Victron MPPT 75/10 never charges battery - Resolved, blown 20a fuse on bottom of MPPT

NMSunshine

Hi all, I know the performance of the Victron MPPT 75/10 in the TAB is hotly debated, but I cannot seem to get any charge into my battery from solar even after letting it sit for days at various states of charge / discharge, checking wires and fuses etc.

I have been trying various tests for the last 10 days or so to try and figure out why the solar doesn’t ever charge the battery. Detailed list of what I have checked so far below, I am trying to tell how I could determine if the Victron MPPT has gone bad, or any other tests I could run. I fully admit there could be something obvious I have missed but I'm scratching my head...

I added a Victron SmartShunt last week to actually see current in (none comes in) and out of the battery, current discharges but never comes in even when solar has good voltage/high generation, loads are disconnected etc.  Shore power charges battery fine and it will charge off an external NoCo charger. 

This is a new-to-us 2021 TAB 320ss Boondock, stock Victron 75/10 MPPT.

Interstate brand  SRV Group 24 flooded lead acid battery 81 AH that the previous owners got with the trailer. Low capacity I know but that's not the complaint. 

I know about the Victron 5v difference between battery and solar generation, and I am located in New Mexico where we regularly get solar voltage in the high 18v+ ranges according to the SmartSolar app on the Victron, so it has plenty of solar voltage to charge on those days in theory. 

Victron settings are defaults but match what I see in the Victron manual and  have seen from other Victron forum posts as supposedly working for Flooded Lead Acid. Minimum soc set to 50% etc. Charger is ON in settings etc.

I setup a ve.direct local network (Victron's local bluetooth device communication so devices can know about each other) and connected both MPPT and Smart Shunt to it.

Since the battery is a couple years old, fully charged the battery with a NoCo 10amp smart charger and confirmed it charges above 13v and holds a charge close around 12.8v when sitting disconnected for 24hrs. Based on charge behavior it seems healthy outside of the camper though I am sure its lifespan is getting short. My concern isn’t with the battery but I wanted to try to rule out any weird battery behavior contributing to the lack of solar charge output I am seeing. 

Steps I have tried so far after reading a LOT of forum posts here and elsewhere: 

First make sure everything seems connected right…

1) Checked all fuses, [Edit - I forgot the 20A fuse In the MPPT itself, see reply below] wires etc for continuity with a multimeter - not just visual inspection. 

2) Saw posts about PV being reversed so confirmed both by visual inspection and with multimeter that battery and solar connections are not wired in reverse. (Reversed polarity gives a negative voltage reading, these are all positive voltages)

3)  If I disconnect the battery wires at the MPPT and check voltage coming in from the battery thevoltage over the wires exactly matches voltage directly on the battery terminals so no noticeable voltage drop. Tells me the wires to the battery are good.

4) With battery connected to the Victron at night, with no solar generation, no loads, check the voltage at the Victron battery connector terminals - exactly matches the voltage measured directly on the battery terminals which tells me my connections at the Victron terminals are good.

5) Check solar voltage at the Victron PV terminals and confirm it matches what the SmartSolar app is reporting at the same time which tells me my pv wires and connections are good I think.

6) Nothing connected to Load terminals as I saw this is a frequent mistake as well. 

Now, run a load (12v fridge, fan etc) for a bit to run down the battery and monitor the Solar and Smart Shunt readings to see if it ever charges. 

Run the battery down to ~77% per the smartshunt which I assume should be fine to tell the solar charger to charge it, assuming sufficient solar voltage.

Turn off the load and wait a day or two to see if it ever charges. 

7) Regardless of battery state of charge or high solar generation (+5v greater than battery charge per Victron's charge algorithm) I never see current going into the battery.

Never sends charge. I have seen solar voltages at 19v occasionally and still no charge into the battery. 

Smart shunt state of charge just sits at 77% and zero current all day in spite of a full sunny day with all loads disconnected and solar connected. I know the soc isn't totally accurate but it should allow the battery to charge?


8) History in the Smartsolar shows the same - zero yield over several days. Same for the entire time I have had the van. Not sure why SmartSolar is showing 14+v to battery, the battery never sees that so I assume it's what it THINKS it is sending. 

I have heard people say it won't charge if the battery is "Too full" but I can run the battery down to various %s according to the smart shunt and still never get charge going into the battery. Occasionally it will flip to 0.1A on the LOAD output for a while (there is really NOTHING on the Load) but never long enough to actually charge.

Appreciate any thoughts on what to try next?

NMSunshine

Forgot to note I also checked the battery cells and they are all full/not dry, assuming someone topped them off at some point as I wouldn't expect them to stay full for 3+ years (?)

rfuss928

Did you check this fuse?  It is kind of hidden by the wiring and hard to see from above.  A small mirror may help...

NMSunshine

@rfuss928 I did NOT check that one! And what do you know, it's blown!! Will have to wait for the sun to come up again to see if replacing it took care of things. I will post back, thanks!

NMSunshine

Looks like that fuse was it, it's charging now, woohoo! Thanks again @rfuss928

I happened to be out there right when the sun got high enough to cross the 5v threshold and could see it kick into charging mode in real time. Couple of screenshots just to illustrate, pretty cool. 

Right before it cut over (battery voltage +5v is the cutover threshold)
 


Charging starts once it hit +5v over battery voltage , solar voltage is drawn down immediately by the charger load and current starts flowing. 


Device list quick view in the Victron app:
 


Later in the day with the sun more overhead:




Not sure what's "normal" for a sunny day in September at 5,300 feet in Albuquerque but at least we're getting charge now