Dual MPPT charges, one battery bank (1 Viewer)

[Nigel Crompton]

How does this work?

AFAIC a battery charger senses the the voltage of the battery and supplies an appropriate charging current.

If that's correct how does the second charger know what current to supply, if it's being 'fooled' by the voltage across the battery caused by the first charger ?

 

[Tombola]

if the parameters are set the same, and the solar panels etc on each MPPT all match up its possible

Some , like the victron VE can talk to each other I believe.

 

[tonyidle]

The charger outputting the higher voltage wins.

 

[Guigsy]

If they've got the same charge profiles (probably best to stick to the same brand) AND similar cable runs (so there's no significant voltage difference), then they should work together. The reality is that it probably doesn't make much difference through most of the charge range, but at the top end, they might confuse one another... unless they are actually communicating like the Victron bluetooth connect that can send the actual battery voltage measured at the shunt to all the devices.

 

[nabsim]

I have had two ppt controllers for years, each has a 150W panel connected, one is a Votronic and the other is a Victron. I have the app for one and a display for the other and they are always within 0.1A of each other.

This is not the same when I run my 2 x 30A mains chargers however, one will drop back a bit doing less work.

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[Nigel Crompton]

I have had two ppt controllers for years, each has a 150W panel connected, one is a Votronic and the other is a Victron. I have the app for one and a display for the other and they are always within 0.1A of each other.

This is not the same when I run my 2 x 30A mains chargers however, one will drop back a bit doing less work.

Thanks for this ... I guess I knew that it 'worked' somehow, and I can see that Victron et al have devices that communicate, but with two different chargers HOW does it work ?

If the charger with the highest voltage wins, what's the other one doing - sensing that the battery is already charged and shutting down ?

 

[Carpmart]

Neither MPPT needs to know what the other is doing.. further, the battery BMS doesn’t care where it’s getting charge from, multiple MPPT’s, B2B, mains it doesn’t care. When it’s full, all charging devices will understand that based on their working parameters, so they slow down or stop. If they don’t, then the BMS has the ultimate say and doesn’t allow any more in.

 

[LithiumConvert]

The charger outputting the higher voltage wins.

Exactly.

And this means that a charger with a potentially higher charging current can effectively be turned off because of its lower output voltage.

 

[Guigsy]

I used to assume that when a charger was set to 14.2v, then that's what it'd throw out when charging. In reality, that's the voltage it's aiming for. But unless it can overwhelm (and cook) the battery, it'll be pumping in as much current as it can at a voltage a bit below 14.2v. It'll be dragged down by the battery. Hence another charger running in parallel with a 14.2v target will also pump in what it can, but it'll be dragged down to the same level. So they'll both stay active. It's only when the battery gets close to it's target voltage (absorption mode?) that the chargers might fight.

 

[funflair]

I used to assume that when a charger was set to 14.2v, then that's what it'd throw out when charging. In reality, that's the voltage it's aiming for. But unless it can overwhelm (and cook) the battery, it'll be pumping in as much current as it can at a voltage a bit below 14.2v. It'll be dragged down by the battery. Hence another charger running in parallel with a 14.2v target will also pump in what it can, but it'll be dragged down to the same level. So they'll both stay active. It's only when the battery gets close to it's target voltage (absorption mode?) that the chargers might fight.

We had two Votronic MPPT regulators on the last van and they worked perfectly well as you describe, yes one would switch off when the charge got close to 100% but that's no different to one big regulator cutting back it's amps, I wouldn't say that they particularly faught.

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[autorouter]

How does this work?

AFAIC a battery charger senses the the voltage of the battery and supplies an appropriate charging current.

If that's correct how does the second charger know what current to supply, if it's being 'fooled' by the voltage across the battery caused by the first charger ?

The first stage (bulk charging) is very simple. If the battery voltage is below the absorption voltage setting (about 14.5V), the two chargers will both push out their full amps rating. When the voltage reaches one of the absorption voltages, that charger switches to the absorption stage. The other one might switch a few minutes later, if its absorption voltage is set a bit higher. But at that point it's about 80% charged anyway.

In the absorption stage, the chargers give out a fixed voltage and monitor the current each is pushing out. If one is trying to assert a slightly lower voltage than the other, it will ignore the slightly higher voltage because now it is only monitoring the amps. As the battery emf (what would be its rest voltage) rises, the amps from each charger will fall. When each gets to the predefined 'tail current' (usually about 1/10 of the maximum amps) it will switch to the float stage.

 

[peterc10]

I have 4 solar panels. I use 2 MPPT regulators with 2 solars on each, one is a Votronic (with 250W) and the other is a Victron (with 200W). All of this is monitored by a Victron BMV. The Victron stuff is on bluetooth . With solar charging only on the BMV tells me how much the total net charge i.e. charge minus discharge. The Victron MPPT regulator tells me how much charge it is putting in. The difference is what the Votronic is putting in less he discharge.

This morning in the sun I was in the motorhome doing a bit of work, and so not much discharge. The mains charger was turned off, as it has been for most of the winter. The BMV showed the net charge hovering around 6A and the Victron regulator showed that its output hovered around 3A. Therefore the other 3A must be made of what was coming in via the Votronic regulator less some small discharges. So it can't be a case of one wins and the other cuts out.

 

[AdrianChen]

We have Victron MPPT's a 100/20 with 200w and 100/50 with 350w, if they were identical spec and settings, with identical wiring they would just operate much as autorouter describes, however in practice the panels dont get exactly the same amount of sun because they're dirty, and because when the sun is low they get different shadows cast by the aircon, fridge outlet etc. Added to that our wiring between the MPPT's and batteries is not identical, so we end up with similar outputs but not identical.

Because we use Victrons facilities the chargers synchronise their state/charge profile, so when one hits Absorption, the other is set to absorption. They also share the battery voltage taken from the shunt so are working on the correct battery voltage not one measured/reported at the MPPT output terminal, it's the same with the battery temperature which is shared so that if under 5°c neither will charge. For the last two days the output looked like this.....

 

[nabsim]

Thanks for this ... I guess I knew that it 'worked' somehow, and I can see that Victron et al have devices that communicate, but with two different chargers HOW does it work ?

If the charger with the highest voltage wins, what's the other one doing - sensing that the battery is already charged and shutting down ?

I don't know how or why it works, I just now that it does with both my mppt controllers. I know it does as I have the app on the Victron and the LCD display add on for the Votronic DUO, (before they did bluetooth options).

As I said this is not the case with my 2 x Victron 30A mains chargers, one of them will drop back to a lower current BUT they do still put charge into the battery's. Instead of getting the full 60A until battery are charged it will drop to around 45A, still worth me running both but not what I expected.

 

[Richard n Ann]

I've got 2 votronic controllers. One is on a 100w portable folding panel and is only used when cloudy.
When both on, the charging current is all from the main 150w roof panel (typically 2 amps when cloudy) and the portable panel doesn't add any charging current. but when the compressor fridge starts the second panel must contribute because the battery doesn't discharge.

So with my set up the battery won't charge faster but it does what I need it to.

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[oldiesontour]

Got a nice sunny day here in Lincolnshire so first test of new foldable (rigid) panels and roof mounted through 2 completely different controllers.
First put 3 way on 12v then compressor freezer then diesel heater left for a couple of hours.
Switched all off left and hour,plugged in foldable app says charging 8 amp (240w panel not in best spot but decent light)
Then switch on roof panels(400w)
App says 11/12 amp charge
These are Roof via Renogy b2b mppt
Foldable Chinese Bluetooth mppt(£40)
As recommended by ut .(Grey with large yellow + - shaped buttons incase anyone interested)
Both been on an hour both charging equally (both up and down as cloud moves)
Tried switching roof panels off..no appreciable difference in folding charge rate and vica Versa
Better results than expected

 

[Nigel Crompton]

Foldable, source, price ?? Please ?
On the cusp of ordering a Renogy 80w (@ €200) folding panel ...

 

[oldiesontour]

Panels eBay 2 x120w total £115 2 months ago.2x stainless steel hinges Screwfix £4 ISH
Mppt Bluetooth controller 40amp Ali express (10 day delivery)£40.
Roof panels were from. same supplier on eBay 2 x 200w a year ago.
Nb just packed folding away..continued as previous post all the way to float charge

 

[oldiesontour]

Folding panels (above bikes

 

[Nigel Crompton]

Folding panels (above bikes



View attachment 876846

Thanks, but I'll be using flexi-panels for ease of manoeuvring & storage

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[oldiesontour]

I researched Flexi they have bad reputation for the material around the panels degrading quickly in sunlight...Think I read Renogy give 5 yr gtee best I could find .You said you were going for 80w ?
You can only expect at very best around 50/60w and that is if you track the sun by keep moving so 5ah 6 hrs day 30ah per day
maybe ok on a good day 3/4ah per day on a dull day at best is this enough also £200 for 80w sounds very expensive ,from memory Renogy were doing 400w for £300 ish

 

[Nigel Crompton]

I researched Flexi they have bad reputation for the material around the panels degrading quickly in sunlight...Think I read Renogy give 5 yr gtee best I could find .You said you were going for 80w ?
You can only expect at very best around 50/60w and that is if you track the sun by keep moving so 5ah 6 hrs day 30ah per day
maybe ok on a good day 3/4ah per day on a dull day at best is this enough also £200 for 80w sounds very expensive ,from memory Renogy were doing 400w for £300 ish

Size isn't everything. I'm 75 with a knackered shoulder (and stuff) managing <2kg is easier than +5kgs.
I've decided a punt on a €70 100w chinese panel off A.es

 

[oldiesontour]

Hope it pays off and does what you hope for