Battery life using inverter

Page 2 - Passionate about caravans & motorhome? Join our community to share that passion with a global audience!
Mar 14, 2005
17,760
3,172
50,935
Visit site
Doing some calculations and it seems a unit drawing 65w off through a Victron 500w pure sine inverter a 95ah battery could last up to 17 hours of the battery is in good nick. Battery capacity = 95Ah x 12V = 1140 Wh. Using the formula to calculate the battery life: Battery life = 1200Wh / 65W ≈ 17.53 hours
There are two things you have overlooked.

Firstly as has been discussed previously in this thread, a battery is rated to have maximum State Of Charge quoted in Amp Hours (Ah) You tell us your battery is a 95Ah battery.

It is recommended that a Lead Acid Battery should only be used to a Depth of Discharge(DOD) of 50%. in your case that means only using 48Ah. If you go below 50% there is a rapidly increasing probability the battery will be damaged or have its working life significantly reduced.

Given this information it points to halving your available run time to about 8.75 hours.

But there is more to bear in mind:

As batteries age, their ability to hold 100% of their stated capacity diminishes. I suggest a Lead Acid battery might lose 10% of its capacity year on year

You would expect a new battery holding 100Ah of capacity should last 100 hours if it was delivering 1 A continuously. If you double the current draw, you might expect the battery to only last 50 hrs. Unfortunately if you increase the current draw the battery has a harder time producing the current, and it actually does reduce its overall capacity and it might only manage 48 hours at 2A. I can't give exact figures as there are so many variables, but if your system is drawing enough current from the battery fo give you 65W which divided by a nominal 12V means it will be drawing 5.4A , then there could be a noticeable reduction in the length of time the battery can drive your TV

I would expect that with all these losses your 17.53 theoretical run time could in practice be down to 7 hours (or less if the battery is not in good condition) , before the battery voltage is too low to drive the inverter.
 
  • Like
Reactions: GUMPY
Jul 18, 2017
12,417
3,493
32,935
Visit site
There are two things you have overlooked.

Firstly as has been discussed previously in this thread, a battery is rated to have maximum State Of Charge quoted in Amp Hours (Ah) You tell us your battery is a 95Ah battery.

It is recommended that a Lead Acid Battery should only be used to a Depth of Discharge(DOD) of 50%. in your case that means only using 48Ah. If you go below 50% there is a rapidly increasing probability the battery will be damaged or have its working life significantly reduced.

Given this information it points to halving your available run time to about 8.75 hours.

But there is more to bear in mind:

As batteries age, their ability to hold 100% of their stated capacity diminishes. I suggest a Lead Acid battery might lose 10% of its capacity year on year

You would expect a new battery holding 100Ah of capacity should last 100 hours if it was delivering 1 A continuously. If you double the current draw, you might expect the battery to only last 50 hrs. Unfortunately if you increase the current draw the battery has a harder time producing the current, and it actually does reduce its overall capacity and it might only manage 48 hours at 2A. I can't give exact figures as there are so many variables, but if your system is drawing enough current from the battery fo give you 65W which divided by a nominal 12V means it will be drawing 5.4A , then there could be a noticeable reduction in the length of time the battery can drive your TV

I would expect that with all these losses your 17.53 theoretical run time could in practice be down to 7 hours (or less if the battery is not in good condition) , before the battery voltage is too low to drive the inverter.
Thank you for your input regarding variables etc, but as mentioned in my first post, it is an 95ah AGM battery. Not sure if that makes any difference as they can discharge a lot more than a LA. If we can get 7- 8 hours out of the battery then all is good. Thanks.
 
Nov 6, 2005
7,451
2,124
25,935
Visit site
Thank you for your input regarding variables etc, but as mentioned in my first post, it is an 95ah AGM battery. Not sure if that makes any difference as they can discharge a lot more than a LA. If we can get 7- 8 hours out of the battery then all is good. Thanks.
"a lot more" is overstating it - an AGM can probably discharge 60% with a conventional Lead-Acid only discharging 50% - so your 95Ah AGM would give 57Ah in practice but if it's at the end of it's primary use it'll be more like 28Ah.
 
Jul 18, 2017
12,417
3,493
32,935
Visit site
As per the attached picture I am not sure what they mean by Minimum Battery Cap? The Victron inverter came with no cables whatsoever.

It seems the customer has to make up the cables? Probably need to buy a 2 metres of 1.5mm cable, 1m of each colour plus a fuse holder and fuse. Unfortunately when purchasing the unit there is no mention that it does not come with the cabling like most other inverters. A bit annoying!

Inverter data.jpg
 
Dec 27, 2022
128
67
635
Visit site
As per the attached picture I am not sure what they mean by Minimum Battery Cap? The Victron inverter came with no cables whatsoever.

It seems the customer has to make up the cables? Probably need to buy a 2 metres of 1.5mm cable, 1m of each colour plus a fuse holder and fuse. Unfortunately when purchasing the unit there is no mention that it does not come with the cabling like most other inverters. A bit annoying!

View attachment 6158
1.5mm is only good if you have a 48v inverter
6 or 4mm minimum is what's needed.
 
Jul 18, 2017
12,417
3,493
32,935
Visit site
I am having a bit of difficulty obtaining the 120A blade fuse and holder. I am not sure if you can get 120A blade fuse. Please can anyone offer any suggestions before I send the unit back. Thanks.
 

JTQ

May 7, 2005
3,356
1,165
20,935
Visit site
"Maxi" blade fuses have "only" a 20 to 100 Amp range.

Two , totalling 120 Amp in parallel?? Edit: I see its not an "approved" technique.

Why impose a "Blade" requirement?
 
Last edited:
Jul 18, 2017
12,417
3,493
32,935
Visit site
"Maxi" blade fuses have "only" a 20 to 100 Amp range.

Two , totalling 120 Amp in parallel??

Why impose a "Blade" requirement?

I am not that familiar with fuses and fuse holders therefore used the term "blade". I am happy to be corrected as a bit unsure of this territory, but need a 120A fuse and holder for the positive cable. Thanks.

I was looking at this and just replacing the fuse holder.
 
Dec 27, 2022
128
67
635
Visit site
Anything over 30amps and I use something like this.

Despite the title it does go to 150amp.
Needs lugs on the cable.
 
Last edited:
Jul 18, 2017
12,417
3,493
32,935
Visit site
Anything over 30amps and I use something like this.

Despite the title it does go to 150amp.
Needs lugs on the cable.
Using the link by JTQ I managed to source the fuse and fuse holder. Next issue is trying to get suitable cable at least 6mm in diameter plus the crocodile clips or clamps. However as the cable may be 2m in length maybe the 10mm would be better? Not sure of search terms to find the correct cable as Amazon doesn't seem to have anything suitable that is at least 1.5m in length although I would prefer 2m.

I must admit I never thought buying an inverter could give me so many complications. LOL! The last time I bought an inverter ti came with all the cables etc.
 
Nov 11, 2009
20,566
6,348
50,935
Visit site
Using the link by JTQ I managed to source the fuse and fuse holder. Next issue is trying to get suitable cable at least 6mm in diameter plus the crocodile clips or clamps. However as the cable may be 2m in length maybe the 10mm would be better? Not sure of search terms to find the correct cable as Amazon doesn't seem to have anything suitable that is at least 1.5m in length although I would prefer 2m.

I must admit I never thought buying an inverter could give me so many complications. LOL! The last time I bought an inverter ti came with all the cables etc.
Are you sure the cable is 6mm diameter that’s a thumping big cable. Could it be 6mm2?

Victron flexible cable can be supplied at 6mm2 and 2.0 m

 
Last edited:
Jul 18, 2017
12,417
3,493
32,935
Visit site
Are you sure the cable is 6mm diameter that’s a thumping big cable. Could it be 6mm2?

Victron flexible cable can be supplied at 6mm2 and 2.0 m

Thanks. Almost got the incorrect size. I looked at the chart and assume it was 6mm and not 6mm squared. As the cable could be up to 2m in length then perhaps 10mm squared would be better. However by the same token it is unlikely we will ever draw as much as 10amps even when using the unit in the caravan?
 
Mar 14, 2005
17,760
3,172
50,935
Visit site
"Maxi" blade fuses have "only" a 20 to 100 Amp range.

Two , totalling 120 Amp in parallel?? Edit: I see its not an "approved" technique.

Why impose a "Blade" requirement?
Paralleling fuses will not increase the protection provided by the biggest fuse in the circuit. Fuses are essential low value resistor's which are designed to heat up as current passes through them. The fuse material has a critical thermal characteristics which will get hot enough to soften and eventually melt the material to break the connection. Fuses designed to carry high currents have a lower conduction résistance than lower current fuses.

When resistors are wired in parallel, the current will always preferentially take the easiest route which will be the fuse with the lowest resistance. This means the high current fuse will carry more than it should and will reach its rupture conditions before the lower current fuses. But as soon a the high current fuse blows and breaks, the current will divert and over rate the lower value fuse causing it to blow virtually instantly. The time for this will be imperceptible to the human eye.
 
  • Like
Reactions: Buckman
Nov 16, 2015
10,629
2,943
40,935
Visit site
I still think, your better with a transistor radio listening to radio 4, and reading a Kindle, under candle light. If you haven't gone to sleep after 4 hours go to a travel lodge. That will kill another few hours.
Total cost cheaper than batteries and inverters.
And less mental stress, for us all
 
Mar 14, 2005
17,760
3,172
50,935
Visit site
I still think, your better with a transistor radio listening to radio 4, and reading a Kindle, under candle light. If you haven't gone to sleep after 4 hours go to a travel lodge. That will kill another few hours.
Total cost cheaper than batteries and inverters.
And less mental stress, for us all
Where's your sense of adventure, and can't you remember the feeling of elation when you survived your first power cut ...........
 
  • Haha
  • Like
Reactions: Hutch and Sam Vimes
Jul 18, 2017
12,417
3,493
32,935
Visit site
I still think, your better with a transistor radio listening to radio 4, and reading a Kindle, under candle light. If you haven't gone to sleep after 4 hours go to a travel lodge. That will kill another few hours.
Total cost cheaper than batteries and inverters.
And less mental stress, for us all
However we are proposing going off grid on one or two this year so inverter will be travelling with us. I apologise for causing you a lot of mental stress, but if you do not like any of my threads as you have hinted on other occasions, no one is forcing you to read them. (y)
 
Nov 11, 2009
20,566
6,348
50,935
Visit site
I still think, your better with a transistor radio listening to radio 4, and reading a Kindle, under candle light. If you haven't gone to sleep after 4 hours go to a travel lodge. That will kill another few hours.
Total cost cheaper than batteries and inverters.
And less mental stress, for us all
Transistor radio. That brings back memories of camping in the Scouts trying to receive Radio Luxembourg, and hoping “Skip” didn’t hear it when doing his nightly rounds as it would be confiscated. It’s amazing how such poor reception became so addictive 😂
 
  • Like
Reactions: RogerL
Jul 18, 2017
12,417
3,493
32,935
Visit site
Transistor radio. That brings back memories of camping in the Scouts trying to receive Radio Luxembourg, and hoping “Skip” didn’t hear it when doing his nightly rounds as it would be confiscated. It’s amazing how such poor reception became so addictive 😂
We had a crystal radio to listen to LM (Lourenzo Marques now Maputo) on shortwave. LM was over 1000 miles north of us! It was the only way we could listen to Beatle music as it was banned from radio stations in South Africa. due to a comment by John Lennon.
 

Sam Vimes

Moderator
Sep 7, 2020
1,674
1,236
5,935
Visit site
When I was the chairman of our Community Council, SSE gave me a number of wind up and solar powered radios for use in power cuts. Nobody was interested in having one.

I played with one for a while then sent it to the charity shop. A couple of other members of the council took one but I don't know that they ever got used.
 
Jul 18, 2017
12,417
3,493
32,935
Visit site
When I was the chairman of our Community Council, SSE gave me a number of wind up and solar powered radios for use in power cuts. Nobody was interested in having one.

I played with one for a while then sent it to the charity shop. A couple of other members of the council took one but I don't know that they ever got used.
We still have a working transistor radio that must be at least 45 years old. It works on either mains or batteries. It has BC, SW1, SW2, SW3 and FM. I think the BC is Standard Broadcast i.e. AM? Surprisingly it does not have medium wave unless that is the BC band?
 

TRENDING THREADS

Latest posts