how do I know its a 24 volt panel.

[Kappy]

Sounds almost like sack the Bus and ride my Harley. or buy some new AGMs and a BMV700 and see what happens.

[T1 Terry]

Only you can make that call Kappy, best to be armed with as much knowledge as you can get to make the decision on which way suits you best. It is better to make a well informed investment that you will be happy with and can live with than taking the easiest path and regretting it in the near future. Do it right and you will only need to do it once, but which way is the right way ?

[native pepper]

Sounds almost like sack the Bus and ride my Harley. or buy some new AGMs and a BMV700 and see what happens.

Kappy, it is not as complicated and dangerous as some make out, in fact setting up a bus system is very simple if you use the right gear. There are many using mppt controllers with lifepo4, I know of some that are 8 years down the track with them and myself, 6 years on my portable pack, 5years on my house and 3-4 on the bus. I also know those who have done close to 10 years testing mppt against pwm and they continue using mppt for off grid.

When I changed from pwm to mppt controllers on the bus, it had 260w solar, 360amp gel batteries and struggled to give us enough power to run lights an the TV for a couple of hours a day. Off course the small system made it harder and if we were in shade or it was cloudy, you could kiss decent charging good bye for the day. When i got my first mppt, on the advice of my late mate, the difference on such a small system was amazing. When I added 200w more solar, we thought we were in heaven. Then my mate gave me enough lifepo4 cells to make up a 120amp x 12v pack to play with, he told me later he wanted an electronics dummy to use them and see how they went. I had a bit of trouble setting up the BMS and active balancers, and after a couple of years of stuffing round with them and constantly having to watch them charge and bleed a cell or two as the balancers didn't work fast enough, he gave me a prototype of his mppt bulk charger and we ditched the bms and used relays to switch off power to the pack.

Then about a year or so before he passed away, he gave me a cell equaliser he had made. This consisted of a circuit board with wires running from it to each cell line and I connected that to 120amp pack I'd made up. Now I have a system which is simple to put together, controls the cells wonderfully and the mppt controllers handle the 4.5kw of panels on my glass house roof, which faces north. That's why I'm about to install inverter A/C in the bus and house, which arrived today, after they sent me the wrong ones. I'm also putting 1000w of solar on the bus and have already tested the system running 2 x40amp bulk mppt controllers, which runs beautifully. I've proven this with my house system, which has 7 x 60amp mppt controllers, all connected to the one lifepo4 pack, which have a cell equaliser connected to each cell line and my simple cheap ebay cell monitors keep me informed as to the state of the cell line and current capacity. I have an cheap ebay input amp meter which shows how much is going in and out,the system just works.

Many off grid installers have said my house system is to bulky and I should have just one or two big controllers, but my mate used to say, if you have big capacity cells, big capacity controllers and something goes wring, you lose your system. But with his approach, if something goes wrong with one part of the system you have the rest of the setup to keep providing power.

If you keep your system simple with proper controls, it's a simple easy process. And the insurance is in using small cell sizes, eg 40-60amps, a bulk charger and cell balancers, in my opinion. However most RV users I've run across, have big cell sizes, which come in plastic, the cells I have come in metal cases, which I'm told are far superior to plastic for many reasons. As I no longer have someone to refer to and am clueless in that regard, I can't be sure of that, but from what Ive seen over the years, it's pretty true.

If you decide to go ahead and want go get a bulk solar charge controller, our group will be getting some more in the near future I believe and i think some balancers. The balancers you can get on ebay, the price we get them for is not much cheaper, but the controllers are unique and we get them way cheaper than the programmable lead acid controllers most use.

I love the simplicity and security my system gives me, and would be happy to ask the group to include some others in their next purchase. They are not into it for profit, but to save money and get good equipment. Most involved like me are building systems up, so we get what we can afford and between the group of us, that brings the price down and then we save up and get some more. I hope to have between 10-20kw on my house and workshop within the next year or so and will be getting another 6 x 60amp controllers in the next buy, nothing like having spares. I get my panels from ebay, at less than $250 for a 250w x 24v panel delivered, I get a couple each 2 months or so and to get then cheaper, we'd have to buy a container load.

[SteveW]

So what are you saying NP? On more than one occasion you have said "I am not an expert " or similar words, but once again when Terry has given good, and might I add, free advice you have stepped in to confuse the issue!

Sent from my SM-N910G using Tapatalk

[SteveW]

Just had a nice lunch with my good friends - I am very wise after lunch.

Sent from my SM-N910G using Tapatalk

[T1 Terry]

8 yrs experience using MPPT with LiFeP04, really? All that have carried out side by side testing using panels within the voltage range that suit the battery have only taken a few weeks to come up with the realisation, some did go through a lot of controllers because they were so sold on the logic regarding MPPT being superior, but honest tests reading the output always comes up with the same reality check, MPPT is not all it is hyped up to be and not in the ball park compared to a well set up PWM solid state relay control system. It has been tested on 12v, 24v and 48v, the difference simply reflects the same improvement of the PWM + SSR compared to MPPT.
Once the system size starts requiring multiple controllers or series/parallel strings to keep the series string voltage within the controller limits the differences start to run away rather than just a step ahead.
Unless you have a mis-match between panel voltage and battery voltage, MPPT is a step in the wrong direction and if you take the time to put it to the test you will come up with the same result.

T1 Terry

[Kappy]

Only you can make that call Kappy, best to be armed with as much knowledge as you can get to make the decision on which way suits you best. It is better to make a well informed investment that you will be happy with and can live with than taking the easiest path and regretting it in the near future. Do it right and you will only need to do it once, but which way is the right way ?

The bus was set with 600 watt of solar and 200 ah of AGM, that look as though they had passed the Use by date so I don't know if they are actually the problem.

The bus was set up to run on 24 volt not by me but the guy I brought it off, the fridge and lights,pumps run ok off 24 volt the inverter was a modified Sine wave that wouldn't run an A/C and did I mention the AGM's are toast. So I thought I would replace with LifePo.

Advice seems to back that.

Then I thought I would change to 12 Volt and lithium, then I discover I need heavier wire, so do I have to rpelace all the wiring throughout the bus or is that around the panels/batteries haven't discovered where.

Thought I would stay with 24 seemed to work sorta before AGM's died and add more panels for power generation.

So am I confused you betcha, a lot of the advise I have sifted through seems at times contradictory, for a lay person like me and when I think I got my head around it someone throws something else in the mix.

[native pepper]

Terry, I'm only saying what I have experienced and seen, never had a problem with my controllers connected to the packs and maybe PWM is better, but never used them since I got mppt and still think I have a good system. To me as many peoples experiences is important, unless some one is trying to control the market or something like that. Having talked to and listened to many supposed electrical experts, some with many degrees and experience, have found just about all disagree with each other.

On a yank solar forum I had a look at some time ago, there was an argument between some supposed experts claiming they had lots of qualifications and experience and none of them could agree on anything to do with solar, lifepo4 and chargers, they even differed on lead acid and claimed lifepo4 were useless with short life spans. The banned me when i said had a pack over 7 years old at the time and they were fine with the usage parameters I used and we had dedicated lifepo4 controllers, which they claimed didn't exist and lead acid controllers were fine for lifepo4. Still get told our charge controllers can't work, even had an off grid installation expert tell me that, whilst watching my house system in operation.

Have found that with every forum I've checked out regarding lifepo4 and solar since my mate left, they argue using lots of technical jargon and get nowhere, other than to maintain they are right and everyone else is wrong. Sometimes I think the arguments of experts are restricted because they are so locked into their ideals, that's all they can see. Whilst someone like me who has no real knowledge and understanding, ends up working it out for themselves as to the best approach and changing if they see the need.

I've not seen any runaway voltages as you say, nor any loss from the mppt controllers, or them competing with each other. They all shut down at the same time and with the equalisers, it has made it so much easier than using bms, relays and balancers. Pus I don't understand unexplained logic and the controllers I use are designed for using along side others, they are not your run of the mill off the shelf brand name or el cheapo chinese controllers and may make a difference.

If as you say mppt don't work in parallel, why are they all advertised and sold as being capable of parallel use. I can also understand there may be problems when using mppt charge controllers with other parameters other than bulk, as they may have trouble deciding when to switch from bulk to float to equalisation and temp controls. But using a single stage charger, wouldn't that eliminate any confusion, just off and on, and no slowdown or restriction to input. Having not used lead acid pwm controller on my house since getting lifepo4, can't comment on the difference in performance and only had a smaller array, compared to today.

Could you provide a link which supports your contention, so I can understand the theory behind it, every site Ive gone to that discusses the use of multiple controllers in series, recommends the same style of set up we use. each controller has it's own array, in my case 750w for 50amp and 500w for 40amp and they all connect separately to the pack. If the entire system is say 1000amp lifepo4, then they would be in two banks of 500amps connected to however many controllers you have for each pack. I've realised how much I relied upon my mate for decades of electrical knowledge, now have to do it all my self. So my questions are to learn, not to offend or start an argument and if you don't question and reveal your understanding, there is no learning, or progression in knowledge.

[T1 Terry]

Only you can make that call Kappy, best to be armed with as much knowledge as you can get to make the decision on which way suits you best. It is better to make a well informed investment that you will be happy with and can live with than taking the easiest path and regretting it in the near future. Do it right and you will only need to do it once, but which way is the right way ?

The bus was set with 600 watt of solar and 200 ah of AGM, that look as though they had passed the Use by date so I don't know if they are actually the problem.

The bus was set up to run on 24 volt not by me but the guy I brought it off, the fridge and lights,pumps run ok off 24 volt the inverter was a modified Sine wave that wouldn't run an A/C and did I mention the AGM's are toast. So I thought I would replace with LifePo.

Advice seems to back that.

Then I thought I would change to 12 Volt and lithium, then I discover I need heavier wire, so do I have to rpelace all the wiring throughout the bus or is that around the panels/batteries haven't discovered where.

Thought I would stay with 24 seemed to work sorta before AGM's died and add more panels for power generation.

So am I confused you betcha, a lot of the advise I have sifted through seems at times contradictory, for a lay person like me and when I think I got my head around it someone throws something else in the mix.

I'm guessing you aren't the only one Kappy There are so many experts ready to share their beliefs yet have very little technical expertise and virtually no side by side testing to verify their beliefs, you are just expected to have faith that they know best.
I don't claim to know it all, still learning after 6 yrs hands on testing, but with a few hundred systems out there now all making their owners very happy they went with my advice I fell I must be getting close to getting it right

On another thread about increasing the output of a 20 amp PWM controller all the experts said it wouldn't work, then said it wasn't efficient, now they say someone else came up with the idea first, not that it doesn't work because that can't be claimed any more ..... so much for experts eh
The solar cabling will need to be up to carrying the current involved no matter if it's 12v or 24v so it will probably need to be upgraded, unlikely any other wiring will need to be upgraded besides the high draw stuff like inverters and fridges if they run 12v, but again that idea that wouldn't work of using a 240vac inverter fridge seems to be the way to go with many very happy people doing the impossible, so that just leaves the inverter and you already knew you would need to upgrade that cabling if you wanted to run the air con

T1 Terry

[T1 Terry]

Hi NP, I'm guessing you are having some limited success because you run a hybrid of lead acid and lithium, not straight lithium and only one battery. If it works for you then that is all you can ask for, but it does not mean it will work for others the same way as it works for you unless they have the same set up. Most people don't want to throw away what they already have, the want their existing equipment to work with lithium batteries and that is where we come in. If the system already has MPPT controllers then we can work with them if that is what they want, we simply advise that there is a better way and have the hands on look with your own eyes proof. Read all you like, actually seeing the results in person quickly sorts the wheat from the chaff.

T1 Terry