another set of electrical questions

[MtB]

3 hours ago, nicknorman said:

I have 450AH of battery capacity, MTB has only a pathetic 225AH. How does he cope? Oh!, could it be that he has a 24v system and thus his 225AH is worth exactly the same amount of energy as my 450AH!

 

Swerving slightly orf topic, I have noticed something curious. 

 

Although God turned my solar off a few weeks ago, now I have my lithiums in permanent use I notice the solar must be once again charging. I typically use about 30ah per day at 24v but after the last three days my BMV-702 is telling me I've used 28ah. How so?

 

Ok the solar is charging the lithiums unexpectedly but this has lead me to wonder about another effect. My BMV-702 is just configured 'out of the box', me being a beet feek (or lazy), so what with the default charge (in)efficiency and  Peukert factor programmed in by Victron, I gurss a few more AH have been delivered by the solar into the more efficient Li batts than Victron are reporting. 

 

I need to lie down after thinking about and writing that.... ?

 

 

[nicknorman]

6 hours ago, Mike the Boilerman said:

 

Swerving slightly orf topic, I have noticed something curious. 

 

Although God turned my solar off a few weeks ago, now I have my lithiums in permanent use I notice the solar must be once again charging. I typically use about 30ah per day at 24v but after the last three days my BMV-702 is telling me I've used 28ah. How so?

 

Ok the solar is charging the lithiums unexpectedly but this has lead me to wonder about another effect. My BMV-702 is just configured 'out of the box', me being a beet feek (or lazy), so what with the default charge (in)efficiency and  Peukert factor programmed in by Victron, I gurss a few more AH have been delivered by the solar into the more efficient Li batts than Victron are reporting. 

 

I need to lie down after thinking about and writing that.... ?

 

 

It is to some extent expected. The Lithiums output their AH at a higher voltage than your LAs, in other words 30AH of lithium power contains more energy than 30AH of LA power.

 

Many devices are “constant power” devices - fridges, phone chargers, TVs, LED lights with regulation, so if the voltage goes up the current/AH used decreases proportionally. Even pumps will use less charge to achieve the same thing at a higher voltage.

 

Yes there will also be some mis-reading due to the charge efficiency setting -should be set to unity for Li. Peukert however, isn’t used in calculating AH in/out nor SoC so not relevant. It only gets used for “time to run to flat at current discharge rate”.

 

These effects aren’t going to account for all the difference you mention, but some of it. It has also been quite sunny round our way this last couple of days.

[Richard10002]

On 18/11/2019 at 20:59, WotEver said:

Although it’s usually pretty accurate the Smartgauge shouldn’t be relied upon to tell you when your batteries are fully charged when you’re charging them - use the current and voltage as above. 

I think it is fair to say that any reading above 80% on the Smartgauge should be treated with suspicion. If you charge until the moment the Smartgauge shows 100%, you will almost certainly be undercharging your batteries, and will destroy them gradually, but over a relatively short period.

 

Your BMV700 should be fine in terms of monitoring your bank and establishing when it is fully charged.

 

 

[Tony Brooks]

12 hours ago, Richard10002 said:

Your BMV700 should be fine in terms of monitoring your bank and establishing when it is fully charged.

Not if you are using the % charged figure it wont. Only use Amps for that.

 

I suspect the % of charge figures are likely to be even more inaccurate with a battery technology that is not Lead Acid but which way wrong I have no idea.

 

Question to BVM users, can you alter the fiddle factor for charge efficiency?

[Sea Dog]

1 minute ago, Tony Brooks said:

Question to BVM users, can you alter the fiddle factor for charge efficiency?

Yes. Easily done in the menu.

[cuthound]

2 hours ago, Tony Brooks said:

Not if you are using the % charged figure it wont. Only use Amps for that.

 

I suspect the % of charge figures are likely to be even more inaccurate with a battery technology that is not Lead Acid but which way wrong I have no idea.

 

Question to BVM users, can you alter the fiddle factor for charge efficiency?

 

You also need to adjust the battery capacity to as close to actual (sulphated in the case of LA's) capacity and set change tail current setting from 4% (default) to 2% or less, and regularly reset the BMV when you know the battery is fully charged if you want the BMV SoC meter to read anything like accurately.