Victron Battery Balancer, Mk2 USB,702 and 24V inverter

[Camel]

Right guys I have be following:

13 by Battery Balancer R700 each (New) (7 left)

1 by MK2 USB R650 (New)

2 by 24v 1450va Inverter (Not sure of a price but need it gone as it is collecting dust) (second hand)

1 by 702 R2400 (New)

Happy shopping

Edited October 10, 2016 by Camel

[Camel]

[Camel]

right guys I need to clear stock. I have the following deals

13 by Battery Balancer R550 each (New) (5 left)

1 by MK2 USB R500 (New)

Cheers

[Guest]

How many batteries can the Vectron balance?

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[Camel]

All depends on what system you have. 

https://www.victronenergy.com/battery-monitors/battery-balancer

[Guest]

Have 4 batteriea 24volt

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[___]

As far as I know the Victron balancers balance two halves. So if you have a 24V system with two 12V batteries, you will need one balancer. For a 48V system you'd need 3, to illustrate, suppose you have 4 12V batteries numbered 1 to 4, you'd balance them in pairs 1 and 2, 2 and 3, 3 and 4.

It only works across 12V "halves", so with 6V batteries you'll still need 1 (for a 24V system) or 3 (for 48V).

You could also use 5 to balance:

1. Balance 1+2 with 3+4

2. Balance 2+3 with 4+5

3. Balance 3+4 with 5+6

4. Balance 4+5 with 6+7

5. Balance 5+6 with 7+8

But at this point things start to become very messy and expensive :-)

https://www.victronenergy.com/upload/documents/Datasheet-Battery-Balancer-EN.pdf

[Guest]

Thank you plonkster. Appreciate it

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[Jaco De Jongh]

On 2016/11/08 at 9:23 AM, plonkster said:

So if you have a 24V system with two 12V batteries, you will need one balancer.

I need to assist with an installation of battery balancers.  the setup looks similar to the diagram below, but with 1 added parallel string, making it a total of 8 batteries.

The person I need to help with the installation feels that in a situation like this, 2x battery balancers will be better than 1.

My Question: With the 702 already installed, the  + / mid / - points were already created, will a second unit benefit this setup at all? If so, how to connect the second one? The only logical connection if it is at all possible is a parallel connection, but i can not see the benefit of doing so.

@Camel, @plonkster, please advice, I am playing with new toys here and not sure what to think. I did search on the victron site but could not find anything related to such a connection.

 

[___]

Weeelllll.... if you want to use two balancers, then you simply link the midpoints in two places so that you have two pairs rather than linking all 4. But if you do that then the BMV can obviously only monitor the midpoint on one of the two.

[superdiy]

58 minutes ago, plonkster said:

Weeelllll.... if you want to use two balancers, then you simply link the midpoints in two places so that you have two pairs rather than linking all 4. But if you do that then the BMV can obviously only monitor the midpoint on one of the two.

The Victron balancer only balances at up to 0,7A, so adding more in parallel, should increase the balancing current and rate. As per the datasheet they can be operated in parallel. 

Besides the fact that it is a bad idea to have parallel strings in the first place, it is even worse to link any of the batteries within strings together, not even midpoints, because if one cell in one battery fails and shorts, the drop in voltage will be absorbed by all the batteries in the string and the fault current will be much less than when some or all the batteries or midpoints are linked, because then only one battery will have to absorb the voltage drop if a cell in a parallel battery fails. The fault currents will be higher if the number of cells per battery is lower and if you connect 2V cells in parallel and one of them fails, just imagine what the other parallel cells will try to do and what amounts of current will flow.

So if you can avoid it, never connect battery strings in parallel, if you have no other option, add a serial fuse per string (discussion somewhere else on the forum) and never connect / link batteries in parallel strings directly - if you have to, in order to do balancing or to monitor the midpoint, then add fuses between the points where you tie the batteries, as per the diagram below - almost as if you are adding more bus-bars and fuses to each string connected to the bus-bars.

Please note - parallel battery strings:

• Keep the total length of cable per string equal and use the same wire gauge in each string, preferably terminated onto bus-bars for positive and negative.
• If you are tying midpoints, for example, ensure that the total cable length between the midpoint and the positive bus-bar needs to be the same as the total cable length between the midpoint and the negative bus-bar, otherwise you will also create an unbalanced system with unbalanced batteries and even with a battery balancer installed, it will continuously try to balance the batteries without success - again refer to the diagram below and note that the total cable length on each string on each side of the midpoint is equal and that the midpoints are connected via fuses to a midpoint (bus-bar) e.g. for BMV midpoint connection.

If you are only monitoring the midpoint, e.g. with a BMV, then use fuses with low ratings, e.g. 5A. If you are making use of battery balancers, adjust the fuse ratings of the midpoint fuses according to the balancer used, e.g. the HA02 balances at up to 10A, so add 15A fuses.

The Victron battery balancer balances at up to 0,7A, so the 5A fuses should be fine.

[Jaco De Jongh]

1 hour ago, plonkster said:

then you simply link the midpoints in two places so that you have two pairs rather than linking all 4. But if you do that then the BMV can obviously only monitor the midpoint on one of the two.

That is exactly what i was afraid of, and from there the question if it will be beneficial to add a second unit unto a system with an already installed 702 and an established midpoint. 

2 hours ago, Jaco de Jongh said:

The only logical connection if it is at all possible is a parallel connection, but i can not see the benefit of doing so.

Thanks @superdiy for supplying the clarity.

1 hour ago, superdiy said:

As per the datasheet they can be operated in parallel. 

I only saw that part now after you mentioned it.

1 hour ago, superdiy said:

if you have no other option, add a serial fuse per string (discussion somewhere else on the forum) and never connect / link batteries in parallel strings directly

As for the above, this is new to me, but surely worth looking into, for my own bank and for others that I try to help. Thanks.

[Chris Hobson]

Hi Jaco I am not sure I understand. You have Infinisolar V series which is 48V and then you need 3 balancers (which you have) and then you have a 12V system which can be balanced with a HA02 if you have 6V batteries but not with a Victron battery balancer which expects 24V across its terminals (actually up to 36V but lets not get sidetracked). Are you balancing a 24V system? If so ignore my post. 

[Jaco De Jongh]

1 hour ago, Chris Hobson said:

Hi Jaco I am not sure I understand

Hi Chris, this is not for me, its for a friends installation. He bought 2 balancers for his 24volt bank, I have to help him install them tomorrow, just wanted to make sure i understand the connection correct before I do something stupid, resulting in me having to replace something.

[Mark]

Hi Jaco

There was a long debate about using one balancer for 2 strings... I have gone that route but have fused (5a automotive) each of the positive (red) links between the 2 strings.  I extended the wire... I have been using it like this for months and have had no issues... 

Regard

Mark

[superdiy]

2 hours ago, Mark said:

Hi Jaco

There was a long debate about using one balancer for 2 strings... I have gone that route but have fused (5a automotive) each of the positive (red) links between the 2 strings.  I extended the wire... I have been using it like this for months and have had no issues... 

Regard

Mark

I cannot see any fuses in your diagram above, so if it is connected as per the diagram, you have batteries connected in parallel and although it will work fine under normal conditions, you will have serious issues when one cell in one of the batteries fail (goes shorted), as per my explanation a few posts up.

From my own experience I had a failed cell in a 48V string and the battery with the failed cell as well as the other batteries in that string was too hot too touch when I discovered there was a problem. The remaining 23 cells in the string absorbed the "over voltage" applied by the other parallel strings and maintained by the charge controller. Now say the total voltage for the string was 48V, that is 2.0V per cell, now, with one cell shorted in the string, the voltage per cell is raised to 2.09V (less than 5% increase), which is not too much of a difference. Now in your case you have 12V batteries in parallel, so when 1 cell fails the voltage per cell goes from the nominal 2V to 2.4V (20% increase) which will result in much higher fault currents and much more heat and and and.  Let's take it a step further, if you have 6V batteries in parallel and one cell fails, the voltage in the remaining cells will rise from 2V to 3V (50% increase) - I don't even want to think what would happen if you connect 2V cells in parallel and one of them fail.

Bottom line, as long as the cells are fine, everything will work fine, but if you do not link the batteries via fuses and a cell fails, you might loose not only the battery or the battery bank, but the surroundings (house) as well. When I still had parallel strings (not batteries) I disconnected all except one parallel string whenever we went away for more than a day, just in case something went wrong in a parallel string and it was discovered too late.

[superdiy]

3 hours ago, Mark said:

I have gone that route but have fused (5a automotive) each of the positive (red) links between the 2 strings. 

5A fuses used in conjunction with the HA02 might result in nuisance blowing problems if your bank is very unbalanced, because according to the HA02 specs they can balance at up to 10A, obviously the current will be lower if the bank is more balanced. I would rather suggest a 15A fuse which would prevent nuisance blowing, but still protect everything in case a cell goes shorted.

[Mark]

I have had no fuses blow and would rather be safe... my bank is seldom out of balance by more than 0.5% and normally 0.1%.

So no - no 15a fuses for me... 

 

[Jaco De Jongh]

On 2016/11/23 at 3:09 PM, superdiy said:

add a serial fuse per string

Hi SuperDiy, would you mind posting a picture of the type of fuse holder you prefer to use, maybe if you have done it before, a picture of such a connection.

Would really appreciate it.

[superdiy]

14 hours ago, Jaco de Jongh said:

Hi SuperDiy, would you mind posting a picture of the type of fuse holder you prefer to use, maybe if you have done it before, a picture of such a connection.

Would really appreciate it.

That was still in the early days, a few years ago. I've used automotive "bolt down fuses", but you should not use those because they are only rated for up to 32V.

 

[Jaco De Jongh]

13 minutes ago, superdiy said:

That was still in the early days

Thanks super.

On 2016/11/24 at 6:17 AM, Mark said:

I have gone that route but have fused (5a automotive)

Mark do you mind sharing a photo of one of your connection? I am just gathering some ideas.

[superdiy]

Hi Jaco, you can always use something like these inline type fuse holders to link battery midpoints or for the connections to the battery balancers. They accept standard 20mm and 25 mm fuses rated at 250V and they are quite cheap and freely available.

[Mark]

Looks something like this. ..

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[superdiy]

On 11/25/2016 at 10:49 AM, Mark said:

Looks something like this. ..

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Those are used for automotive blade fuses rated at 32V only, so unless you are using them in a 12V or 24V system, don't use them.

 

http://za.rs-online.com/web/p/automotive-fuses/7874126/

 

[Mark]

I think the point is missed here. They are being used for the ha02 connections between banks for balancing only.... so max of 12v or 10a.

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