No B2B strange charging observations (1 Viewer)

[Jeffr3y]

I did a one night wild camp which resulted in my Victron shunt app reporting my my leisure batteries level at 66% the next day.
Just as an experiment I wondered how long it would take for the engine on tick-over to bring the batteries up 1% at a time (I have no B2B)
Started at 66% after 8 minutes it went to 67% (it was showing just over 5 amps going in then that dropped to around 4.7-4.8 amps)
After 15 minutes I couldn't believe it, it had suddenly jumped to 100%!

I thought this is great if it wasn't a fluke, I don't need the B2B I had planned on getting and with just a 15 minute tick-over during the day I could wild camp indefinitely.

So with my 100% batteries I spent another night wild camping and the next day it was down to 66% again.

Tried a repeat of the experiment the day before but this time it never went higher than from 66 to 68% and I left it for over 30 minutes.
Does anyone know what could be going on here?

I also have a meagre 100w solar panel but don't remember if it was sunny on the first day and not on the second.
Is it possible for the alternator to recharge 2 110 a lithium's from 66 to 100% in 15 minutes or is the victron app lying to me? (although if it was it seems strange I had 66% left after the 2nd night I should have only had 33%.
Any ideas?

 

[Guigsy]

I suspect your shunt is thinking the charge from the alternator is the resting voltage of the battery, so it thinks it's full and resets it's counter back to 100%. I think it can be fixed in config?

 

[oldiesontour]

Alternator production of circa 160ah on tick over aven with the best solar possible no

 

[Just smiffy]

Your not doing your van any favours idling for 30mins at a time either, eventually clog up the EGR and causing other problems…

 

[ChrisL]

The shunt will tell you how many amps are flowing into the batteries and if you go into history and look at last discharge it will tell you how many amp hours were extracted from the battery, so if your last discharge was 20 Ahs and you are currently charging at 10 amps it will take two hours to recharge the batteries not allowing for inefficiencies.

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[DBK]

As Guigsy said, it's probably an anomalous reading from the battery monitor. These things count the amps in and out and can work out the state of charge from that but they also monitor the battery voltage and will use this to refine it's estimate of the state of charge.

For example, because I connected my B2B directly to the batteries it bypasses the shunt so the monitor doesn't know about the charging current from the B2B. The result is after say driving for an hour the monitor might think the batteries are at say 70% because that was what it was at the start of the journey. However, after a short period it will be showing 100% because it's worked out from the voltage the batteries were fully charged.

In your case I suspect the idling engine raised the voltage a bit on the batteries but did very little charging. The monitor saw a ready 12.5 volts, the resting voltage of a fully charged lead acid battery, and determined it was fully charged.

 

[ChrisL]

I think the shunt is probably not set up correctly for lithium or the default lithium settings are not quite right for his lithium batteries, I have found mine needed a bit of tweaking to get the SOC reporting correctly. I can post my settings if anyone is interested.

 

[Jeffr3y]

I suspect your shunt is thinking the charge from the alternator is the resting voltage of the battery, so it thinks it's full and resets it's counter back to 100%. I think it can be fixed in config?

So okay it thought it was full but it wasn't, should it not mean that the second day there should have only been 33% left in the batteries?

 

[Guigsy]

So okay it thought it was full but it wasn't, should it not mean that the second day there should have only been 33% left in the batteries?

Possibly. But as DBK said, where is you alternator wired in, with regards to the shunt?

The shunt should be the only thing connected to the battery terminal (negative side I think?) with everything connected to the other side of the shunt (it now becomes the battery terminal). That way the shunt should be able to see you're still pouring power in, so it's not full.

 

[AdrianChen]

I guess that on night one the Shunt must have seen the voltage from the alternator hit whatever the shunts "Charged Voltage" setting has been set to - (Typically set to 0.2v under "Absorbtion" setting so between 14.2v and 14.4v), it will then look to the "Tail Current" setting, which is typically 2-4% so with 220AH set as the battery capacity it would equate to 8.8amps or less and if the current going into the battery is less than the tail current (8.8amp) and the voltage is above the charged voltage for more than 3 mins ("Charged detection time" setting), it will assume the battery is full and set the SOC to 100%. It is quite possible for the alternator to get hot and limit it's output if running on tickover, since there will be little airflow from the internal fans.

The following day the shunt will be counting the amps used and subtracting them from what it started at - 100%, so reduces to 66% (even though the battery is at 33%)

Not sure why that all didn't happen again on the second day, but as you say, a difference in solar possibly.

I would have a look at the shunt settings (I know some folk set the charged voltage to 13.4 since that is a good resting voltage for lithium, but it's wrong), also in case there was some sort of reset, check the "Battery SOC on reset" setting - mine is on Keep SOC.

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[Jeffr3y]

Thanks for everyone's input, so basically a scenario where a normal van alternator (2015 Ducato 3.0 litre power model) can recharge 2 110 lithiums from 66% to 100% in 15 minutes is a pipe dream really, pity about that I'll have to still go with my B2B upgrade idea, I'd like to be able to stay off grid for longer but I do have a weakness for all my gadgets lol.

 

[Guigsy]

Thanks for everyone's input, so basically a scenario where a normal van alternator (2015 Ducato 3.0 litre power model) can recharge 2 110 lithiums from 66% to 100% in 15 minutes is a pipe dream really, pity about that I'll have to still go with my B2B upgrade idea, I'd like to be able to stay off grid for longer but I do have a weakness for all my gadgets lol.

That would need about 300amps. Well beyond what the alternator can provide. And the batteries would be toasted too.

But how long do you stay still for? Running down the batteries over a few days is fine if you drive for a couple of hours.

If I were you, I'd sort out my shunt to figure out what my daily average is first. Then think about b2b and solar. I'm actually finding 175w solar and a 30A B2B has been fine. But I'm not using anything that needs an inverter and my fridge is on gas when off grid.

 

[Lenny HB]

Your not doing your van any favours idling for 30mins at a time either, eventually clog up the EGR and causing other problems…

Yep one of the best ways of wrecking an engine, modern diesels should be driven straight off after starting.
On tickover from cold they never get up to operating temperature resulting in wrecking the CAT & DPF, glazing the bores etc.

 

[ChrisL]

If I were you, I'd sort out my shunt to figure out what my daily average is first. Then think about b2b and solar.

As Guigsy has said sort out your shunt first so you know what your using and what you're putting back in.

The following video by fellow member RogerIvy of Offgrid Power Solutions should give you a good starting point and may well be close enough to not need further tweaking.

 

[Tombola]

Don the lithiums have a BMS you can refer too

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