In alt.engineering.electrical
[email protected] wrote:
| On Aug 14, 2:52 am,
[email protected] wrote:
|> In alt.engineering.electrical
[email protected] wrote:
|>
|> | Batteries are the very heart of your system. That should tell you
|> | something about the choice of battery/ cell used. You sound like a guy
|> | looking for an excuse to use golf cart batteries.
|>
|> You sound like a guy wanting to tell everyone to do things exactly the
|> same way you do things, without being willing to tell them why, whether
|> you actually know why or not.
|
| I have told you why, parallel strings do not charge/discharge in a
| uniform manner. That is the truth.
I'm not doubting the truth of this. I'm wanting to understand the means
by which this happens, and the degree to which it happens. I want to
understand this enough to know how well it may be mitigated. For example
the non-uniform charging may be dealt with by smaller chargers isolated
on each string (not one big charger trying charge the strings in parallel).
|> | Best choice is a single series string of the correct capacity. Failing
|> | that being possible the second best option is no more than 2 parallel
|> | strings to make up the capacity.
|>
|> Why?
|
| I have told you why, parallel strings do not charge/discharge in a
| uniform manner. That is the truth.
I'm not doubting the truth of this. I'm wanting to understand the means
by which this happens, and the degree to which it happens. I want to
understand this enough to know how well it may be mitigated. For example
the non-uniform charging may be dealt with by smaller chargers isolated
on each string (not one big charger trying charge the strings in parallel).
|> Specifically I want to know why for the "no more than 2" part. But I
|> also want to know how to balance the decision between first best and
|> second best against other factors that may push for that second best.
|> Merely ordering the option into 1st, 2nd, 3rd, etc., is not it.
|
| Two strings is manageable without to much pissing about. The decision
| is to buy a single string of the correct Ah capacity.
| If this is not possible then use two parallel strings. Money before
| good design is false economy.
I would not say it is not possible. But there may be (when it comes time
to do this) reasons to prefer the smaller batteries. Reasons can include
the desire for one man handling (can depend on available space). Or it
could be the desire to start small and migrate to larger.
I want to explore means to manage the load balancing before deciding.
Maybe it will be the case that those methods are not worthwhile. I
cannot say today. Today is the learning time. The decision is later.
The conditions will be known then.
|> | Your choice, you spend the money, you wear the consequences. Let's say
|> | you are willing to spend half a million to build your house, you're
|> | going to quibble over 50k to power it.
|>
|> If you have nothing more to add, then what you have said so far will not
|> play much, if any, role in my evaluation of the designs to use. This is
|> because you aren't providing information I consider useful. Again, I am
|> interested in the technical information to go into a design decision that
|> balances multiple needs, not the "what I did" or "what I would do" (unless
|> I get a sufficiently significant number of those responses from verified
|> engineers).
|
| Not true. You want someone to give you a good reason to choose the
| lowest price option over good design.
No. I want to know all the reasons for all the choices.
| No matter what you decide, be it a single string or six parallel
| strings, if one cell dies and the batteries are older than a yera or
| two then you will be replacing th whole bank. That the way it works.
What happens if you have ONE string of several very large cells/batteries
and one dies? Are you saying you don't have to replace the whole bank in
this case?
|> I expect to pay more than the cost of being on-grid. But this is NOT an
|> infinite finance to work in.
|
| You have a grid connection, you will find that PV can not replicate
| that level of energy for what you feel is a reasonable cost. What have
| you done to reduce your energy needs.
That is a work in progress. Much of it will be done when I start going
with some battery power. More will be done later. This is not a one big
step all the way project.
|> I want to do it with one person. Maybe that means a fork lift machine and
|> the space to move the fork lift around. Or maybe it means a block and
|> tackle assembly that can slide on an overhead rail. Or maybe it means all
|> the cells/batteries placed on individual roller carts with locking wheels.
|> Or maybe it means having smaller batteries and doing the lifting more often.
|> All these options are best balanced out knowing all information (not just
|> the cost, but also the technical implications, the latter of which I was
|> hoping I could get pointers to from someone here).
|
| You have been given a great deal of information in this thread.
Quite a lot of it is unsupported "what to do" advice.
|> They can do things like ensuring that one bank does not cross change another.
|> They can allow separate chargers for each bank.
|
| A diode is not a rectifier.
Rectifiers are made of diodes (or other things).
|> |> I'm exploring all options. I'm not interested in specific advice on what
|> |> I should do (at least not without well explained why) ... I'm interested in
|> |> the information to make the best decision in the circumstances that will be
|> |> present at the time the decision is to be made.
|> |
|> | You still sound like a guy looking for an excuse to use golf cart
|> | batteries.
|>
|> I am someone looking for the technical information that would be a valid basis
|> for deciding what circumstances that golf cart batteries can be used in, and
|> what circumstances they cannot be used in, where "circumstances" involves a lot
|> of things that I don't even know, yet.
|
| You can use golf cart batteries, they can be wired in series, parallel
| and series/parallel in as many strings as you feel are required. Most
| people only ever do this once. Their second battery bank is usually a
| single string of cells with the correct Ah rating.
And maybe I will migrate to that. One possible path is that I would start with
a small bank and migrate to a larger bank. I may parallel things in the interim.
I will also be looking at possible circuits to manage the load balancing between
parallel strings. Maybe that won't be practical. I'm sure you'll say it won't
but I want to know why, if that's the case.
| Parallel strings do not charge/discharge evenly. Two strings and you
| must monitor the state of charge and equalize the strings more often.
| Basically twice the work of a single string. Three parallel strings
| and you might expect to do four times the maintenance. In the end you
| will have repetitive cell failure. Because of the cost you will
| replace cells/batteries rather than replacing the whole bank, then you
| will remove a string to use the cells/batteries to replace dead cells/
| batteries in the remaining strings.
If it is the case that cost is why I would replace one cell/battery at a
time, then cost would clearly prohibit the monster cells.
| I know, you would never do that.
I believe I can make the right decision ... the one that is right for my
situation, once I know all the issues, how they behave, their workarounds,
methods of managing them, etc.
|> Days of autonomy will gradually shift to being whatever number of days God
|> decides not to offer me the opportunity to charge up (e.g. no wind, no sun).
|
| No. you have to decide when designing your system. This is one of the
| factors that sizes the battery bank.
| God doesn't give a rats ass whether you sit in the dark or not,
|> I can't say some particular exact number of days I want to be sure the system
|> will continue to operate in. If I say some number, I have to face the issue
|> of what to do when it happens to turn out longer than that. I expect to start
|> with a low number and build up to a higher number.
|
| "DAYS of AUTONOMY" is not a sliding scale. It is what your batteries
| will provide at the load designed for. What are you going to do, add
| and subtract batteries as required?
Apparently we have a different understand of this term. I don't know
what yours is, then. So it's pointless to proceed on this.
|> |> |> And maybe some big rectifiers to isolate the strings from cross-charging might
|> |> |> be called for. It would then seem to me the only way to keep the strings
|> |> |> charged with the rectifiers in place is to separately charge each string.
|> |> |> But that might be an economic benefit from smaller chargers.
|> |> |
|> |> | Been there, done that, didn't work and the tee shirt dissolved in the
|> |> | wash.
|> |>
|> |> Do you know why it didn't work? Or are you just assuming that because it had
|> |> rectifiers, that must be why?
|> |
|> | Sorry, no rectifiers. Did try diodes. Oh, it worked alright. It was
|> | just not worth the effort. The strings always ended up at different
|> | voltages and needing charging to bring them back into line. Then there
|> | was the game of musical cells trying to get a balance in each string.
|>
|> Did each string have its own charger and charge controller?
|
| Hang on. You want the cheapest option. Now you want to build multiple
| systems.
Your understanding of "cheapest option" is likely not the same as mine.
|> | But if you have the time on your hands, go for it.
|>
|> I don't know whether I will or won't. I'm looking for the specific technical
|> info to learn that allows me to figure it out. I do not know if you know what
|> it is I want to know, or not. But I do know you are not saying it, or pointing
|> to it, for whatever reason that might be.
|
| Oh, I know what it is you want to know alright. But to understand you
| need to listen.
| You want some one to tell you what you want to hear.
You want some one to do what you tell them to.
I can see I'm not going to get anything useful from you.
====
