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48V LTO Off Grid system
#31
One more question.. which are indeed getting dumber.

There are not so many BMS out there yet that specifically state they are for LTO. But there are a number which are programmable (charge voltage , discharge voltage etc). But their advertised series setting don't naturally fit LTO eg 5S for 12 V.

As a general rule can you connect, say 5S arrangement to an 8S BMS (leaving 3 connectors unused) ? and it will work away happily?
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#32
actually, no. for 2 reasons
1) the overall voltage is not what it expects because it's missing 2 connections
2) over time the cells will become unbalanced because 2 of them are not part of the balancing string
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#33
(11-06-2018, 01:32 AM)mblowes Wrote: One more question.. which are indeed getting dumber.

There are not so many BMS out there yet that specifically state they are for LTO.  But there are a number which are programmable (charge voltage , discharge voltage etc).  But their advertised series setting don't naturally fit LTO eg 5S for 12 V.  

As a general rule can you connect, say 5S arrangement to an 8S BMS  (leaving 3 connectors unused) ? and it will work away happily?

I have been testing the 40ah cells for over a year , they can take a lot of abuse.  BMS is a waste of money,

1) they waste energy by a hot resistor , usually a only small amount , 40ah battery is too big for them.

2) They can handle zero volts with no damage , most inverters shut off before that happens

3) Charging them above 400ah probably won't happen

4) Over voltage is the only problem , Use a smart lead acid charger , Not  a regular Dumb charger, they go way over 15v

Balancing is not a problem if you match the internal resistance close as possible within .01 ohm , then you don't need one.

This is hard to do because these cells at 20-30 $ are  Grade "B" cells, they have more resistance variance. It would take a few

  more than you want to buy to get a matched set.

I use a active cell balancer ,To solve that issue, It either charges or discharges a cell to make them equal at any voltage, uses

   very little power.

They are compatible with any battery cell , lead acid to lithium 2v to 5v. This fixes the balancing problem and max out the
 
   power from the group of cells.

https://www.aliexpress.com/item/6S-lithi...rithmid=14
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#34
(11-06-2018, 01:32 AM)mblowes Wrote: One more question.. which are indeed getting dumber.

There are not so many BMS out there yet that specifically state they are for LTO.  But there are a number which are programmable (charge voltage , discharge voltage etc).  But their advertised series setting don't naturally fit LTO eg 5S for 12 V.  

As a general rule can you connect, say 5S arrangement to an 8S BMS  (leaving 3 connectors unused) ? and it will work away happily?

I've seen some diagrams showing you can use them like you want - the unused connections join to the +ve terminal. 
You do need to check it can do typical LTO voltages though.
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Running off solar, DIY & electronics fan :-)
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#35
Jim Jr.. I may well end up just balancers too.. it probably depends a bit on the application. in a boat you normally charge from a generator.. and that is rationed pretty well due to the price of diesel. So much of the time it is heavily monitored charging.

In a home solar though its a bit different.. If I'm around to stick a multi meter in etc that is one thing.. but if this thing lasts 30-50 years then some extra thought is required.. but it could still be just a balancer.. and maybe fuses.

What about fuses?.. I really liked that idea. Seems that the probability of an internal short is low, and if just a single cell on its own, not a big deal at all wth LTO.. But I still worry about an internal short in a large parallel pack .. which I assume would then all dump into the short. Very small chance, but really ugly . Multiply by 50 years rather than 3-5 and maybe its not a very small lifetime chance.

(I ordered a modest BMS today for my test setup)
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#36
(11-06-2018, 02:38 PM)mblowes Wrote: Jim Jr.. I may well end up just balancers too..   it probably depends a bit on the application.  in a boat you normally charge from a generator.. and that is rationed pretty well due to the price of diesel.  So much of the time it is heavily monitored charging.

In a home solar though its a bit different..  If I'm around to stick a multi meter in etc that is one thing.. but if this thing lasts 30-50 years then some extra thought is required.. but it could still be just a balancer.. and maybe fuses.

What about fuses?.. I really liked that idea. Seems that the probability of an internal short is low, and if just a single cell on its own, not a big deal at all wth LTO.. But I still worry about an internal short in a large parallel pack .. which I assume would then all dump into the short.  Very small chance, but really ugly .  Multiply by 50 years rather than 3-5 and maybe its not a very small lifetime chance.

(I ordered a modest BMS today for my test setup)

5 cell setup charged to 14.4v with copper connectors , will put out 1750A and 6 cell setup 14.4v will put out 1500A

Fuses are great insurance at those rates, With a dropped wrench or screw driver , Sparks every where (plus soiled underwear )

These cells will charge in @10 minutes (40ah setup) if you have a 250ah plus alternator .

Diesel ( all motors) have a over head consumption of fuel, I made a setup of a 2ltr thermo-king motor at a idle use 1 quart of fuel

   (600 rpm with 2 cylinders with the glow plugs taken out, and fuel cut out to them ) per hour. Then I connected a 3kw load

    to it and it ran for 55 minutes  per quart of fuel, 9% for power, 91% to keep the motor turning.

Charging in 10 minutes you won't need too much fuel

As for solar charging setup can be setup to dump the extra power when they see that the batteries have reached the max volt

  for charging.
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#37
(11-11-2018, 04:09 AM)Jim Jr. Wrote:
(11-06-2018, 02:38 PM)mblowes Wrote: in a boat you normally charge from a generator.. and that is rationed pretty well due to the price of diesel.  So much of the time it is heavily monitored charging.

Diesel ( all motors) have a over head consumption of fuel, I made a setup of a 2ltr thermo-king motor at a idle use 1 quart of fuel

   (600 rpm with 2 cylinders with the glow plugs taken out, and fuel cut out to them ) per hour. Then I connected a 3kw load

    to it and it ran for 55 minutes  per quart of fuel, 9% for power, 91% to keep the motor turning.

Go WVO if you could and save a lot of money. Altho, being on a boat, that might be an issue getting, maybe. Hmmm, that'd be interesting to know if it'd be easily accessible.
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#38
Korishan.. I'm more incremental.. WVO is a step a bit far for now.

A lot of people in the tropics, where the boat is now, run their gensets over night to keep the air con on with temps 28-30 deg C. Problem is that most gensets are oversized for that so there is a lot of wasted energy. Not to mention the noise.

On my boat, for example, . the cabin where I sleep will only use about 1/3 of the genset power to keep cool, or less. However with these batteries I can run the genset in the hot part of the day , use say 1/2 to cool the main cabin and the other 1/2 (or whatever is available ) to top up these cells. Idea being that for about 2-3 hours genset usage a day I get 24 hours effective air con availability. That's better climate control AND a substantial savings in diesel.

Jim Jr. I think I see where you are going here.. oversize your panel farm etc.. but the missing link is going to be solar converters etc that are big enough.. Say I do a house battery for 20kWh. If I want to charge that in 6 min I need a 200kW charger.. mmm. but if we ratio that back to charge in an hour its only 20kW of PV and 20kW of charge controller.. maybe more doable. if there were a way to connect the panels directly without the need for a controller may be even more so. Food for thought.
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#39
One thing I've wondered about generators, is if you could either shut off cylinders, or build a custom unit that uses several smaller 1 or 2 cylinder engines. Then as the load increases, the other cylinder(s) start up. They would be clutch engaged so that when 1 isn't running, it's not bogging down the other units with it's mass/compressions.

I agree with the wasted energy problem. The lower the load, the more inefficient the unit becomes. They really shine under heavier loads. Kinda backwards of batteries Tongue
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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#40
(11-11-2018, 03:01 PM)Korishan Wrote: One thing I've wondered about generators, is if you could either shut off cylinders, or build a custom unit that uses several smaller 1 or 2 cylinder engines. Then as the load increases, the other cylinder(s) start up. They would be clutch engaged so that when 1 isn't running, it's not bogging down the other units with it's mass/compressions.

I agree with the wasted energy problem. The lower the load, the more inefficient the unit becomes. They really shine under heavier loads. Kinda backwards of batteries   Tongue

Inverter gen sets do a bit better in that situation, the just run on a lower level but, of course, still make noise...
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