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eyacht avatar image
eyacht asked

MPPT not charging but Victron Connect says it is

Hi everyone - I have an odd situation that I hope someone can shed some light on. I have an MPPT 75/10 that has my 48V propulsion bank connected as PV in and the battery out goes to my starter battery. There is no load connected. In the Victron Connect app, everything looks great - battery voltage is 13.4V and it's in float. I just went to turn on the generator and got no power at the panel. Having checked the breakers I took a voltmeter to the starter battery and it's completely dead - 3.5V. I have no idea how the app can read healthy voltage and the battery is pretty much dead. Any thoughts? Thank you in advance.

EDIT 10 Aug 23 - I followed advice and measured voltage from MPPT + to battery - and from MPPT - to battery +. The first was 2.4V and the other 10.3V so there is an issue somewhere with the positive wire from the MPPT. I suspect a dodgy fuse holder. Thanks everyone for your input and advice.

battery chargingMPPT SmartSolarAGM Battery
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2 Answers
wkirby avatar image
wkirby answered ·

If the MPPT reads 13.4V and the battery its self reads a different Voltage then that means that the battery is not connected to the MPPT for some reason, perhaps a wiring fault or a blown fuse or open circuit breaker.

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eyacht avatar image eyacht commented ·
The wiring is pretty straight-forward as described above .. but why would a blown fuse or open circuit breaker cause the MPPT to read 13.4V? If the breaker or fuse to the battery has gone, wouldn't it read zero?
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seb71 avatar image seb71 eyacht commented ·
The MPPT would output voltage at its battery terminal if it has voltage at PV terminals from a PV array, even if not connected to a battery at battery terminals.


But you should not connect PV without a battery on battery terminals.
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eyacht avatar image eyacht seb71 commented ·
Really? I thought it would read the battery voltage. So you're saying the reading in the app (and at the MPPT battery output terminals) is the "produced" voltage and not the actual voltage at the battery?
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seb71 avatar image
seb71 answered ·

I have an MPPT 75/10 that has my 48V propulsion bank connected as PV in and the battery out goes to my starter battery.

Do not use a battery as PV input for any MPPT.

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eyacht avatar image eyacht commented ·
Why not? Input voltage is input voltage; panel or battery doesn't matter.
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Alexandra avatar image Alexandra ♦ eyacht commented ·

@eYacht

It is outside of intended product design and use. There is a product whose intended use use is DC to DC charging - ...orion....

Mainly because the short circuit current for a battery is higher than the PV input is designed for.

The second is it is an mppt so meant to track its input.... A battery cannot be 'tracked'.

Basically it can't protect anything if it needs to without self destruction.

Likely in your setup right now the fuse has blown on the unit. Hopefully that is all that is wrong right now. Since you have no errors that is likely it.

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eyacht avatar image eyacht Alexandra ♦ commented ·

Thanks for the added detail @Alexandra. I looked at the Orion TRs for this but they only have a 48/12V in the TR series and not the TR Smart series. The fine print in the TR series says not to use it for battery charging and to use a TR Smart instead. Since they don't make a 48/12 TR Smart, that wasn't an option.

I just went to check the internal 20A fuse and it's fine with good continuity across it. I also installed an inline 15A fuse and it too is fine. If it wasn't for the dead battery everything looks fantastic! I checked the voltage across the battery terminals on the MPPT and got 13.4V; the PV input reads 53.2V, which is well within tolerance.

This is supposed to be a trickle charger to keep the start battery at float so there shouldn't be a big pull on the PV input. When I installed it, it went through the bulk, absorption, float cycle perfectly and it then sat there at 13.4V like it's supposed to. No fuses are blown and there are no breakers in the circuit, so I just cannot work out why the unit thinks the battery is reading 13.4V when it's not.

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Alexandra avatar image Alexandra ♦ eyacht commented ·
@eYacht

Something has died internally in the mppt.

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wkirby avatar image wkirby ♦♦ eyacht commented ·
If you can read 13.4V on the MPPT battery terminals then disconnect the battery cables from the MPPT and measure the Voltage on those. It should read 3.5V (or whatever the battery Voltage currently is). I suspect you'll read 0V on those cables pointing towards a disconnection between there and the battery. You'll have to trace backwards from there to find the fault.
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eyacht avatar image eyacht wkirby ♦♦ commented ·
I have continuity from the battery + to the MPPT battery + and the same with the ground wire, so that rules out a disconnect from the MPPT to the battery.

I just cannot understand how there is 13.4V at the MPPT battery terminals and nothing at the battery.

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wkirby avatar image wkirby ♦♦ eyacht commented ·

That's because the MPPT is in float mode and the target Voltage setting for that is 13.4V, so the MPPT is doing what you have set it to do. The MPPT measures battery Voltage at its terminals. It cannot measure the Voltage of the actual battery terminals if it is not connected to them for whatever reason.
It is physically impossible for the battery terminals to measure 3.5V and the MPPT terminals to measure 13.4V if they were connected together. A small Voltage drop would be acceptable in proportion to the current flow.
This is why I keep going on about your battery not being connected somehow.

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eyacht avatar image eyacht wkirby ♦♦ commented ·
Thanks @WKirby ... I'm 100% sure the wires from the MPPT are connected to the battery - continuity in both fuses and continuity from MPPT to the battery through both the + and - wires. It's not a complicated installation and it's less than 3m of wire from one to the other. I wonder if the MPPT is not reading the battery voltage but simply the conversion voltage set (13.4V in this case) because the battery is totally shot beyond recovery.
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nesswill avatar image nesswill eyacht commented ·
Hi

You say ground wire do you mean negative wire?

If you turn the MPPT off do you still have 13.4v at the MPPT positive and negative terminals?

What happens to the 13.4v if you put a reasonable load on the system?

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eyacht avatar image eyacht nesswill commented ·
Yes - sorry - I mean negative wire. You can't really turn it off, you can only disconnect the source & output. Voltage doesn't move much with a 1800W draw.
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nesswill avatar image nesswill eyacht commented ·

Ok so have you disconnected/isolated one of the PV cables, say the negative and check the volts across the battery terminals on the MPPT positive & negative. And please post the voltage reading here.

Then check the volts across the terminals of the first battery/bank (still with the negative disconnected). And please post the voltage reading here.

Then check the volts across solar terminals on the MPPT (still with the negative disconnected). And please post the voltage reading here.

FYI - continuity can be misleading and should not be checked on a "live" circuit. An Ohms reading will tell you the resistance and this can be done between each connection in a circuit (finds high resistance i.e., a bad or loose connection), but this ideally should only be done unpowered, but this is not always possible or practical.

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seb71 avatar image seb71 eyacht commented ·
Funny that you got all those precautions for a DC-DC charger, but then you connected a battery to the PV terminals of an MPPT.
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eyacht avatar image eyacht seb71 commented ·

By "all those precautions" you mean an inline fuse? That's normal and the installation instructions say to put one in even if / though the unit has an internal fuse.

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