L/Battery - go large or go lithium?
- Thread starter Chris1983
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- dc - dc charger victron vsr
It will depend on the health of your starter battery. I see it’s at 12.2v so the Ablemail will be giving it a top up every 15secs or so. You will see this as an increase in the current on the shunt - ramp up to 2-3A for a couple of seconds and then back to zero - and repeat. My SB is on its last legs so the Ablemail is keeping it going, plus I leave a USB plug in and my dashcam is on parking mode and has a small draw. With no charge to the LB and the van stationary for about 10 days my LB is down to 87% - all to the Ablemail. The SB has been kept at a constant 12.2(and a bit) volts. It’s doing its job and has meant I’ve not had to replace the SB which I would have done without it!
It doesn’t need any charge or input to the LB, it simply works of voltage differential.
It doesn’t need any charge or input to the LB, it simply works of voltage differential.
I’m hoping to get some feedback on screen grabs.
Solar currently off van as getting wrapped pop top tomoz.
Left work tonight, LB at 92, quickly jumped up to 94 via bulk charging DC to DC.
That is when the DC to DC dropped into absorption state, and the current dropped right down. SOC never moved past 94 on hour commute from shift.
Is this normal? Do I assume the SOC is more likely 100% as current dropping so low? Should the state of DC to DC then not read ‘float’ if this is correct?
Should I stop concerning self?
Screen grabs if helpful to this query.
Thanks all.
Solar currently off van as getting wrapped pop top tomoz.
Left work tonight, LB at 92, quickly jumped up to 94 via bulk charging DC to DC.
That is when the DC to DC dropped into absorption state, and the current dropped right down. SOC never moved past 94 on hour commute from shift.
Is this normal? Do I assume the SOC is more likely 100% as current dropping so low? Should the state of DC to DC then not read ‘float’ if this is correct?
Should I stop concerning self?
Screen grabs if helpful to this query.
Thanks all.
Just some more info. Checked fogstar BT and had battery 100% soc. so changed that in settings of shunt. Thinking that would calibrate all things.
Another hour of driving and DC to DC still not moving into float mode despite current dropping to nothing.
Another hour of driving and DC to DC still not moving into float mode despite current dropping to nothing.
I believe it can sit in absorption for quite a long time trickling current in (that 0.3A should gradually decrease over time) but it should end up in float eventually. I wouldn't worry about it, maybe just check again at some point in the future when it's had a long time sitting there on charge and without load. All these measurement gizmos can be useful, but they're not worth obsessing over - there's no indication to me that there's anything wrong with your system.
Thank you!
I appreciate the time taken to reply. Still trying to upskill/ up knowledge!
Bw
Chris
Second @t0mb0 and @TallPaul_S general advice here. Getting used to what's "normal" for your install is a good idea so you notice if something changes, but focusing too hard just causes worry. The important thing is the outcome, so long as you have reliable leisure power you're good 
Sorry to bore.
Reattached roof solar panels post wrap.
Numbers just aren’t making sense, to the point where I am not sure what use shunt is in my system.
Not obsessing, just trying to understand.
Bleak overcast weather (wet and windy).
Panels working but saying ‘absorption’, shouldn’t then be in bulk as shunt reads battery at 74 %.
I have then checked BT of battery which has battery as 80+%?
Thoughts?
Reattached roof solar panels post wrap.
Numbers just aren’t making sense, to the point where I am not sure what use shunt is in my system.
Not obsessing, just trying to understand.
Bleak overcast weather (wet and windy).
Panels working but saying ‘absorption’, shouldn’t then be in bulk as shunt reads battery at 74 %.
I have then checked BT of battery which has battery as 80+%?
Thoughts?
You're right that you'd expect to be in bulk charge at that state of charge of the battery. However, given it's only running on solar, and the solar can currently only supply a tiny fraction of the rated bulk charge current then the distinction between the two is academic. The thing is, an MPPT in general doesn't actually 'know' what the current state of charge is, it can only infer it from the amount of current flowing at the set voltage. The current in this case is limited, not by the battery itself but by the ability of the panel to supply it, however my guess is that the MPPT itself has no way of distinguishing between these two situations and so it's assumed an absorption state. I don't think this is a problem as the battery is getting charged with what little power there is in any case.
You can verify this by firing up the engine, in this case I would expect the DC-DC to start dumping in whatever the full bulk charge current is and correctly identify a bulk charging state from this.
A lot to learn still!
Shunts are not perfect devices, they work by integrating current flow over time and, especially if it's been a while since they last 'synced' at 100%, the error does accumulate over time. It's not possible to know which one is more correct with complete certainty but in this case I'd be tempted to believe the victron shunt more because in-built battery shunts can often be poor at measuring small current flows and so will often overestimate charge when they've been sitting there with low outgoing current for a while.
Although all 3 Victron devices show in the app they are not talking to each other (unless you set that up - I think they all have VE bus) so the MPPT doesn't know that the Shunt thinks the battery is 74%
As @t0mb0 says it can only use the information it can measure, and with a voltage as seen by the MPPT of 13.43v which is pretty much 100% for a lithium based cell.
I remain puzzled by the difference in voltages in your system, some variance is to be expected but Victron is good kit so a difference of 13.43 Vs 13.34 when both devices should be pretty directly and cleanly connected to the same battery is odd.
As @t0mb0 says it can only use the information it can measure, and with a voltage as seen by the MPPT of 13.43v which is pretty much 100% for a lithium based cell.
I remain puzzled by the difference in voltages in your system, some variance is to be expected but Victron is good kit so a difference of 13.43 Vs 13.34 when both devices should be pretty directly and cleanly connected to the same battery is odd.
Thank you sir,
In relation to the differences. Is there any troubleshooting I should be aiming to do?
I have a few days off coming, I could investigate further if provided with some direction?!
Normally the risk with a long cable is voltage drop so you'd expect the voltage to be lower if you just measured it with a meter at rest.
However in this case the MPPT is a source of voltage so the drop to be concerned about is the other way around, if the voltage is rising the MPPT will assume it's the battery starting to resist charging as it nears capacity but it could also be due to loses in the cable. Lithium voltage ranges under charge are a much lower range than lead acid so voltage drop can have more of an impact, it's why some chargers have a very low current (so low voltage drop) sense wire to get a more accurate reading.
What size is the wire, then we can work out the expected drop and see if the numbers seem plausible.
However in this case the MPPT is a source of voltage so the drop to be concerned about is the other way around, if the voltage is rising the MPPT will assume it's the battery starting to resist charging as it nears capacity but it could also be due to loses in the cable. Lithium voltage ranges under charge are a much lower range than lead acid so voltage drop can have more of an impact, it's why some chargers have a very low current (so low voltage drop) sense wire to get a more accurate reading.
What size is the wire, then we can work out the expected drop and see if the numbers seem plausible.
What size is that cable between the MPPT and the battery?
There will be some voltage drop over the cable, but that is a function of current flow (and cable resistance given V=IR) so given only 0.9A was flowing you wouldn't expect that to be very big. Next time it's dumping a decent amount of current in, you can check the relative voltages then to check nothing is amiss there.
As it is, slight variation in measurement, possible slight differences in exact sample reading time will mean some natural variation in the reported value.
Battery ‘size’ is whatever I was told to use in this thread (I really have been hand held the whole way). Does 6mm sound right?
It’s only the red that is long (wardrobe behind cupboards down side of sink unit and under driver seat) the negative is not long.
Not sure if that helps?
Am I risking ka-boom?
It’s only the red that is long (wardrobe behind cupboards down side of sink unit and under driver seat) the negative is not long.
Not sure if that helps?
Am I risking ka-boom?
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