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Forum Index : Solar : High Capacity 12vdc system
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| Boppa Guru  Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I know (and agree with) all the arguments for going for higher voltages on the dc side of things, however I have an existing 12vdc 8kw blackjack inverter, and have just been given (for free) another 5kw 12vdc inverter I also have access (for next to no cost) several tens of meters of 1/2" x 4" copper bars plus a lot of existing 12vdc gear from the truck- 70l fridge, another 40l fridge/freezer, literally dozens of 12v/24v led lights etc etc So I am beginning to think I might do something stupid- and stay with a 12vdc solar system Looking at Winston batts (1000ah) 4 in series to provide the 12vdc bank- maybe another 4 in parallel with them to make a 2000ahr bank if required for the workshop- I dont know whether that will be ness at this stage tho The question I have is- panels- I was looking at 2nd hand 190-250w ex grid panels- but I'd like to string multiple groups of mttp controllers in parallel to get up around the 10-15kw region but obviously charging the 12v bank- Is it possible to use the mttp regs in such a fashion (ie several strings of series/ parallel panels all with their own reg, all feeding the one battery bank) ???? The 12vdc system would be quite short in distance- maybe 10m long all feeding into a 3000a multiple busbar system (1"x4") with the batts and inverter in its own shed right at the panels, with a 240v supply to the house and shed I cant see any real issues with using such a system (I know it isnt optimal, but with getting so much 12v stuff for free or next to it, my only real costs will be panels (60-75 bucks per panel 2ndhand) and the batts) thoughts? Insane??? doable??? (I've crunched the numbers and it appears doable, unless I've missed something) |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I noticed the word Winston. So the batteries will be LiFePO4? Will the MPPT controllers properly charge the proposed batteries and protect them? |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Dont see why not, most of the better ones have programmable voltages anyway The inverter was my biggest concern as it doesnt have a programble cutoff voltage, its set and trips in at 11.2- which is right at the lower end for discharging them, id be happier with changing that if I could up to 11.8 or even higher The 1000ahr ones look a good match to my inverter both in max draw rate is only half of the batts max delivery rate (not that id be drawing anywhere near that most of the time, but it would be nice to have the capacity available and having a lot of reserve power available (as I'd eventually be running a hobby cnc workshop off it as well), so no point having undersized batts- been there and done that years ago, imho you can never have too much batts or solar The problem is that if I put the house right at the front of the block, its 25g to get power on, putting it where I want to is likely to double that- that leaves me a lot of wriggle room for building one hell of a system... I like the winstons, we put a set in my stepfathers ute and they have been great so far, no issues apart from some idiot wiring up the balancer wrong and letting the smoke out.... whistles innocently I actually took photos of the entire process, must put them up one day, he's a picky bloke when it comes to his kit... They seem to be great at running the car fridge (used for weekly shopping as well as when camping etc) led lighting, ciggy lighter sockets (there is 9 in the entire car- from the factory!!!- including one in the ute tub.... |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
OK, I see you are familiar with LiFePO4. Likewise, that was one reason I was asking about protection. My SolarBMS has programmable LVD and HVD, but I also have my own LVD and HVD protection as a "back-up". Wasn't keen to lose multi Ks worth of batteries. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It would be quite easy to make an external under voltage shutdown with a Gigavac bistable relay. An undervoltage threshold detector would pulse the relay off, and it would remain off, even after the battery voltage bounces back up after the discharging load is removed. For lower current applications, a dc rated circuit breaker fitted with a shunt trip coil might be a lower cost option. I use a good quality digital panel meter to monitor battery voltage that has two programmable alarms that I use to trip the battery circuit breaker for under voltage or over voltage as "last resort" battery protection. Cheers, Tony. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
If you did not have the programmable device it would be quite easy to use an Arduino to monitor the voltage you also would be best to have a time delay to prevent tripping due to brief high current draw. A more simple circuit using a 555 timer would do the job also. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Many ways to do this. A resistor and electrolytic should be all that is needed to prevent false tripping from noise. A TL431 would probably make the simplest voltage detector. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I thought Id seen every 555 circuit configuration under the sun, but there you go, yet ANOTHER use for a 555!!! (is there anything a 555 cant do?) I liked the latching Gigavac bistable relay idea, but its current is a little on the low side, handy hint for those that want a high capacity low voltage (12vdc 40A/15A) you can use a vw t2 kombi headlight dipping relay (HELLA 3057), alternate switches with a single pulse of approx 120ma for <500mS, rated at 40A on the high beam circuit, 15A on low beam circuit, about 10-15 bucks from hella retailers Not sure on the inverter tho (cutoffs not obviously adjustable altho I havent had a good gander inside) as its a pretty heavy draw ~700A so relay switching it directly is unlikely- I think from memory it has remote switching was a option although not obviously apparent how on mine (no socket/connector externally- maybe inside?) or switch the actual front panel switch with a relay... I cant remember the brand (the ute is in NSW) but Trev supplied a monitor system to go with the batts, took up to 8 cells, has relay output fully programmable for undervolts, overvolts, single cell difference, all sorts of fun things (mounted above the 12v socket for fridge)  |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
There is this 400 amp version that should work for a 5Kw 12v inverter. 12v coil, latching operation: http://www.gigavac.com/sites/default/files/catalog/spec_sheet/gvL144.pdf Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Still a little low for switching the inverter directly if its at full steam, although admittedly that isnt likely to happen often- the front panel switch is just one of those little 5a red rockers, so I think its most likely that if it doesnt already have a connection point for switching it, I'll just put a changeover relay onto that to kill the inverter on low voltage I actually dont see a lowvolts being likely to happen very often with this system, but I'd prefer to have provision for it just in case, I found a nice little 15kw diesel genpack for $6g that looks perfect for a standby as well |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I was thinking of running all the lighting etc off 12vdc as well, run a pair of busbars to the house from the battery shed and up into the roof (4" x 1/2") then just elv wiring as required (4mm) to individual lights, outlets etc, the busbars would be extremely oversized for the currents involved but would minimise any voltage drop, and as I said its basically free (all I got to do it drive and pick it up) Got tons of 12/24v led lighting (ex truck mostly those big 6x4" rectangular led lights you see on semis, plus about a dozen 12/24v led spotlights (4" and 6" circular and led lightbars) I was looking at using as yard lights The busbars are actually lightning grounding strips that were used on anfo plants to connect their lightning rods to ground on the big sheds, left over after the mining boom in qld stopped and were picked up by a mate of mine for free after the supplier shut down, they were just left lying in the yard of the old factory they were working out of and he had to clean all their junk out of it (they literally just closed thje doors and walked away leaving everything behind) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
[quote]Still a little low for switching the inverter directly [/quote] What are you running there Boppa !! Those relays will make or break a couple of thousand amps plus... easily and reliably. [quote]I actually dont see a lowvolts being likely to happen very often[/quote] With Lithium batteries just one event will definitely cause irreversible damage. Just not worth the risk. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I found a `sneaky' way of converting the six billion ciggy lighter sockets in the ute to run off the back batterys easily, without having to modify the cars wiring in any way (the car radio also now runs off the back batterys as well as the interior cabin lights) I bought a few of these inline fuse addon from jaycar, a couple of bucks each... I deliberately `blew' the actual fuse, then connect the `addon' wire to the rear batterys, remove the appropriate fuses from the cars fusebox and add these (obvious you have to check to see which side is the supply and which is the load, fit with the wire on the load side)- connect wires to feed from back batterys (add new fuses at back battery for safety!!!) Bingo instant circuits running off back battery, and can be pulled from car within seconds, just refit original fuses to reconnect to original battery handy little trick and easy to do |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Its a blackjack style 8kw cont, 12kw peak inverter, I have seen my ammeter peaking at 700A plus using a stick welder on it camping (how accurate it is I wouldnt like to say tho) Oh ok, I saw the link was rated at 400a, and was thinking it was still under my inverters current rating True, I want belts and braces on this system, there is the monitors lowvolt cutout, the inverters one (that I dont like as it is imho too low for safety on the batts, but I want it to also trigger on individual cells dropping too low as well as pack voltage, so if one cell drops early for whatever reason it wont kill my batts... I like those units btw- just need a pulse to activate (I looked at a heavy duty solenoid at first but ones rated at the current levels I am talking about literally drew amps to hold in- unacceptable lol) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It does not need to be a pulse to activate. You can continuously drive either coil without any problems. Its just that a pulse is sometimes very convenient, both for activation, and for the reset button. These bistable relays operate like a see-saw. Its like mechanical flip flop. There is a fairly strong bias magnet that holds the contact either open or closed. Either coil makes the see-saw tilt in the opposite direction. You could easily parallel up a couple of these relays, but I truly doubt that would be necessary. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Very similar to the vw headlight dip relays in operation (I found them very useful for anything in a car like alarm triggers or lv cutoffs where you dont want a continuous current draw on the battery, just a quick pulse and they trigger from one output to the other and stay that way until the next pulse where they switch back again) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
[quote]Very similar to the vw headlight dip relays in operation[/quote] I have not seen those, very interesting. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I used to work at a vw restorers so know a bit about em lol They used those relays so that when you briefly grounded the dip switch (on the steering column) they flicked from high beam to low (or vice versa) From memory had + on the 30 & 86, 85 went to the spring loaded dipper (momentary)switch, 87 went to 2 fuses then to each high beam, 87a went to 2 fuses then to the two low beams (hence the 15A/40A ratings) For many years I used one as my alarm system, it had a 12v flashing led on one output, that also led to a very very loud siren mounted inside the cabin of the car with a self latching relay to hold it on once triggered by the door light switches (normal relay wired so once power was applied to the coil, it pulled in the contacts, that then fed power to the coil and siren- had to find the hidden switch to turn it off!) The vw latching relay was triggered by a reed switch mounted under the rubber of the drivers window and I had a small magnet on the key ring- tap it on the rubber while looking in through the glass at the flash led on the dashboard- flashing was armed dont open door!!!, no flashing was safe to enter... One (semilegal- didnt have a timer) alarm system for about $20, when store bought ones at the time were $300 plus (this was back in the late eighties) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Latching relays make excellent undervoltage disconnects, because they can keep things switched off without needing to draw any further continuous power to do so. Its not so bad with an overvoltage disconnect, because there is power there to spare. Once the battery is isolated, the terminal voltage rises back up under no load, and you don't want the system to start up again until its properly reset. When it hits that low dip, you want it OFF. If it then rises back up it should stay locked off. Definitely agree with the belt and braces approach. There should be at least two completely independently operating systems for both undervoltage and overvoltage battery disconnect. Cheers, Tony. |
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