I have two charge sources for my NMC Lion house battery. 1st is a 100/20 MPPT Smart Solar and the 2nd is an Orion XS which charges the NMC from the starter battery which is fed by the alternator and a second solar array (with it’s own PMW charge controller).
Both are connected to my Cerbo GX with DVCC enabled but only for V, I & T sense, not charge control.
The MPPT and Orion use exactly the same charge profile. The charge profile I have at present has an Absorbsion V of 11.6v and a Float of 11.0v. I have set the Re-bulk offset value to 0.01v. I use this profile when the RV is parked up for extended periods so as to keep the NMC battery near its nominal V with a gentle 20% DoD cycle.
The Orion XS has a settable Re-Absorbsion time, which I have set to 7 days.
The MPPT, despite sharing the same saved “preset” charge profile does not have this setting.
The Orion XS behaves exactly as I would expect. It gets its V and I from the Smart Shunt via the DVCC of the Cerbo. It bulk charges to 11.6v, it then goes into Absorbsion for a couple of hours and then into float and storage. It stays in storage until V Batt 10.99 or 7 days pass. Perfect.
The MPPT with identical settings (minus the 7 day Re-Absorbsion, which the MPPT doesn’t have) goes into Bulk each and every morning meaning that rather than a gentle 75% to 55% SOC that I desire.
It’s not the end of the world but just annoying that I can’t fathom why the MPPT behaves in this way.
Is it simply that an MPPT starts a new charge cycle every day?
Yes, the MPPT starts a new charge cycle every day, they are not great for holding batteries in storage. there are potentially 2 options, one I used to do on my boat when not in use was to reduce the absorption voltage. The other option could be to use the limit battery voltage in DVCC, but I am not sure if this works for uncontrolled aka dumb batteries.
Thanks for the confirmation that I’m not going nuts, although it’s been driving me nuts. I can create a workaround, but I just couldn’t workout what I was doing wrong. If the MPPT restarts every day, there’s little I can do about it other than patiently wait for a firmware update, which might be a long time coming
This is unlikely to be changed in any firmware update.
It is needed for most pv systems in regular use, rather than for those in park mode. As you are using DVCC, I would use that to limit the Abs charge voltage, rather than frequently changing the value programmed into the MPPT, as that will eventually damage the EEProm memory.
It’s going into Bulk each and every morning even though the parasitic draw on the system (when it’s parked up) only drops V Batt by approx 0.08V per day but it’s going into Bulk when V Batt is 11.52v for example.
If you re-read my initial post, what I was expecting to happen was a slow drop over the course of a week or so at 0.08v per day then V Batt drops to 10.99 and Re-bulk is triggered. But this doesn’t happen, or rather it happens exactly like this on the Orion XS if I take the MPPT out of the equation but the MPPT behaves differently.
pwfarnell seems to have hit the nail on the head I think when he said that the MPPT chargers start a new cycle every day. Annoying but seemingly true.
The charge controller will start a new charge cycle every morning, when the sun starts shining and when the PV voltage is 5V higher than the battery voltage.
Well now I feel stupid, but at least it’s not driving me nuts that I can’t figure out why it won’t behave as I want.
As a fix I’ve simple set a 11.0v Absorbsion voltage for the MPPT thus essentially disabling it, leaving the Orion XS and it’s independent solar array to do all the work once the battery gets down to 10.99.
Not my preferred solution but I’d rather the NMC have a shallow 20% DoD cycle rather than sit between 11.55 and 11.60 for months on end.
Apologies for wasting your time, but I for one learned something. Read the manual. Dooh
