lithium battery source/price thread

[dreuge]

[QUOTE= redneckrob;2913526
Amp hours (Ah) are a measure of power delivered over time. That battery can supply 170 amps for 1 hour at 12.8V. You seem to be thinking about amps (as opposed to amp hours) which is an instantaneous amount of power. A 700 CCA battery can deliver 700 amps for a very short period of time to start an engine, nothing in reasonable size could deliver that for an hour to make it a 700Ah battery.
I would humbly suggest that batteries and electricity can be very dangerous things. If one is unclear on the difference between amp hours and amps, it points to dozens or hundreds of other important concepts in the field that one may not only not understand but not even know that they don't know exist, any of which can lead to catastrophic consequences for them, their family and guests, and those who put themselves at risk to rescue them. Sorry to be so blunt, but to an electrical engineer that statement is akin to me showing up for your brain surgery and asking the nurse to "hand me the knife"!

""Obviously, we come to the Forum to learn. IMHO, It is then your obligation, as a member of the Forum with the knowledge, to help educate. "
[/QUOTE]

Yes, but the above quote is wrong! An Amp*hr is actually total charge (i.e. current I equals charge Q divided by time t), that is, an Amp*hr is I * t = (Q/t)*t = Q. So assuming constant voltage (typically 12.5 volts), the total energy E = Q * V. Energy is what is important and not power. Power P is energy per time, or rearranged states that energy E = P * t (i.e the Watt * hr) which is also E = ( V * I) * t since power is voltage times current ( E/Q * Q/t = E/t = P) where voltage by definition is energy per charge and current is charge per time.

Yes, using Amp*hrs or Watt*hrs is a bit sloppy, and jumping between the two, i.e., the total charge and total energy, adds more to the mess. In a perfect "constant voltage" world total energy and total charge are related by a constant factor: E = V * Q. But voltage is not constant.

People talk of the mystery of Peukert's law. It's no mystery. It is basically a statement that lead-acid batteries have large internal resistance R. When current flows from a battery some of the energy is lost due to the internal resistance (ie. battery heats up). The energy loss due to resistance is E_loss = I^2 *R (current squared * resistance). The greater the current, the greater the E_loss and smaller the E_usable. That is E_usable = E_battery - E_loss. The problem with batteries is that R is not a constant value.

This is why we have different Amp*hrs ratings at different currents.

The good news is that LiFe batteries have very little internal resistance. So there is hope that the standards will move to being less sloppy. I just hope we don't start using something stupid like equivalent amp hours (i.e. eAmp*hrs) but given the light bulb experience, we may be doomed to stupidity!.

[john61ct]

Wh or Ah is the energy unit to use per unit of time.

Amps and watts are power, rate of flow.

Amps per hour is ambiguous, really should not be used at all.

[surf_km55]

Originally Posted by Shrew

I love 'crowd funded' research. It feels a lot like. " I don't want to do my homeworl, just tell me what you found out when you did your research".

Jajajajajajajajaja, yer killin' me over here.
Damn, tough crowd.


On a lighter note, I have a single 170 AH LiFePO4 on tap as a separate house bank for watermaker, induction cooktop, & small freezer. Daily AH total consumption is 105 AH assuming watermaker runs for 3 hours.
Pre-tax cost: $1350.
Weight: 21kg/46.3lbs



https://www.renogy.com/renogy-lithiu...12-volt-170ah/

[dreuge]

Originally Posted by john61ct

Wh or Ah is the energy unit to use per unit of time.

Amps and watts are power, rate of flow.

Amps per hour is ambiguous, really should not be used at all.

Let me correct this:

An Ampere is standard unit for electrical current. It is defined as 1 Amp = (1 coulomb of charge)/(1 second). This comes directly from the defining equation for current = charge per time.

A Wattt is the standard unit for power. It is defined as 1 Watt = (1 Joule of energy)/(1 second). This come directly from the defining equation for power = energy per time.

Amps per hour is NOT ambiguous. It is a unit (albeit unconventional) for charge. The conventional unit for charge is the Coulomb. 1 Amp*hr = [(1 Coulomb)/(1 second)] * ( 1 hour) = [(1 Coulomb)/(1 second)] * ( 1 hour) * (3600 seconds/hour) = (3600 Coulombs). Yes, 1 Amp*hr = 3600 Coulombs.

I agree it is a sloppy unit. It is like measuring mass with units of mass flow * time: i.e., lb/s * hr where 1 kg/s *hr = 3600 kg. Not that useful unless you are weighing elephants (average elephant mass = 1.5 kg/s *hr).

[Two Skippies]

These batteries from iTECH in Australia are claimed to be “drop in” replacements for Lead Acid batteries. I contacted the suppliers regarding solar controllers etc and they told me nothing needs to be changed, just swap the batteries over.

I’m certainly a dummy regarding electrics, and I haven’t as yet purchased these batteries.
If anyone can tell me why I shouldn’t try them I’d be happy to know.
This is in response to OP.
Cheers,
Twoskippies.

[john61ct]

I just meant that "amp hour" is precise

many people claim (does wiki still?) that Ah means "amp per hour"

which to me is not precise.

An amp as an average current flow, running **for an hour** or **over the period** of an hour, yes that is precise.

Noobs see a device nameplate rating of 4A draw at say nominal 12V, and think "that means it will use just under 100Ah every 24 hours".

In fact, power demand may vary greatly within each hour due to many factors, ambient temperature affects duty cycles for example, so in reality that device only uses 25-40Ah per day in moderate circumstances.

Using "amps per hour" or "watts per hour" is just plain confusing, and IMO should be struck from polite society.

[john61ct]

Originally Posted by Two Skippies

These batteries from iTECH in Australia are claimed to be “drop in” replacements for Lead Acid batteries

Well of course you can do that, and I'm sure they will last past the warranty period. Well not sure, but the odds are good if it's under five years.

No idea how their quality compares to say Battle Born.

Just know they would last **a lot** longer if their infrastructure is optimized for LFP rather than that expedient compromise and specious marketeering claim that they are "just like lead".

Another factor is, that if they have internal protective BMS circuitry built in, that will likely impose limits on C-rates that you may not be aware of.

You may also not have access to per-cell voltages to check and see if they're going out of balance.

There may be no communications between their internal BMS and your other control / monitoring gear.

Their BMS may suddenly take the battery offline without warning, so make sure that's not the **only** buffering device on the buss with devices like alternators or expensive & sensitive electronic devices that don't appreciate the resulting load dumps, massive spikes and surges.

Finally, on what basis do you judge that they have good quality control, who actually makes their cells, will they last nearly as long as say Winston or CALB or GBS?

So if you do give them a try, do please let us know how things go, it will take many years for a new entrant to establish a good (or bad) reputation, and that happens one user report at a time.

[BruceS]

2Skips..
There has been a lot of discussion around the sudden appearance of these "drop ins" in the Australian market lately that you are probably aware of.
'Drop' in or maybe more accurately 'replacement' of lead acid batteries is the trick.
If you use them the same as your old batteries.
That is charging at the same 'pathetic' rate and max draw at the same poor rate.
If that is so.... what advantage are you gaining?
Ask the seller what he recommends as max rates? (in & out)
......... Silence please John

[Reefmagnet]

Originally Posted by Two Skippies

These batteries from iTECH in Australia are claimed to be “drop in” replacements for Lead Acid batteries. I contacted the suppliers regarding solar controllers etc and they told me nothing needs to be changed, just swap the batteries over.

I’m certainly a dummy regarding electrics, and I haven’t as yet purchased these batteries.
If anyone can tell me why I shouldn’t try them I’d be happy to know.
This is in response to OP.
Cheers,
Twoskippies.

Just this morning I've been comparing these batteries to the "AllSpark". The iTech seem good, aside from continuous current output. I like the AllSpark for their higher outputs and I really like the bluetooth model they have although longevity in a marine environment might be another thing. On the downside I'd prefer 120Ah to 100 AH and the weight of the battery seems a bit light on (I, wrongly or rightly, think battery weight is a pretty good indication of the true capacity and robustness of a battery).


Be that as it may, this is an interesting grab from their website on the use of a regular charger

[sparrowhawk1]

[emoji23]

[john61ct]

Such honesty is a good sign

[KTP]

Honestly from an engineering standpoint I do not see a reason why a drop in lithium battery cannot be made to stand up to nearly any charger.

You should not be able to kill a correctly designed drop in lithium battery from overcharging. If you can, it is just poor engineering on the manufacturer's part.

[BruceS]

eggsactly & that is the problem/warning!!

[john61ct]

Wut?

Maybe if you mean wrt BMS, but of course it's easy to turn a set of bare cells into instant scrap.

Maybe .05% of BMS have any kind of low temperature protection for example.

And if you want to charge at 2C and discharge at 5C, are willing to set up the infrastructure to do so safely, and are willing to only get a few years out of them, the battery can handle that just fine, but no drop-in will allow it.

It's easy to murder a lead bank costing $15000 too, why should LFP be any different?

[KTP]

I meant drop-in, not bare cells.

Again, referring to the Trojan Trillium, they protect against everything you mention, disconnecting the battery from the circuit in some of the situations to protect it. They even monitor the temperature and reduce the charging rate at lower temperatures and then totally prevent charging if the temp is too low. Top notch stuff.

Except their CANbus implementation doesn't allow setting the battery CAN address, so they get a fail