Trying to understand amp hours???

[Dee]

Hi , I'm new to this forum and I'm trying to get my head around amp hours for battery banks, I'm buying a 48v 840ah lead acid battery, the guy selling it to me said he can put in a link to the bank to make it 24v 1680ah, that makes since to me but is there any point in doing that?
Will I get more amp hours when it is changed down from 48v to 24v?
My brain says what ever amp hours is drawn-used will be the same?
I'd rather use 48v as it is a we bit more efficient because it is at higher voltage But I'm really looking for the most amp hours I can get to have the cottage have enough power.
PS I know that you can only use about 50% of the amp hours of a lead acid battery.
Any help is welcome ?

 

[gnubie]

The total power in the battery, watt hours (amps x volts), remains the same. Thinking of things in terms of watt hours makes it easier.

*edit to add more about amp hours*
Amp hours is still something to keep in mind but from a how high a load can I throw at this sucker point of view. Lead acid batteries tend to sag quite a bit under high loads, if your load has to suck a lot of amps from the battery at a given voltage you need an appropriate amp hour rating to be able to hold the voltage up reasonably across the full state of charge that you plan on using. You can pull 200 amps from a 100 AH battery but it's going to suffer doing it, and your output voltage will fall quite a bit while yo do it.

 

[GMB]

Agree, watt hours are much easier to comprehend in my opinion.

So your 48v, 840 ah battery has (48x840) 40,320 watt hours.
If it was at 24 volts, 1680 ah, it still has (24x1680) 40,320 watt hours.

So you could power a 1000 watt device for approximately 40 hours with either configuration. But not in reality, because like you said, 50% discharge and inverter loss, etc., would need to be accounted for. But just some general math to help understand the concept.

 

[John Frum]

@Dee our fearless leader has got your questions covered.

If you have follow up questions after watching this video we got you.

 

[Gazoo]

IMO that's one of Wills best videos if not the best. It was a refresher for me and was refreshing. Anyone new getting into any kind of electrical/electronics related DIY needs to watch that video.

 

[Dzl]

Hi , I'm new to this forum and I'm trying to get my head around amp hours for battery banks, I'm buying a 48v 840ah lead acid battery, the guy selling it to me said he can put in a link to the bank to make it 24v 1680ah, that makes since to me but is there any point in doing that?
Will I get more amp hours when it is changed down from 48v to 24v?
My brain says what ever amp hours is drawn-used will be the same?
I'd rather use 48v as it is a we bit more efficient because it is at higher voltage But I'm really looking for the most amp hours I can get to have the cottage have enough power.
PS I know that you can only use about 50% of the amp hours of a lead acid battery.
Any help is welcome ?

In my opinion, the best beginner friendly orientation to electricity and electrical units of measurement on a conceptual level is this one from Solid State Workshop:

There are others (like Will's video posted above) that outline the basics and give you all the info you need to know, and are quite helpful. But the video from Solid State Workshop is the first video where everything 'clicked' and started to feel intuitive to me on a conceptual level.

 

[Cal]

Agree, watt hours are much easier to comprehend in my opinion.

So your 48v, 840 ah battery has (48x840) 40,320 watt hours.
If it was at 24 volts, 1680 ah, it still has (24x1680) 40,320 watt hours.

AH is easier to understand. It is a battery specification. WH is only an approximation since battery voltage decreases as it is discharged.

AH increases with parallel cells, but voltage remains the same.
AH remains constant with cells in series, while voltage increases.

 

[DaWiFiGuy]

Hi , I'm new to this forum and I'm trying to get my head around amp hours for battery banks, I'm buying a 48v 840ah lead acid battery, the guy selling it to me said he can put in a link to the bank to make it 24v 1680ah, that makes since to me but is there any point in doing that?
Will I get more amp hours when it is changed down from 48v to 24v?
My brain says what ever amp hours is drawn-used will be the same?
I'd rather use 48v as it is a we bit more efficient because it is at higher voltage But I'm really looking for the most amp hours I can get to have the cottage have enough power.
PS I know that you can only use about 50% of the amp hours of a lead acid battery.
Any help is welcome ?

The simple way that I think of it is that you can store enough energy in that battery bank to run a 48V load pulling 1A (amp) for 840 hours or a 24V load pulling 1A (amp) for 1680 hours. Like you mentioned you are probably only going to be able to pull those loads for half the amount of time (AH).

Have you settled on a charger/inverter solution? If you have, that might be the deciding factor for using 48V or 24V. It seems like the majority of projects that I see for running a cottage are using 48V systems.

I am far from being an expert in any of this, so take what I say with a little skepticism.

 

[RickP]

One advantage of a higher voltage battery system is a lower amperage to supply the same loads. This requires less heavy wiring, and can be a big cost savings in building a system. If your system, including wiring and fuses/breakers, is built for 48v, there is no advantage (and possibly some danger) in going to 24v batteries, even if everything else would work (it won’t).

No idea why the sales person was muddying the water. Listen to your brain, it’s right.

 

[boondox]

The total power in the battery, watt hours (amps x volts), remains the same. Thinking of things in terms of watt hours makes it easier.

edit: Whoa! Blew that one! Talk about a Freudian slip!

Yes! I really wish people would use amp hours watt hours. For example, in my signature you don't need to know what voltage I am running to know what my system capacities are. Amps only tell part of the story. It is a bit of a pet peeve of mine.

So is "solar generator". A generator is " a dynamo or similar machine for converting mechanical energy into electricity. " But I guess that ship has sailed too.

 

[RickP]

So is "solar generator". A generator is " a dynamo or similar machine for converting mechanical energy into electricity. " But I guess that ship has sailed too.

Long sailed. It's one of those things that, while not perfectly correct in the electrical engineering sense, has a different meaning to the common guy on the street. Both are converters of one thing to another. Don't let it keep you up nights.

 

[boondox]

Long sailed. It's one of those things that, while not perfectly correct in the electrical engineering sense, has a different meaning to the common guy on the street. Both are converters of one thing to another. Don't let it keep you up nights.

I'll try. But is it ok if I yell at the kids to get off my lawn?

 

[RickP]

I'll try. But is it ok if I yell at the kids to get off my lawn?

Oh yeah, that’s always acceptable!

 

[DaWiFiGuy]

... It is a bit of a pet peeve of mine.

So is "solar generator". A generator is " a dynamo or similar machine for converting mechanical energy into electricity. " But I guess that ship has sailed too.

"Wind generator", but I digress to much. Time to go yell at some kids on my lawn.

 

[Forbisher]

. It is a bit of a pet peeve of mine.

So is "solar generator". A generator is " a dynamo or similar machine for converting mechanical energy into electricity. " But I guess that ship has sailed too.

A pet peeve of mine is saying a solar generator is only a battery.
a Solar Generator is a "battery"
And a MPPT / PWM solar charge controller
And an Inverter
And a built in battery charger from AC and DC
All controlled by an intergrated power meter with voltage and current protections plus DC outputs in a compact package.
That is the definition of a solar generator which is designed to be charged from photovoltaic panels and other sources to compete with combustion generators.
When solar panels are combined with a solar generator that is the intended complete functionality.

 

[Dee]

Thanks everyone for your reply, I have learned a lot from this ?

 

[Dee]

The simple way that I think of it is that you can store enough energy in that battery bank to run a 48V load pulling 1A (amp) for 840 hours or a 24V load pulling 1A (amp) for 1680 hours. Like you mentioned you are probably only going to be able to pull those loads for half the amount of time (AH).

Have you settled on a charger/inverter solution? If you have, that might be the deciding factor for using 48V or 24V. It seems like the majority of projects that I see for running a cottage are using 48V systems.

I am far from being an expert in any of this, so take what I say with a little skepticism.

Hi thanks for the info, I'm thinking to get the 5kw 48v all in one inverter that is on the web site: (see attached pic )
It says it has 2 X 80a mppt so I take it I can add 160a of panels to it?

Next thing for me to wrap my brain around is how many panels it will take? I'm thinking of using 14 X 310w 39v 5amp panels: ( see attached pic )

Thanks again guys, looking forward to your reply's

 

[GMB]

This is a .pdf of the LV5048. It shows that 4000 watts of solar can be connected to each mppt - so 8000 watts total. https://www.mppsolar.com/v3/catalogs/split phase LV5048.pdf

For how to connect the panels and the math behind series and parallel connections - watch this video.

 

[Dee]

This is a .pdf of the LV5048. It shows that 4000 watts of solar can be connected to each mppt - so 8000 watts total. https://www.mppsolar.com/v3/catalogs/split phase LV5048.pdf

For how to connect the panels and the math behind series and parallel connections - watch this video.

Hi, thanks for the info, I found this inverter : ( please see attached pic ) would it do my job? It is much cheaper, thank you.

 

[Dee]

This is a .pdf of the LV5048. It shows that 4000 watts of solar can be connected to each mppt - so 8000 watts total. https://www.mppsolar.com/v3/catalogs/split phase LV5048.pdf

For how to connect the panels and the math behind series and parallel connections - watch this video.

Sorry to be a pain , I can see what the inverter voltage cutoff is with this inverter, ie when the batteries ( lead acid ) go down in volt at what volt will the inverter stop making power, is it 48v?
Thanks