Guest Posted July 22, 2016 Share Posted July 22, 2016 I want to ask on a little matter that I am not always 100% clear on. 2250w array 150v 70amps MPPT - separate 3000va inverter - separate 225ah Battery bank Using a 70amp controller I can get a 700ah bank using the 10% charge rate. Question: To use the 2.25kw array to its full potential, I add loads to run array at max. But this may result in 70amps going thought the system, most used by inverter yes. But is there not a standard formula between max array size for battery bank max size? Quote Link to comment Share on other sites More sharing options...
DeepBass9 Posted July 22, 2016 Share Posted July 22, 2016 As I understand it the 70A is max the battery charging amps, so 48V x 70A = 3.36kW which is much bigger than your array so no problem. I have a 60A MPPT so am limited to 3kW. Quote Link to comment Share on other sites More sharing options...
Guest Posted July 22, 2016 Share Posted July 22, 2016 70amp the max the controller can handle yes. Sorry, I forgot to add: 24v On a 225ah battery bank I should limit the controller to max 23amps, but then if I have a 2.25kW array, am I not losing out on the large array? With a Axpert you can set the battery charging and if there is more power needed, the Axpert can pull more amps from the panels without affecting the max battery charge setting I am told. Very cool feature. But how will it work with separate controller I wonder? Quote Link to comment Share on other sites More sharing options...
Louw Posted July 22, 2016 Share Posted July 22, 2016 I would go with (70A Plus Base Load) / 14% (Maximum charge current for T105) i.e Base Load of 240w = 10A (70A + 10A)/14% = 571AH Quote Link to comment Share on other sites More sharing options...
DeepBass9 Posted July 22, 2016 Share Posted July 22, 2016 What's the 14%? VAT? I have struggled to find the maximum recommended charge current for my T1275s. Empirically it is probably about 80A which is where they start behaving strangely and warming up if I charge from a generator (single string). Quote Link to comment Share on other sites More sharing options...
Arandoza Posted August 21, 2016 Share Posted August 21, 2016 What's the 14%? VAT? [emoji14] I have struggled to find the maximum recommended charge current for my T1275s. Empirically it is probably about 80A which is where they start behaving strangely and warming up if I charge from a generator (single string). Deepbase9 if you are pushing 80amps into your battery bank I trust it's a 800ah bank or thereabouts ? Everything on the forums I have seen suggests never to exceed around 13% of your amp hour rating. In my case battery bank c20 rating 245ah, so charge rate could be 20-30 amps, as mine can only be set in Increments of 10amp, so 2amps, 10,20,30,40,50,60max on the Axpert. Hope you haven't been overcharging the batts? Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted August 21, 2016 Share Posted August 21, 2016 AGM batteries can handle a charge considerably higher up to C/5 for 2 hrs. So I can charge my 260 Ah system at 50A (for 2 hrs) and then 26A for 7 hrs. I normally charge at 30A. I would dearly love to have a bank twice the size as then I could really open the taps. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 Yes, lead acid and AGM's have different charge settings and rules. I.e. AGM's must never be equalized, ever. Lead acid should be equalized at least once a month - but be aware of the higher volts at the time. It can cause an issue with equipment. Yes, I have the T-shirt for that too. On lead acid, do not exceed the 13% rule on charging amps. You will break them and a good supplier can see that you over charged / under charged the bank. And not below 10% either. Below 10% there are T&C like the batts are purely there for backup and can take days to recharge if you charge at say 8%. It is good to recharge batts every day but if it takes a week to re-charge due to weather, that is fine as long as you don't go below 50% in that time. But then, even if you do go once in a long while below 50%, it is not that big an issue. Doing it regularly is very bad, then get more batteries. Remember: Batteries are more expensive than Eskom. Batteries are cheaper than a generator. EDIT: As per Viper's post below, THE best way to determine if equalization is required, is to measure each cell with a hydrometer. Invest in a hydrometer, measure each cells gravity and note the readings for future comparison. Quote Link to comment Share on other sites More sharing options...
viper_za Posted August 22, 2016 Share Posted August 22, 2016 51 minutes ago, The Terrible Triplett said: Lead acid should be equalized at least once a month - but be aware of the higher volts at the time. It can cause an issue with equipment. Yes, I have the T-shirt for that too. Just a quote direct from the Trojan website "Many experts recommend that batteries be equalized periodically, ranging anywhere from once a month to once or twice per year. However, Trojan only recommends equalizing when low or wide ranging specific gravity (>0.030) are detected after fully charging a battery."http://www.trojanbattery.com/tech-support/battery-maintenance/ If I look at my system, batteries being discharged to +-80% SOC every night (70% deepest yet) for almost 8 months now. Keeping in mind that I have never equalized my bank before. Coincidentally I took gravity readings yesterday just before PV stops producing(bank 100%) yielded better readings than what Trojan recommends they should be at. I'm not saying you don't have to equalize but when you look after your batts you can get away without doing it that much. Chris Hobson 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 YES!!! What you said above Viper, is absolutely the best advice. Everyone should have hydrometers and should check the batts as you say. From today we should ask: Do you have a hydrometer? Yes, right, check the readings and record them and if out of whack, then equalise. Have altered my post above to reflect same. Quote Link to comment Share on other sites More sharing options...
___ Posted August 22, 2016 Share Posted August 22, 2016 1 hour ago, The Terrible Triplett said: On lead acid, do not exceed the 13% rule on charging amps I believe 13% is the recommended rate for off-grid usage. You can go up to 15%, but efficiency suffers a bit, and up to 20% for short periods. So it's a bit like that road I drive to work every morning... limited to 100km/h, recommended 80km/h (because of all the potholes). Quote Link to comment Share on other sites More sharing options...
SilverNodashi Posted August 22, 2016 Share Posted August 22, 2016 Just now, The Terrible Triplett said: YES!!! What you said above Viper, is absolutely the best advice. Everyone should have hydrometers and should check the batts as you say. From today we should ask: Do you have a hydrometer? Yes, right, check the readings and record them and if out of whack, then equalise. Have altered my post above to reflect same. On bigger systems, taking reading frequently (even daily!) will quickly help detect problems which you may not otherwise see / detect. ___ 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 Right, the door has now been opened for newbies to get into gravity measuring per cell. Been waiting a long time to bring this to the table. Think we should start a thread on this. Anyone who is good at explaining to start one for education purposes? Quote Link to comment Share on other sites More sharing options...
OomD Posted August 22, 2016 Share Posted August 22, 2016 Just for my interest, why should one not exceed 2 hours (or thereabouts) when charging at > 13%? Purely because of efficiency reasons? Or bad for batteries? Quote Link to comment Share on other sites More sharing options...
SilverNodashi Posted August 22, 2016 Share Posted August 22, 2016 28 minutes ago, The Terrible Triplett said: Right, the door has now been opened for newbies to get into gravity measuring per cell. Been waiting a long time to bring this to the table. Think we should start a thread on this. Anyone who is good at explaining to start one for education purposes? My neighbor duly measures his two battery banks (connected to 2x 5KW Microcare inverters) every morning, and every evening. Been serving him very well from day one and he occasionally drains it to 0, when it's cloudy / rainy, without any side effects. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 44 minutes ago, OomD said: Just for my interest, why should one not exceed 2 hours (or thereabouts) when charging at > 13%? Purely because of efficiency reasons? Or bad for batteries? We spoke of this before when you said you use a lot of water. If your charge current is too high the batts get hotter during charging. A symptom of this is excessive water usage. Here is a good library of information on all things battery related: http://batteryuniversity.com/learn/ Quote Link to comment Share on other sites More sharing options...
___ Posted August 22, 2016 Share Posted August 22, 2016 45 minutes ago, The Terrible Triplett said: If your charge current is too high the batts get hotter during charging. A symptom of this is excessive water usage. Oh it is really simple. Back to basics. A battery changes chemical energy into electrical energy and vice versa. Chemical reactions need TIME to happen. There. That is it. That's the basics that belie all charge and discharge rates. When you charge or discharge too fast, you're not giving the chemical reactions enough time to happen, and the result is a drop in efficiency. On charging, the surplus current just causes gassing, so you're losing water (gassing is especially bad on AGMs), making heat, cooking active material from the lead plates, etc. On discharge, you drop the terminal voltage too much, causing the work to be done at a lower voltage, inverters to compensate with more current, leading to more amps being used and deeper DoD in the end... not to mention Peukert. All battery related rates comes back to this: The chemical reaction needs time to happen. Edit: Of course, if you really overdo it, you can make so much gas that the vents can't keep up and you can literally blow the battery up like a balloon (I've seen a 7Ah sealed alarm battery that's had that done to it). You can also make them so hot that they go into thermal runaway and... I've never actually seen that, but apparently it ain't pretty. Quote Link to comment Share on other sites More sharing options...
OomD Posted August 22, 2016 Share Posted August 22, 2016 49 minutes ago, The Terrible Triplett said: We spoke of this before when you said you use a lot of water. If your charge current is too high the batts get hotter during charging. A symptom of this is excessive water usage. Here is a good library of information on all things battery related: http://batteryuniversity.com/learn/ Mmmm, you may be confusing me with someone else. Either that, or my Alzheimers is acting up. I don't use water, I have AGM batteries... But thanks for the info nonetheless. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 Just now, OomD said: Mmmm, you may be confusing me with someone else. Either that, or my Alzheimers is acting up. I don't use water, I have AGM batteries... Apologies. Must be my Alzheimers then, getting people konfussed. Similar question was discussed a few weeks back. Quote Link to comment Share on other sites More sharing options...
PaulF007 Posted August 22, 2016 Share Posted August 22, 2016 On 7/22/2016 at 11:57 AM, The Terrible Triplett said: Axpert can pull more amps from the panels without affecting the max battery charge setting I am told. Very cool feature. @The Terrible Triplett I have now looked through every thing on the forum is this the first time you have deemed the Axpert Cool ??? Even some Blue bulls started to screeem Lion this year so maybe it is time for Blue to turn .... ___ and Chris Hobson 2 Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 Just now, PaulF007 said: @The Terrible Triplett I have now looked through every thing on the forum is this the first time you have deemed the Axpert Cool ??? Even some Blue bulls started to screeem Lion this year so maybe it is time for Blue to turn .... Some people think I just hate Volctronic's just because. But if they read carefully, as you have, they may find a few more gems like that one here and there. Quote Link to comment Share on other sites More sharing options...
PaulF007 Posted August 22, 2016 Share Posted August 22, 2016 As long as they keep on coming my friend , by now you should be aware that your approval is held in high regard! Chris Hobson 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted August 22, 2016 Share Posted August 22, 2016 1 minute ago, PaulF007 said: As long as they keep on coming my friend , by now you should be aware that your approval is held in high regard! Really? I don't think so. Have decided, based on this forum, when I spoke to you the first time, that Axperts are THE best inverters to learn from, especially if you have a BMV and software in place and are technically minded. Spend the monies on panels, their mounting and a BMV monitor, then batteries and lastly inverter, for that is where the Axpert comes in quite nicely, a small bank and large array for daytime use. Quote Link to comment Share on other sites More sharing options...
___ Posted August 22, 2016 Share Posted August 22, 2016 4 minutes ago, The Terrible Triplett said: Axperts are THE best inverters to learn from As your fellow blue fan, allow me to interject... :-) My position is similar. I believe the Axpert is exceptionally good value for money BUT... I say that only because they cost so *#$!! little money! Literally R2.50/watt, including an MPPT and a transfer switch! And it is precisely this that makes me suspicious... it is too good to be true, and you know what conventional wisdom has to say about that. I have however never worked with them, seen them om the inside, I literally have zero experience with them. Hence I cannot, or rather should not judge. Putting aside then the slight mistrust: It is very accessible, and brings together cool features (such as that MPPT/self-consumption interlink), and though they were not the first company with that idea, they were the first to make it really affordable. One should give credit where credit is due. But I still can't bring myself to like them. And I also cannot apply the "learner equipment" argument to it either, but perhaps that is because I'm a little less prone to blowing stuff up. I suppose if I was a smoke releaser, I'd also prefer to do it to a 7k piece of equipment rather than a 20k piece of equipment. Quote Link to comment Share on other sites More sharing options...
PaulF007 Posted August 22, 2016 Share Posted August 22, 2016 3 minutes ago, plonkster said: And I also cannot apply the "learner equipment" argument to it either, but perhaps that is because I'm a little less prone to blowing stuff up. I suppose if I was a smoke releaser, I'd also prefer to do it to a 7k piece of equipment rather than a 20k piece of equipment. The problem with starting out new is that you dont have a clue as to what to expect , for me the Axpert was a method of risk management (Keep in mind that I bought mine used). If you go and spend 20 - 30k on a inverter system only to realize that you went into the wrong direction was a bit of a problem for me , my outlook on solar energy has shifted so many time's in the last few weeks that I have stopped counting. The way I looked at it was Panels will be panels and you will be able to use them with any system even if you have to cut the wire to change the array on them. So dont screw around on them . IF you can get a cheap inverter and learn from that it should put you in a position to buy a "proper" unit in future , and if the inverter servers you for a reasonable time even better. If you chat to a guy like @edmundp you come to realize the short comings of these units and that you need to adapt to compensate , most of us buy a BMV 700 to monitor the Batts because you cant trust the Axpert's readings some has even come to realise that the voltage readings on the charge controller isn't up to speck either and you need to measure that as well to make sure the out put is that the Software say else compensate. The problem arises if you buy a Axepert with your last cash with the hope that it will last you 10 Years and if it doesn't you are screwed then you will run into problem quite simply because your approach is wrong. For you guys that has been around the block a couple of time and have sorted out your base loads , peak loads and the misses , imo will be silly to look at the Axpert but for a starter... Last bit of my personal experience I live in a small community and "in the land of the Blind one Eye is king" ... so all of a sudden I get call's from people that want to go Solar and my advice is Head to PF and start reading A LOT Cut your base load on Eskom until there is no more to cut and then you start over again and cut again Once you have done this get a solar geaser If by then you are spending R 200 on electricity dont go solar else get a new low consumption wife , So all and all live like you are on solar and then go and buy all the shiny things - else get a cheap Axpert and accept that you will replace in 5 years time .. Jy kan nie a Toyota gaan loop koop met n Tatta se geld nie but the Tatta will also get you there .... KLEVA and superdiy 2 Quote Link to comment Share on other sites More sharing options...
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