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Stephan

Battery Balancer/Monitor

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On 2017/04/30 at 10:06 PM, pilotfish said:

Add additional battery bank to give you around 8 hours at 20-30% DoD,

Hallo Pilotfish

Quick question: I am in the process to purchase another 2x batteries as you suggested. I currently have the 2x Narada 200ah AGM batteries. Can I get for example 2x trojan batteries as long as they are AGM? And must it match the AH of the other two batteries or can it for example be 2x185ah?

Thanx

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11 hours ago, Stephan said:

Quick question:

Hi Stephan, the common advice is as follows;

  • Never mix new with used (75% agree, to me this would depend on circumstances),
  • never mix sizes (100% agree),
  • never mix chemistry (100% agree),
  • never mix manufacturer (95% agree).

The quickest path to destroying a bank of batteries is charge imbalance. If you have 4 similar batteries, all with no manufacture defects and a good battery balancer, then the imbalance which will come about can be evened out by the battery balancer and you have the best chance of longevity.

If you have a mixed bag of batteries with differing charge/discharge rates then the battery balancer is unlikely to be able to do its job and your batteries will quickly be toast.

Even similar chemistry (AGM for instance) from different manufacturer will more than likely have differing construction methods resulting in charge/discharge disparity.

In your case with what I understand to be relatively fresh batteries I would weigh up my options depending on circumstances (hence the 75% agree),

  • If you find that your discharge rate is 50% or less on your current battery bank then maybe use as is until kaput, then replace with batteries more suited to high cycle operation (I think your batteries are good for standby use, but not great for daily cycling),
  • If your current discharge rate is in excess of 50% then get 2 more of the identical battery and hope for the best - again use until they have had it then replace with something more suited to high cycling.

Option 1 would be my preferred option if I was in your shoes, I would hate to throw away the money already spent on existing bank but also loathe to spend more on batteries not really suited to the task.

Other opinions may differ!

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You should never mix batteries from different manufacturers or of different models or of different Ah ratings or of different ages or of different chemistries. 

Even more, to add parallel battery strings (more batteries) is also challenging in many ways and if that is the only option, it should be done correctly - refer to my guide for more information regarding parallel battery strings: 

If you are thinking of increasing the capacity of your battery bank, rather buy new batteries of higher Ah ratings and ensure that you end up with only 1 string of batteries. 

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1 minute ago, pilotfish said:

Option 1 would be my preferred option if I was in your shoes,

Agreed. Get 2 more Naradas. Then what I would do is make up two strings with one old and one new battery in series, and then put balancers across them. My reasoning is that this is the most reliable way to get two strings with roughly the same internal resistance, so that the charge current is shared roughly 50/50 between the two strings. If you do it the other way (new string in parallel), one bank will overcharge and the other will undercharge and there is no way to fix this with a balancer.

The balancers should sort out the imbalance that will be created by the mixed series string and ensure that both batteries get a good charge. If they aren't too badly mismatched of course, I'd say under 6 months it should be fine.

Make no mistake, you will still shorten the life of both the old and the new batteries, but it might be an acceptable cost compared to the alternative (which is to swing them and buy bigger batteries).

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On 5/2/2017 at 6:34 PM, Camel said:

 

Talking about monitoring batteries,look what arrived today

 

Hey I got some of those , quite lekker to have a quick reference when walking into the batt room :) 

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2 hours ago, pilotfish said:

Other opinions may differ!

.... but they are wrong :D - so we will take Pilotfish's recommendation. Plonky suggestion is very workable but even he concedes is going to shorten battery life but gives you more capacity for a smaller negative trade-off.

 

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4 hours ago, pilotfish said:

Option 1 would be my preferred option if I was in your shoes, I would hate to throw away the money already spent on existing bank but also loathe to spend more on batteries not really suited to the task.

Hallo Pilotfish

Thank you for the great feedback. From what I found on the internet I saw that it is never to mix anything else than exactly the same of everything.

I suppose its called the "battery race" :)

Since you have mentioned that Naradas are better for backup batteries, I would prefer to use-up the 2x200ah and then buy new sets of Trojans. That is of course if I do not discharge them more than 50% per cycle. The batteries are still new, so it would not be an issue to buy 2 extra should my load be too much.

I received my HA-02 already and awaiting my BMV702. Once set up, I will exactly calculate my loads to determine which route I might have to go eventually.

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2 hours ago, Chris Hobson said:

.... but they are wrong :D - so we will take Pilotfish's recommendation. Plonky suggestion is very workable but even he concedes is going to shorten battery life but gives you more capacity for a smaller negative trade-off.

 

Though @plonkster's idea actually makes a lot of sense. Running a new and old battery in series, per string, should balance the charge and discharge quite a bit. But you'll probably still get some excesive heat between the old and new battery and higher discharges?

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1 minute ago, SilverNodashi said:

some excesive heat between the old and new battery and higher

Depends on the age. If the one battery is significantly worse off than the other one, then the good one has to pass all its current through the bad one next to it (the one with the higher internal resistance), so all sorts of bad things will happen. Your midpoint will also drift during hard discharges. IF the batteries are just mildly mismatched, the weaker battery determines the available discharge current (that is good) and the balancer works a bit harder to ensure that the new battery (with the lower internal resistance) is properly brought up to absorption voltage and gets a full charge.

Full of caveats as always.

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13 minutes ago, plonkster said:

Depends on the age. If the one battery is significantly worse off than the other one, then the good one has to pass all its current through the bad one next to it (the one with the higher internal resistance), so all sorts of bad things will happen. Your midpoint will also drift during hard discharges. IF the batteries are just mildly mismatched, the weaker battery determines the available discharge current (that is good) and the balancer works a bit harder to ensure that the new battery (with the lower internal resistance) is properly brought up to absorption voltage and gets a full charge.

Full of caveats as always.

And that's the problem, you won't really know how well, or bad this design could work, until you try it in real life. 

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27 minutes ago, SilverNodashi said:

And that's the problem, you won't really know how well, or bad this design could work, until you try it in real life. 

So for a low cost risk like this one (<5k?) might be worth it. Would not do it with a 40k+ bank :-)

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Ok, now I have everything connected to start fitting all devices and appliances. Two questions though:

1) There is a slight high pitch sound coming from the batteries- Is this normal? (2x 200ah Narada AGM)

2) My 3000w Devel inverter is pulling 95w? Is this acceptable? 

Thanx

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The high pitch sound is coming from the HA02. Mine does this as well, apparently it is normal. Its more noticable for me in the morning, I guess that batteries go out of balance overnight?

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3 hours ago, Stephan said:

Ok, now I have everything connected to start fitting all devices and appliances. Two questions though:

1) There is a slight high pitch sound coming from the batteries- Is this normal? (2x 200ah Narada AGM)

2) My 3000w Devel inverter is pulling 95w? Is this acceptable? 

Thanx

My 3x4KW Axperts consume 105W!

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95w is not really acceptable, but when I switch on the the fridge it only goes up in TOTAL to between 115-160w depending on the fridge load. So I suppose when it is in idle it uses a bit more in comparison to when it is operating. Not sure whether its possible/right!? But that seems to be the case.

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2 hours ago, Stephan said:

So I suppose when it is in idle it uses a bit more in comparison to when it is operating

Inverters also have a base load, the amount of power it draws just to keep everything humming. This overhead usually does not decrease with load, rather it increases as things get hotter and fans pick up speed. At least, such is my experience with my own equipment, the 18w it needs just to keep ticking is always there, but it can increase to over 100W of overhead when running full-tilt, which is still just 8% of the overall power equating to an efficiency of 92%... but enough to be noticeable.

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22 hours ago, Stephan said:

95w is not really acceptable, but when I switch on the the fridge it only goes up in TOTAL to between 115-160w depending on the fridge load. So I suppose when it is in idle it uses a bit more in comparison to when it is operating. Not sure whether its possible/right!? But that seems to be the case.

What did you use o measure the consumption with?  Does your meter / measuring device take power factor into account or are you actually measuring VA and not W?

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Hi Stephan,

14 hours ago, superdiy said:

Does your meter / measuring device take power factor into account or are you actually measuring VA and not W?

My understanding is that the equipment is intended for an "off grid" role in a coffee vending trailer, so I would assume that the 95W load mentioned is a DC measurement on the battery side while no AC input is connected, in which case power factor would not come into it.

I see from the net that your inverter weighs in at 24kg, which tells me that it incorporates a high power transformer as apposed to other designs which are all electronic.The up side of your system type is that in general they are very hardy and can withstand high surges without sustaining damage (as evidenced by the quoted 9kw surge tolerance), the down side is that they are pretty inefficient with high magnetizing current required to power up the monster transformer.

Your inverter would be better suited to a standby role where it has a constant supply and is required to supply varying loads for short term power outage, but you can still use it in your required role as long as you know about the overhead and provide for it.

I believe your best solution is to install the complete system and run it in the back yard for a day or 2 to measure battery drain and then decide if you are good to go or require additional battery capacity. At 45amps your charger could handle a 400Ah battery bank without too much sweat.

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17 hours ago, pilotfish said:

I see from the net that your inverter weighs in at 24kg, which tells me that it incorporates a high power transformer as apposed to other designs which are all electronic.The up side of your system type is that in general they are very hardy and can withstand high surges without sustaining damage (as evidenced by the quoted 9kw surge tolerance), the down side is that they are pretty inefficient with high magnetizing current required to power up the monster transformer.

Man, some days I'm glad I do my homework rather than shooting from the hip. I was about to tell you that 24kg isn't that much, the 3kva multi comes in at around 18kg for example, and even though it has a heavy toroidal transformer (which is a good thing), it is a high-frequency design.

But, as I said, I did my homework, and I found that this inverter is also sold under the name Cosuper. And someone opened it up and snooped inside, and here you can clearly see the big old iron transformer.

Now the size of the transformer does not in itself translate to better or worse efficiency. A transformer is designed to operate at a particular frequency and if you do it properly, the efficiency can be pretty high. The "electronic type" uses a higher frequency and a smaller core, but overall transformers of all kinds are still some of the most efficient devices out there despite their age. There is however a problem with a large core transformer with no load on the secondary side: High core losses, due to hysteresis loss which is proportional to the volume of material in the core, and that perhaps explain why this inverter is advertised as having an efficiency of 88%. Given that manufacturers generally publish the best number obtained (at a nice steady linear load), I suppose one just has to accept that this is an "old school" inverter.

Now that I know it has a big iron transformer, perhaps it makes sense that the "overhead" does drop slightly as you put load on. Your hysteresis loss is lower when you have a load on the output, some of that magnetism is removed from the core (by the load on the secondary) and so less energy is spent reversing the magnetization.

That's also why large transformers with small loads have such a horrific power factor. It's essentially swinging a magnetic field around and since that thing has some "weight" to it (in the proverbial sense) it always lags behind.

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