Smart Gauge and Batteries again!

[Keeping Up]

Do extension leads have an effect on how many amps an item uses , just out of interest?

 

No - unless they are exceptionally long and/or thin

[Joshua]

Your loads are small enough to make almost no difference. On a 330Ahr battery bank, a 10 amp load will be dropping the at rest voltage by around 0.02 volts. Not worth worrying about.

 

Gibbo can you please confirm those figures. As you know I am having a few of my own battery problems. I began a lengthy test yesterday, after a full charge and 5 hours of use last night (all low loads) I shut down everything except the fridge (consumes about 1amp an hour) last night and noted this morning a voltage reading of 12.59V.I then applied a 7.5A load and the voltage dropped to 12.38, when I turned everything off again it recovered in about 1 hour to 12.57.

 

In other words my small load of 7.5A dropped my voltage compared with the at rest voltage by more than 0.2v not 0.02!

 

Should it not drop by more than .02v?

 

Joshua

PS What sort of load would it have to be to drop the voltage by .2v?

Edited September 21, 2012 by Joshua

[lewisericeric]

That's interesting Joshua as because of whati was saying that would mean my 'resting' voltage would have been higher than 12.40-45 meaning my batteries couldn't be on 67 if that's the case?

[Gibbo]

So r my batteries knackered or summat?! Only had em since march. Kept water topped up n never really let em drop below 70 only in rare cAses like last night.

 

Either that or you have some other loads that you're not aware of.

 

Do extension leads have an effect on how many amps an item uses , just out of interest?

 

Not to any noticable effect.

[lewisericeric]

But they have to be significant loads then?? None that I can think of only regulators for the solar panels and wind turbine and they wouldnt be taking significant loads from the batteries?

[Gibbo]

Gibbo can you please confirm those figures. As you know I am having a few of my own battery problems. I began a lengthy test yesterday, after a full charge and 5 hours of use last night (all low loads) I shut down everything except the fridge (consumes about 1amp an hour) last night and noted this morning a voltage reading of 12.59V.I then applied a 7.5A load and the voltage dropped to 12.38, when I turned everything off again it recovered in about 1 hour to 12.57.

 

In other words my small load of 7.5A dropped my voltage compared with the at rest voltage by more than 0.2v not 0.02!

 

Should it not drop by more than .02v?

 

Joshua

PS What sort of load would it have to be to drop the voltage by .2v?

 

Think about it...

 

This all assumes there is no surface charge which there won't be in the above case.

 

If a load of 7.5 amps drops the voltage by 0.2 volts from the resting voltage, what would a load of 15 amps do to it? 0.4 volts obviously.

 

30 amps 0.8 volts.

60 amps 1.6 volts.

120 amps 3.2 volts.

 

So you reckon a current draw of 120 amps will drop the voltage by 3.1 volts? On a large bank of batteries?

 

How on earth does a single battery manage a cranking rating of (typically) 650 amps without the voltage falling below 10 volts?

 

I just put a 10 amp load on a single battery. The voltage fell by 0.07 volts. 4 batteries in parallel would (obviously) drop by a quarter of this.

 

But they have to be significant loads then?? None that I can think of only regulators for the solar panels and wind turbine and they wouldnt be taking significant loads from the batteries?

 

It sounds like your batteries are getting tired then. If it's any consolation I bough a brand new leisure battery some time ago and totally destroyed it by deep discharging it. It took about 48 hours. After 2 full discharges it had lost 30% of its capacity. Yours are several months old. I've seen batteries destroyed under normal use in a matter of weeks.

 

I'm currently working on a new battery monitor and part of the algorithm results in it calculating the state of health of the batteries. It uses it internally. For the commercial and end user version we've made the decision not to display that data. There's no way to get at it, because we know we will get bombarded with technical calls because no one ever believes how knackered their batteries are. People are happy to blame a battery monitor that tells them their batteries are knackered, but rarely accept that the problem might actually be the batteries themselves.

[lewisericeric]

So what else could I have done to prevent early death of the batteries. This is shocking! Most people I know have batteries years and don't see discharges like this.??

 

Only once did the batteries drop to the 50% range and other than that they've never been lower than around 70

Edited September 21, 2012 by lewisericeric

[Paul C]

So what else could I have done to prevent early death of the batteries. This is shocking! Most people I know have batteries years and don't see discharges like this.??

 

Only once did the batteries drop to the 50% range and other than that they've never been lower than around 70

 

Perhaps the batteries were already damaged by the time they were sold to you, ie they became discharged in between manufacture and their being sold. Its possible....what's the shelf life of batteries? How many stockists periodically recharge them? etc

[Gibbo]

So what else could I have done to prevent early death of the batteries. This is shocking! Most people I know have batteries years and don't see discharges like this.??

 

Only once did the batteries drop to the 50% range and other than that they've never been lower than around 70

 

Can you hazard a guess at how many cycles they've done? To what average depth of discharge?

 

Have they ever been equalised? What's your normal charge voltage?

 

How is your SmartGauge wired up? Does it go directly to the batteries or is it connected to bus bars or something?

[lewisericeric]

Batts at 100% after engine being on.... Voltage is 12.8 - 12.85 with tv on and fridge still on.

 

Switch my 25w lamp on and the voltage immediately drops to 12.75-12.80......??????

 

We only properly came off shoreline In June when we left our marina.... They usually drop to no less than 70-75 most nights.... And charged from the solar panels each day.

 

So say 120 cycles since June?

 

I find my shoreline fridge guzzles a lot. They claim on the website that it used only 0.94 amps. No way!!! I estimate it must be about 3-5. Easily

[Gibbo]

But what is your actual charge voltage?

 

Have they ever been equalised?

[smileypete]

So what else could I have done to prevent early death of the batteries. This is shocking! Most people I know have batteries years and don't see discharges like this.??

 

Only once did the batteries drop to the 50% range and other than that they've never been lower than around 70

lewisericeric, you have 'OSoCD' - Obsessive State-of-Charge Disorder!

 

One way the symptoms are manifested is continual compulsive button pushing on your Smartguage!

 

Just remember, boat batts are usually in one of three states of charge:

 

1. 
    
   
2. Almost but not quite fully charged
   
3. Somewhere around enough charge
   
4. Almost flat as a pancake
   

As long as you avoid the last one and see the first one here and there, you'll do fine.

 

cheers, Pete.

~smpt~

Edited September 21, 2012 by smileypete

[Joshua]

Think about it...

 

This all assumes there is no surface charge which there won't be in the above case.

 

If a load of 7.5 amps drops the voltage by 0.2 volts from the resting voltage, what would a load of 15 amps do to it? 0.4 volts obviously.

 

30 amps 0.8 volts.

60 amps 1.6 volts.

120 amps 3.2 volts.

 

So you reckon a current draw of 120 amps will drop the voltage by 3.1 volts? On a large bank of batteries?

 

How on earth does a single battery manage a cranking rating of (typically) 650 amps without the voltage falling below 10 volts?

 

I just put a 10 amp load on a single battery. The voltage fell by 0.07 volts. 4 batteries in parallel would (obviously) drop by a quarter of this.

 

 

 

Thanks, I have a bigger problem than I realised.

 

Joshua

[Gibbo]

Thanks, I have a bigger problem than I realised.

 

Don't instantly jump to doom conclusions.

 

Is your voltemeter wired directly to the battery bank? You might find you're actually measuring the voltage drop of cables, switches, fuse holders, shunts etc.

[Theo]

Lewisericeric,

 

You say you find it difficult to understand, but you have managed to get the basic approach exactly right. You may find it easier if you spend some time thinking about the terms Amp and Amp-hour, and getting them straight in your mind. Then whenever you do the maths (or myths) make sure you use the correct terminology throughout for not only will it make things clearer, it will also highlight any points where you have made any errors.

 

The rate at which anything consumes current, is measured in amps. Thus in your example your iPod takes 2 amps (not 2 amps an hour or anything else) and your 25 watt lamp also takes 2 amps.

 

If you multiply the current in amps by the time in hours you get the total amount of energy that has been taken, in amp-hours. So drawing current at a rate of 2 amps for a time of 5 hours means you have taken 2 amps x 5 hours = 10 amp-hours. That is also why battery capacities are quoted in amp-hours, which indicates how much energy you can take rather than how much current you can take.

 

 

The Ampere-hour (A-h) is not a measure of energy. It is a measure of charge. You have to multiply A-h by volts for energy. So 4A for 2hrs at 12 volts = 96 watt-hours

 

 

 

Think about the units again, until you have them clearly defined, and you will definitely find it easier. Not that the people at Shoreline have not been able to understand this, and they are completely wrong when they quote the current taken by their fridges in "amps per hour" - that is a complete nonsense, they just mean "amps".

 

You have worked out your numbers correctly, as far as I can see at first glance. My suspicions are that your batteries were not holding 330 amp-hours when you thought they were full. This could be because they are not brand-new, and so their capacity isn't what it was; or it could be because they weren't actually at 100% (the Smartgauge site does say it won't be completely accurate when the batteries are charging), or more likely it is a combination of the two. Unfortunately a voltage reading, when the battery is either charging or discharging (or has been doing so within the previous few hours) is likely to be meaningless.

 

but the drift of the argument is fine.

 

Nick

 

 

[Joshua]

Don't instantly jump to doom conclusions.

 

Is your voltemeter wired directly to the battery bank? You might find you're actually measuring the voltage drop of cables, switches, fuse holders, shunts etc.

 

I’ll need to check, it’s a victron monitor supplied with its own shunt and I had assumed it was wired into that.

 

 

 

 

Joshua

 

 

[nicknorman]

The Ampere-hour (A-h) is not a measure of energy. It is a measure of charge. You have to multiply A-h by volts for energy.

Harsh ... But true!

[Keeping Up]

The Ampere-hour (A-h) is not a measure of energy. It is a measure of charge. You have to multiply A-h by volts for energy. So 4A for 2hrs at 12 volts = 96 watt-hours

 

 

 

but the drift of the argument is fine.

 

Nick

 

 

 

Absolutely correct Nick, well spotted. I must grovel and make my apologies for letting my typing fingers get ahead of my brain.

[Gibbo]

Absolutely correct Nick, well spotted. I must grovel and make my apologies for letting my typing fingers get ahead of my brain.

 

However, as the voltage doesn't change too much during discharge, amp-hours are analogous to energy. Which is the simplification amp-hour counters work on. It's not, of course, strictly true but often considered close enough for battery monitoring.

 

It would result in a perfectly working amp-hour counter disagreeing with the a perfectly working monitor that works on true energy (as opposed to amp-hours) disagreeing by up to the difference in voltage ratio between full and flat.

 

Further, If the discharge is graphed, with a constant load (not constant current - i.e. same energy discharge throughout the discharge) an amp-hour counter will show a curved graph as the discharge current will increase as the voltage reduces.

 

It's covered on my website somewhere.

[Theo]

However, as the voltage doesn't change too much during discharge, amp-hours are analogous to energy. Which is the simplification amp-hour counters work on. It's not, of course, strictly true but often considered close enough for battery monitoring.

 

It would result in a perfectly working amp-hour counter disagreeing with the a perfectly working monitor that works on true energy (as opposed to amp-hours) disagreeing by up to the difference in voltage ratio between full and flat.

 

Further, If the discharge is graphed, with a constant load (not constant current - i.e. same energy discharge throughout the discharge) an amp-hour counter will show a curved graph as the discharge current will increase as the voltage reduces.

 

It's covered on my website somewhere.

 

Analogous, possibly, proportional, yes.

 

N

[Gibbo]

Analogous, possibly, proportional, yes.

 

In this context, surely they mean exactly the same thing?

 

<runs off to Google "analogous", which obviously comes from "analogy", which is derived from the Greek word "analogia" meaning "proportion">

[Theo]

In this context, surely they mean exactly the same thing?

 

<runs off to Google "analogous", which obviously comes from "analogy", which is derived from the Greek word "analogia" meaning "proportion">

 

That is exactly why I put "possibly" . I had not given sufficient time to think it through thoroughly.

 

N

[lewisericeric]

Gibbo -

 

My charge voltage when the engine is on is 14.15-14.30. It ranges between those figures. Tonight it was on 14.25 at the highest when apparently the batts were at 100%. This was with lights and fridge on too.

 

I have seen the voltage hitting highs of 15 though on days when the solar panels and wind generator are working together?

[blodger]

Gibbo -

 

My charge voltage when the engine is on is 14.15-14.30. It ranges between those figures. Tonight it was on 14.25 at the highest when apparently the batts were at 100%. This was with lights and fridge on too.

 

I have seen the voltage hitting highs of 15 though on days when the solar panels and wind generator are working together?

I am surprised your charge voltage is as low as it is if it also has solar support at the same time. When I move my boat I see 14.6v. I am also surprised at the 15v highs since solar and wind controllers usually cap charging at 13.7v and I have to short out the controllers to di a bit of 14.8v charging. It is probably just me; I bought an 80 quid MPPT controller for the up to 30% charge improvement and I have taken it off as inferior to what I had previously!

[lewisericeric]

I usually run my engine after solar has finished and mainly for hot water for the night / next morning so wouldn't know what the solar and engine combined would be.

 

I bought an outback 80 amp controller and they're around 500 quid and have a solar array of nearly 700 watts so not sure if that's where the difference is between yours and mine?

 

Yesterday I was pulling in 47 amps at one point. Getting more now than during mid summer but apparently coooler, sunny days do result in more a,ps than 'hotter' days.