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albertramsbottom

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Oct 6, 2021
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Hi

Please can someone point me the right direction to understand the difference between AH and WH at different voltages

I ask because people like Tesla describe their battery packs in WH such as 90KWH. Now I understand that WH is probably the best form of description for solar and EV systems rather than AH, however, when ever you purchase batteries they are described in AH

I understand this but what are the maths to work out AH to KWH on differing voltages?

A Tesla with a 90KWH battery pack is how many AH's at 3.2, 6 12 24 and 48V for instance?

Also what advantages does 48V have over a system that might be 12V or 24V? is it an inverter benefit?

Thanks for any help

Oh and after reading some reviews around I have been looking at these. Are they too good to be true? 280aH for x 4 3.2V for £380. Seems extremely good value for a lithium battery with 5000 cycles
 
Curious if you’ve already watched the wiring basics for newbies on YouTube that Will Prowse put out. That overviews these items.I recommend it, plus this is covered in ‘resources for beginners’ in reading material.

Watts = Volts x Amps
So a little algebra works up your answer

Say you have a 100Ah 12V battery.
Watts get solved for. W= 100 * 12= 1200; 1200Wh or 1.2kWh. Amps describe current, watts describe energy, voltage is power.
 
Yes I have watched loads of youtubes but all you get is loads of experts arguing that lithium ion or lead acid or lithium titanate is best. Currently if weight is not an issue then the best batteries I have found are Lead Acid - Trojans 6V 620AH 17 year 12000 cycles for around £500

I understand the OMS law but was just confused around reverse engineering it from KWH if you do not know the voltage. For instance the Tesla 90KWH battery pack. How many AH this is? I suppose I am asking if anyone knows what voltage these run on. If I know I can work out the AMP Hours :)

Thanks for your help

I have looked at some the beginner resources but found them a little lacking, in areas such as having a legend and real world voltages for the cell configurations.

I also need to understand what advantages 12, 24 or 48V systems have. What are the pros and cons
 
Tesla battery IIRC runs about 300 to 400 volts depending on level of charge. Call it 350 volts and 90kWh becomes 257 ah.

The lower the voltage the more amps required to get the same wattage. The higher the amps the bigger the wire and it goes exponential. Typically 12v is best to stay at or below 2000 watts.
 
I understand the OMS law but was just confused around reverse engineering it from KWH if you do not know the voltage.
KWH = kilo watt hours
Its a measure of power over time.
watts = volts * amps.
You need to know either volts or amps to compute the other.

amps = watts / volts
volts = watts / amps
 
Yes I have watched loads of youtubes but all you get is loads of experts arguing that lithium ion or lead acid or lithium titanate is best. Currently if weight is not an issue then the best batteries I have found are Lead Acid - Trojans 6V 620AH 17 year 12000 cycles for around £500

I understand the OMS law but was just confused around reverse engineering it from KWH if you do not know the voltage. For instance the Tesla 90KWH battery pack. How many AH this is? I suppose I am asking if anyone knows what voltage these run on. If I know I can work out the AMP Hours :)

Thanks for your help

I have looked at some the beginner resources but found them a little lacking, in areas such as having a legend and real world voltages for the cell configurations.

I also need to understand what advantages 12, 24 or 48V systems have. What are the pros and cons
If you buy prismatic cells from China they cost about the same as lead acid. lead acid you can only cycle 50% vs lithium 100% you could build a 300 ah battery for give of take 1k. You're much better off going with the higher voltage like 48v to save money on wire and you can push a lot more wattage.
 
Currently if weight is not an issue then the best batteries I have found are Lead Acid - Trojans 6V 620AH 17 year 12000 cycles for around £500

Curious: where did that 12000 cycle number come from? On their website they have cycle graphs for all their batteries and the most I can find is their Industrial deep cycle flooded line which seems to be able to do more that 7000 cycles - at 20% depth of discharge. At 50%, it drops to 3500 cycles.
 
KWH = kilo watt hours
Its a measure of power over time.
watts = volts * amps.
You need to know either volts or amps to compute the other.

amps = watts / volts
volts = watts / amps
If you buy prismatic cells from China they cost about the same as lead acid. lead acid you can only cycle 50% vs lithium 100% you could build a 300 ah battery for give of take 1k. You're much better off going with the higher voltage like 48v to save money on wire and you can push a lot more wattage.
smoothjoey
Thanks for the Ohms law clarification

Mudd

Those Trojans can go way less the 50% but obviously degrade but they are some of the best on the market for lifespan and cycles. 6500 cycles @30% discharge and 3000 cycles at 50%. I believe this to be better price per Amp/KWH than any lithium battery I have found. The only issue is weight and size so no good for campers
 
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Curious: where did that 12000 cycle number come from? On their website they have cycle graphs for all their batteries and the most I can find is their Industrial deep cycle flooded line which seems to be able to do more that 7000 cycles - at 20% depth of discharge. At 50%, it drops to 3500 cycles.
Yes sorry good question, I saw it yesterday but cant find it now. I am seeing 12000@20% and 2000@80% but if you consider price point per KWH these are pretty impressive

 
If you buy prismatic cells from China they cost about the same as lead acid. lead acid you can only cycle 50% vs lithium 100% you could build a 300 ah battery for give of take 1k. You're much better off going with the higher voltage like 48v to save money on wire and you can push a lot more wattage.
Thanks

I have been looking at this and at 48 volt, if I use lithium will save on loads of stuff apart from the cells, the ones I have been looking at are 3.2V 280AH - will need a shed load for 48V
 
7500 cycles @50% discharge and 3000 cycles at 80%.

This is their top of the line "Solar Industrial Flooded":


From their graph, at 80% depth of discharge you're looking at 2000 cycles.

Let's take their best capacity rate (the 100 hour one, and I'll give you 100% DoD at 2000 cycles), you can get 3.66kWh from their SIND 06 610. Cost of this battery: €600 I could find.

If you DIY a 4-ish kWh battery with 4 x 280Ah LiFePO4 cells this sets you back somewhere around €600 as well. You need a BMS as well, so add €60.

I'd say you're pretty close to the same cost, and you don't have to water them :)
 
OK what about these
https://www.aliexpress.com

Completely safe? 25000 cycles or around 50 years and can be fast charged and discharged in 10 minutes o_O

Yes, LTO is great (if you can work with the voltage range they operate at), but a lot more expensive. Also beware of some of the Aliexpress sellers selling these. Best to get them from Yinlong directly.
 
To further the learning process, units should be written correctly.

A - amps. Named after André-Marie Ampère.
V - volts. Named after Alessandro Volta.
W - watts. Named after James Watt.
h - hours
k - kilo (SI prefix for 1000)

So kilowatt-hours is kWh. And amp-hours is Ah, etc.

While in most cases, at least on this forum, using the wrong case for a unit has little impact and is generally understood, other than driving me nuts :), getting the case wrong can be life threatening. For example:

1mW = 1 milliwatt or 0.001 watts
1MW = 1 megawatt or 1000000 watts

You don't want to get those wrong.

Impress your friends and random Internet strangers by writing your units correctly.
 
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have been looking at are 3.2V 280AH - will need a shed load for 48V
You have not mentioned how much power, (as in watt hours), you need each day. So all this talk about charge cycles, battery voltage and the same is all back seat to what your system needs to provide.
Have you done an energy audit?
An energy audit will most likely answer most of your questions you have asked.
 
You have not mentioned how much power, (as in watt hours), you need each day. So all this talk about charge cycles, battery voltage and the same is all back seat to what your system needs to provide.
Have you done an energy audit?
An energy audit will most likely answer most of your questions you have asked.
Interesting you should say that as I am thinking in the opposite direction. Lots of people audit their current use and decide on that but I am starting from scratch so my energy audit will be what my system can support. I will then if needed make it larger. So no AC, No tumble dryer, no dish waster, gas shower, gas oven, gas hob, no electric kettle, wood heating etc. So my system will support the minimum I can get away with. Whilst I am in to saving the planet this is because I haven't got a supply on the land I have brought and never will
 
To further the learning process, units should be written correctly.

A - amps. Named after André-Marie Ampère.
V - volts. Named after Alessandro Volta.
W - watts. Named after James Watt.
h - hours
k - kilo (SI prefix for 1000)

So kilowatt-hours is kWh. And amp-hours is Ah, etc.

While in most cases, at least on this forum, using the wrong case for a unit has little impact and is generally understood, other than driving me nuts :), getting the case wrong can be life threatening. For example:

1mW = 1 milliwatt or 0.001 watts
1MW = 1 megawatt or 1000 watts

You don't want to get those wrong.

Impress your friends and random Internet strangers by writing your units correctly.
Proper case from now on

A - amps. Named after André-Marie Ampère.
V - volts. Named after Alessandro Volta.
W - watts. Named after James Watt.
h - hours
k - kilo (SI prefix for 1000)

So kilowatt-hours is kWh. And amp-hours is Ah, etc.
 
my system will support the minimum I can get away with
I respect that BUT with the 20-30-year lifespan of your solar investment a little more now to increase convenience and ease is really no big expense over time, AND you have headroom to use vacuum, tools- and my joy- an electric fridge and coffeemaker.

Not everything modern is eschewable luxury. Aged out they’re downright cheap and good for the planet, really.
 
So no AC, No tumble dryer, no dish waster, gas shower, gas oven, gas hob, no electric kettle, wood heating etc. So my system will support the minimum I can get away with. Whilst I am in to saving the planet this is because I haven't got a supply on the land I have brought and never will

So, my goals were somewhat similar, however I did not want to give up luxuries such as proper lighting, a coffee maker, washing machine, etc. Cooking on gas, yes, because I like cooking and gas is the best (I know, induction - which I use in summer when I have excess power, but still), heating with wood, yes, because that's an easily accessible energy source for me. However with just a bit of panning you can have the cake and eat it too: a large enough, expandable system that you can grow as and when required, without putting you in a box where future expansion basically requires a complete replacement.
 
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