MT50 Remote MPPT Controller - Bulk time set-up

[sirweste]

Afternoon all,

I fairly sure I know the answer to the following; it's not possible.

Can the MT50 be set-up to make the bulk charge time significantly longer. I have 6 off T-105 batteries wired in 12 V with a paltry 200 W of panels fixed flat. The time at bulk charge voltage (I have set-up all my charge voltages) is limited to only 2 hours (or was it 3) and I find that it would be better if it was not limited to such a short time. Can it be adjusted?

I know one way would be to change the float voltage to the same as the bulk, but this is risky if I'm away from the boat for a sunny weekend I think

 

Cheers

[WotEver]

I think if it were mine I'd set float at 14.6V. A day or two at that isn't going to hurt T105s although they might need a little drink a bit more often. 

[Dr Bob]

On our sailing yacht we had 440Ahr domestic bank and a single solar panel giving 6Amps max. We too set the voltage at 14.6V and had no problems in the Sun in Spain, Italy, Greece etc. The one panel was certainly not too much to cause problems - the batteries lasted 5 years+. In your case you will have more amps going in but likely less sun. You will only get that power going in for 30% of the 24hr day, ie 8 hours. Maybe if you are worried just connect up one panel when you leave the boat if there is no load on the bank.

[sirweste]

I hadn't really considered the measly current they would be supplied with, I was just concerned with them being boiled for a weekend while I wasn't there. But you guys are right, I shall adjust the float p.d. to effectively make it bullk only charge.

 

cheers for the advice

Edited April 27, 2017 by sirweste

[WotEver]

41 minutes ago, sirweste said:

I shall adjust the equalise p.d. to effectively make it bullk only charge.

Presumably you meant 'float' voltage?

[sirweste]

I did, corrected, ta

[sirweste]

Right, changed float to 14.8 V and this morning it was at 13.3 V at 5.7 A with the PV at 18.7V and 4.0 A. Still not the bulk figure I've told it to charge at. 

So I changed the Bulk Reconnection Voltage to 14.8 V too. Made no difference. 

Anyone any ideas how to make the wee bugger charge at what I tell it to!?

[Boredrider]

If your MPPT behaves like mine, it will not reach the max voltage setting until it has to.  What was the SOC when you took the readings?

[Detling]

How bright was the sun, was there any shade the PV seems low but I don't know what panels you have.  Today at 10am in full sun my charge was 17.5 amps at 14.2 volts but then I have 600 watts of panels (6 x 100 watt) connected as two parallel sets of 3. The bank was over 90% doc.

The voltage will go up when the bank gets fuller.

 

[sirweste]

14 hours ago, Boredrider said:

If your MPPT behaves like mine, it will not reach the max voltage setting until it has to.  What was the SOC when you took the readings?

This. 

It's very bloody frustrating, I want it to do as it's told! So if the panels are at more than the bulk setting it would expect it to charge the batteries at bulk!

I guess there are some losses, so if the panels are outputting 14.8 V then you can't expect the batteries to also get 14.8 V. The SOC was around 70% so it should have been in bulk. 

 

[Iain_S]

Comparing your figures with Detling's, they are in the right ball park, although there must be some inaccuracy in measurement, as you appear to be getting more out of the controller than is going in!

As others have said, the voltage should rise as the batteries S.C increases. At the time the readings were taken, they were in bulk charge, where the limiting factor is the charging system, which is unable to provide as much current as the batteries can take, so it's voltage falls.

[Richard10002]

Presumably an MPPT controller behaves a bit like a normal smart battery charger i.e. :

If my batteries are depleted, the voltage can start at say, 13.2V, with the Amps at the max the charger can produce, (80A in my case). This is the Bulk charging period, and the volts increase towards the user setting, (15V in my case), with the Amps remaining constant. Once the voltage has reached the user setting, the Amps start to fall and the volts remain constant, and this is the Absorbtion period.

it would not surprise me to see a voltage lower than my setting on an MPPT controller. I would expect it to be feeding its "max Amps", which I would guess could vary based on the sunlight and the panels.

 

I may, of course, not be understanding MPPT properly, merely a lower voltage during charging wouldnt surprise me, (even if it should  )

[WotEver]

1 hour ago, Iain_S said:

At the time the readings were taken, they were in bulk charge, where the limiting factor is the charging system, which is unable to provide as much current as the batteries can take, so it's voltage falls.

Yes, this.

It was supplying the maximum current that it could (5.7A) at the minimum useful charging voltage (13.3V). It wouldn't have wanted to drop the charging voltage below 13.3V to increase the current and there would be no point in increasing the voltage with a corresponding decrease in current. So it was outputting the maximum power available from the panels at that time. 

[sirweste]

understood. M<y understanding of charging was lacking. Cheers