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Adding batteries to an existing battery bank


DeepBass9

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17 hours ago, The Terrible Triplett said:

When I run my house with 6 people off 1 x 1600VA and 1 x 350VA inverter, off grid, I think I would have done well. :D

I am not phased to worry about ovens, stoves, hairdryers, microwaves, vacuum cleaners and such on solar. They use a minuscule amount of watts per month compared to the loads that are needed and on 24/7. 

The ONLY issue I need to resolve on this path ... the kids computers. They need high end computers for the games they play. Note: I rather invest in that power consumption to keep them home, off the road, out of the pubs ... but if Eskom is off, tough ... they can sit and chat with us at the braai. :D

Yes I can go all out and put it all on 5 Axperts with 100 000w panels on the roof ... but I rather spend funds on reducing the load strategically, as they break. Still a while to go for all the stuff to be as economical as it can be. 

Once all is settled, then I add more batteries for the load with 2 days backup, a LOT more panels, and I only have to swap one charge controller with a Victron one like Plonkster has.

EDIT: ok, maybe a controller or two extra. :D

I dunno, the "luxury" of running everything on our house of the 5Kva inverter is just too comfortable for me. we use the stove seldom so I left it on Eskom, but everything else is offgrid during the day. I don't mind building wooden or metal stuff cause all my power tools run off solar. So does the dish washer, microwave, etc, etc. Oh, and my wife's hair dryer and the old power hungry PC ;)

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8 minutes ago, SilverNodashi said:

I dunno, the "luxury" or running everything on our house of the 5Kva inverter is just too comfortable for me. we use the stove seldom so I left it on Eskom, but everything else is offgrid during the day. I don't mind building wooden or metal stuff cause all my power tools run off solar. So does the dish washer, microwave, etc, etc. Oh, and my wife's hair dryer and the old power hungry PC ;)

This I agree with 100%, it's almost no change to your normal lifestyle except for night time

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I run all my power tools from solar too. Except for the welding machine :-) The largest tool (sans welding machine) is a Mitre saw at about 1.2kw. Ye smalle Victron is not phased by it, though it's somewhat close to what could be considered the limit for a 1600va unit.

Perhaps because every power tool supplier thinks it is cool to put numbers up that are bigger than what the device really uses. The mitre saw is more like 900 watts. My wife's hair dryer, marked as 1600W, more like 1300W in real life.

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4 minutes ago, plonkster said:

I run all my power tools from solar too. Except for the welding machine

WHAT, not the welder!!!

No Plonkster, you have no luxury in ye'r bones!

A Voltronix would have been able to run the welder and the rest of the house and cook the food after having done the shopping AND made the beds using only the batteries! :P:P:P

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16 hours ago, Weasel said:

Just a thought here, why not consider diode separation? If you had your load on the back end of a set of diodes coming from each bank they would effectively not see each other. you would have to charge each bank separately and you would have some losses in the diodes. in your case 6kva max load roughly 125A dropping over 0.6 V would mean a max loss of about 75W but i recon under normal loads it will only be around 8W loss. got some nice some nice Schottky diodes for a project the other day that i think could do nicely. you would need at least 8 of them per bank and you'd have to make a chunky PCB.

http://www.vishay.com/docs/94145/16ctq060.pdf

anyone else think this is a viable option?  I think the main issue would be that you wont be able to charge the batts from the inverter.

I think this could work, but this particular diode's pins are a bit thin, IMO. I would expect to use something with much bigger legs for 200A or 400A. Perhaps rather something like this: http://nl.rs-online.com/web/p/rectifier-schottky-diodes/6518608/ And the m8 nut makes it easy to mount in-line as well. 

7 hours ago, Weasel said:

Ah you mean like in some reverse polarity protection circuits, that's certainly doable. now its just a question of it being an issue that the inverter cannot charge the bank.

Well, yea, you'd need to charge each bank separately, which is fine if you use individual components like Morningstar / Outback / Vicron / etc. 

 

The bigger question is, what impact will this have on the batteries. 

Let's say you draw 2000W. Now if one bank sits on 51.2V and the other on 52.8V, will the banks each deliver exactly 1000W? Probably not. In theory, both batteries will equalize at 51.2V and should then deliver 1000W @ 19.53125A. BUT will this still be the same with the schottky diode's in place?

The fuller battery bank will always be fuller though and you might deplete the old set quicker if it eve goes to 50% of the fuller bank. Theoretically it shouldn't since the emptier bank will supply the reference voltage. 

It would be fun to setup something like this though and see exactly what happens. 

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59 minutes ago, DeepBass9 said:

I run my welder from my inverter, but only at around midday, What voltage is a cheap inverter welder? I usually have it on 90-120 Amps. It seems to draw about 3Kw while welding.

I have an old "oil bath" and a new inverter TIG welder, but running on the Axpert 5Kva without issues but I don't know how many Watts they use since I can't weld and check the inverter. Generally the new cheaper inverter welders step down to 24 or 36V on the DC side

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22 minutes ago, The Terrible Triplett said:

A Voltronix would have been able to run the welder and the rest of the house and cook the food after having done the shopping AND made the beds using only the batteries! :P:P:P

Ah I forgot you have to size your panels to your batts for the boys in blue and maybe that's why TTT tends to forget you can use just panels during the day

54 minutes ago, SilverNodashi said:

offgrid during the day

 

46 minutes ago, viper_za said:

almost no change to your normal lifestyle except for night time

Must be the blue tunnel vision missing these words ;)

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@SilverNodashi and @viper_za

You can buy a truck to move a load that a old blue Nissan bakkie can do - without breaking a sweat.

For me "luxury" would be to reduce my footprint to as small as it can be without losing the 'comforts' ... as cost effectively as I can.

And if I can do it all with low cost 2nd hand equipment, MAN, now THAT is sommer seriously "luxurious".

After having bought new all my life ... new being till you drive it off the show floor, or a panel being mounted gets that 1st scratch ... when you hit that 2nd hand part at a real bargain ... nothing beats that when it works for many many years. And if it breaks, so what, it was 2nd hand, get another one.

But hey, each to our own devices ne.

 

:D:D:D and that brings me to this point.

I will either wait very patiently for you guys to start replacing your Voltronics for newer, better, bigger models... offering you R500 bucks for yours, for there will be a lot available then.

A lot available, what, is he crazy? 

Nope. Saw this pattern the last few years with UPS'es.

There is a massive amount of owners out there having bought Voltronic devices due to power failures.

Most have insufficient batteries, insufficient panels or using the wrong settings not understanding SOC AND whom have not discovered this forum yet!!!

So, when the next round of power outages hit, they will most probably have to replace their battery banks.

And that is when most call it a day, resulting in a lot of Voltronic devices coming onto the market then. :P

Then I have a Victron AND a few cheaper than cheap Voltronics devices to weld with - vir 'n appel en 'n ui. :D

 

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1 hour ago, The Terrible Triplett said:

@SilverNodashi and @viper_za

You can buy a truck to move a load that a old blue Nissan bakkie can do - without breaking a sweat.

For me "luxury" would be to reduce my footprint to as small as it can be without losing the 'comforts' ... as cost effectively as I can.

And if I can do it all with low cost 2nd hand equipment, MAN, now THAT is sommer seriously "luxurious".

After having bought new all my life ... new being till you drive it off the show floor, or a panel being mounted gets that 1st scratch ... when you hit that 2nd hand part at a real bargain ... nothing beats that when it works for many many years. And if it breaks, so what, it was 2nd hand, get another one.

But hey, each to our own devices ne.

 

:D:D:D and that brings me to this point.

I will either wait very patiently for you guys to start replacing your Voltronics for newer, better, bigger models... offering you R500 bucks for yours, for there will be a lot available then.

A lot available, what, is he crazy? 

Nope. Saw this pattern the last few years with UPS'es.

There is a massive amount of owners out there having bought Voltronic devices due to power failures.

Most have insufficient batteries, insufficient panels or using the wrong settings not understanding SOC AND whom have not discovered this forum yet!!!

So, when the next round of power outages hit, they will most probably have to replace their battery banks.

And that is when most call it a day, resulting in a lot of Voltronic devices coming onto the market then. :P

Then I have a Victron AND a few cheaper than cheap Voltronics devices to weld with - vir 'n appel en 'n ui. :D

 

But my 10Ton truck will do the trip once while you probably have todo the same trip 14 times!

I hear what you're saying about the cheap Victron's. Most people have that negative feeling about, and it's understandable. But the more expensive inverters also break down at some stage and need to be replaced. 

On the flip-side though, people don't use the wrong batteries / panels / settings just cause they use Voltronics. They use the wrong equipment and settings cause they dealt with fly-by-night resellers who don't understand this either, regardless of what they were prepared to pay for their kit. A Victron on the wall doesn't mean you will automatically use proper expensive batteries, on the contrary you would probably very well still be using cheap deep cycle batteries with 700 cycles!

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small pins wouldn't be an issue if there are many but i like the look of that one, it would cost around 600 bucks here which is more or less what a assembly of small ones would work out to be, so agreed this is a better easier option..

12 minutes ago, SilverNodashi said:

The bigger question is, what impact will this have on the batteries. 

Let's say you draw 2000W. Now if one bank sits on 51.2V and the other on 52.8V, will the banks each deliver exactly 1000W? Probably not. In theory, both batteries will equalize at 51.2V and should then deliver 1000W @ 19.53125A. BUT will this still be the same with the schottky diode's in place?

The fuller battery bank will always be fuller though and you might deplete the old set quicker if it eve goes to 50% of the fuller bank. Theoretically it shouldn't since the emptier bank will supply the reference voltage. 

The bank with the least internal resistance will supply the most current so that would mean the one with the most charge and/or the one which is the newest.  you are technically correct but i don't necessarily agree. its a theory and practice kind of thing because the fuller bank always being fuller would depend more on how each bank is charged. The newer bank would work a little and i do mean "a little"  harder on a discharge only, and only if they are exactly equally full. The way I see it the system would self balance quite nicely and the problems are really with charging. 

i've got enough crap lying around to test such a setup but time is the real problem.<_<  

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oh and one other point being that by having diodes in place will rather serve to equalize current draw from each bank because it inhibits current "more equally" (yes its a thing :)) where when having two in parallel one could be doing far more because it has half the IR resulting in a larger difference. The v drop could therefore be good thing

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Re Diode discussion. When you place batteries in parallel, they are forced to work at the same voltage. Whatever battery has the most capacity will deliver the bulk of the current, so what you find is that each battery/bank will deliver according to its capacity. The experiment has been done and a paper was written.

http://neuralfibre.com/paul/wp-content/uploads/2007/05/can-we-now-sin.pdf

The moment you have a diode or even a MOSFET in there, all bets are off. It would be better to use 19th century tech for this: a Relay!

All of this assumes your parallel strings use the same chemistry.

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1 hour ago, Weasel said:

small pins wouldn't be an issue if there are many but i like the look of that one, it would cost around 600 bucks here which is more or less what a assembly of small ones would work out to be, so agreed this is a better easier option..

The bank with the least internal resistance will supply the most current so that would mean the one with the most charge and/or the one which is the newest.  you are technically correct but i don't necessarily agree. its a theory and practice kind of thing because the fuller bank always being fuller would depend more on how each bank is charged. The newer bank would work a little and i do mean "a little"  harder on a discharge only, and only if they are exactly equally full. The way I see it the system would self balance quite nicely and the problems are really with charging. 

i've got enough crap lying around to test such a setup but time is the real problem.<_<  

well, that's the thing, it's all theoretical based on ohm's laws and calculations. Since the Volts will be equal, and the Kw drawn is predetermined (even if it changes the whole time) in theory they should both serve the same current (Ampere). 

w.r.t charging, even if you have the same charge setup, whether it's a AC/DC charger, or a PV array, the batteries will charge differently due to their chemistry inside, and thus you would have two imbalanced battery banks. 

I'm just curious how this would work out in the long run, i.e. would the new bank last as long as it could have if it was a standalone system?

 

I actually have some time for an experiment like this but don't have an old and new battery bank of the same make / model, nor enough data logging equipment to carry this out. 

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3 minutes ago, SilverNodashi said:

I'm just curious how this would work out in the long run, i.e. would the new bank last as long as it could have if it was a standalone system?

If someone is willing to sponsor me with 16 new T105-REs I will perform the tests over the next 5 to 10 years and then report back.

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1 hour ago, plonkster said:

Re Diode discussion. When you place batteries in parallel, they are forced to work at the same voltage. Whatever battery has the most capacity will deliver the bulk of the current, so what you find is that each battery/bank will deliver according to its capacity. The experiment has been done and a paper was written.

http://neuralfibre.com/paul/wp-content/uploads/2007/05/can-we-now-sin.pdf

The moment you have a diode or even a MOSFET in there, all bets are off. It would be better to use 19th century tech for this: a Relay!

All of this assumes your parallel strings use the same chemistry.

Their test wasn't done with diodes as is being discussed here, hence the results they got. 

My theory is that since the diodes block off each battery bank, neither bank would know what the other bank has in possession. Ohm's law still dictates that the voltages would be equalized and I suspect that since we're drawing a fixed wattage from the combined setup, each bank will deliver the same Ampere at the same Volt. The one bank will probably just get depleted before the other one could, and thus "drain" the whole setup quicker than two new bank would have. 

i.e. two new banks of 54V, 10A would deliver 540Kw/h, or 9Kw in 1hour. 

one set of 52V, 10A and one set of 54V, 10A would equalize @ 52V, and thus deliver 8.7Kw in 1 hour, or 9Kw in 57.8 minutes

I'm not taking pheukert's law into account, purely to keep the math simple.

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1 hour ago, Chris Hobson said:

I like welding with my inverter. I get a much better weld than with my old petrol Roughneck welder. I always thought I was a crap welder but I can make a very neat weld with inverter powered inverter welder.

haha, I also thought I was a crap welder but then realized my old oil bath is just that old...

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1 hour ago, superdiy said:

If someone is willing to sponsor me with 16 new T105-REs I will perform the tests over the next 5 to 10 years and then report back.

yea, the cost of R&D is generally much more than producing the actual product ;)

Surely you could do the same test on a 12V or 24V system as well?

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14 minutes ago, Chris Hobson said:

I like welding with my inverter. I get a much better weld than with my old petrol Roughneck welder. I always thought I was a crap welder but I can make a very neat weld with inverter powered inverter welder.

Time to redo the frame of the panels. :D

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Problem is that neither a silicon diode (with a fairly constant drop) nor Schottkys or MOSFETs have a constant drop, it always depends on the current, and with dissimilar strings the current is going to be different, so the extra component in the system will either make it better or worse, depending on how you have it arranged. If you hard-latch them together, you get the behaviour as described in the paper linked above. The batteries themselves dictate how much current each contributes, according to their age and capacities.

It is this "surprising" result that I would like to piggy-back on. I say surprising because even today you hear people argue that "parallel is bad because of circulating currents", and that is simply not true. You connect them together, charge from the higher side moves to the other side until their voltages are the same, and then the electrons stop moving. No potential difference to make them move. When you apply a load, whichever battery has the most ability to move electrons moves the most electrons, so you get a natural division of work.

By tomorrow morning both banks should be at roughly the same DoD. Now you simply charge them separately to avoid the overcharge/undercharge problem, because they are not as helpful in "naturally" distributing charge! :-)

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8 minutes ago, SilverNodashi said:

haha, I also thought I was a crap welder but then realized my old oil bath is just that old...

I have a transformer welder with a fan. It isn't significantly different to the oil-bath type. I found that the kind of rod I use makes a big difference. I used the builders-warehouse special for a while, and all the while I was thinking... man... I need more practice... I am SUCH a poor welder. Ran out of rods, went back to buy more... all they had was Afrox Vitemax. Expensive, but bought them anyway. What a difference!

So moral of that story: Either get a proper welder, or use better rods. Poor welder with cheap rods = frustration.

Edit: Mattweld. That was the brand I used before switching to Vitemax.

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