. With the sterling charger can you wire an on/off switch so at the drivers seat you can stop the charging? Hopefully so.

Also do you have a good shunt based battery monitor (like Victron Smartshunt or BMV712- there are others too)?

One thing you could do is after using the battery stop it’s charging at like 60-70%, let it sit until just before you are going for another weekend, then charge it the day or two before going.

Good Luck!

 

[mikefitz]

Suggest the following,
BMS, set cell volts limit higher, say 3.60 and pack limit to 14.4. Charger voltages should idealy be lower than BMS protection limits
Use a custom profile in the Sterling charger, 14.0 volts charge and 13.4 volts float, absorbtion period 30 minutes .
If you have the need to keep to less than 100% SOC reduce the charge voltage to 13.5.
If you continuously charge less than 100% it's possible the cells well exhibit a memory effect, thus reducing battery capacity. A regular full charge will correct this condition.

 

[Beanis]

Thank you both, that's great advise

Rocketman, I do have a kill switch for the Sterling charger, so I can easily turn it off and on, and keep the battery at a lower charge when not in use.

So from what you are both saying, I need to use the BMS as backup protection rather than the regulator of the charging current + amps.

I think the 14v pack charge and 13.4 float is sensible.

Last Q: Will this be ok for balancing, if I have balance set to start at 3.37 per cell?

Thanks again, great help!

 

[Rocketman]

I am not a balancing expert at all. But 3.37 = 13.48v which I think (but I don’t know) is too low to start the balancing. I think you need to start it at least at 3.5v -14.0v.

 

[Beanis]

I've done some reading and the general on the forum seems to be start balancing at 3.4 on the cells. That would be 13.6.

So i guess if I go for a 14v or 14.2v bulk, 13.4 float, and 3.4 balance, i should be ok.

Just not sure whether 14 or 14.2 is best, maybe i'll try both and see if I can perceive any difference

oh and of course set BMS to 3.60 and pack limit to 14.4

 

[Beanis]

And heres a final question : So In actually need to float the battery?
Considering that the only time I am charging the battery is when driving (there is no solar), so it is under no load at all when driving.
The only time it will be under load, it will not be charging.
So should I disable float?

 

[Pim57]

Float at 13.4 is not a problem. When the SOC is 100% there will be no charge current at 13.4 V.

Disabling float altogether is also good.

 

[RV10flyer]

My Victron 12-24/15A charger is set to charge to float only, or 27.0V. I let my SCC or Magnum 4024 do the Bulk/Absorb charging at 28.0V when V reaches my reboost setting of 26.4V. Divide by two for 12V systems. Victron is BT so I can change it in 1 minute if needed.

 

[Beanis]

Float at 13.4 is not a problem. When the SOC is 100% there will be no charge current at 13.4 V.

Disabling float altogether is also good.

Hmmm what is odd, is that the Sterling says it is in float mode now, but the BMS is telling me that around 3amps is coming into the battery. Maybe it's just topping it off.

I may well disable float, as I don't think it's entirely necessary for my usage

 

[mikefitz]

If you have Sterling default setting for float it's 13.8 volts. This voltage will fully charge the battery, thus for low stress, a lower voltage below 13.5 volts is needed for a constant float voltage.

 

[Beanis]

I've set at 13.4 - but am wondering if I should just turn float of altogether. I'll have a play around and see what works best.

 

[RV10flyer]

I've set at 13.4 - but am wondering if I should just turn float of altogether. I'll have a play around and see what works best.

Like the above poster said, 13.5V or below is fine for float on LFP.

 

[Beanis]

Great - all set. Thanks so much everyone, so helpful