Battery problem?

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Originally Posted by Pedro_The_Swift

Anyone care to workout the voltage drop on a 6metre cable run of 13v at 20A using 6awg?
is 0.45v close?

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Hi Pedro, the voltage drop is really an irrelevance in a battery charging circuit.

The fact you are using such thick cable means you will get a good charge at the batteries.

While the batteries are low, the voltage at the regulator will also be low because the battery draw current will pull the regulator voltage down.

Yes you could have as much as 0.45 while the batteries are charging, but the voltage drop is caused because the batteries are being charged at 20 amps and are pulling 20 amps, and this is regardless of the voltage.

As the batteries state of charge rises towards a fully charged level, the batteries themselves, will pull less current and this will mean the voltage drop between the regulator and the battery terminals will get smaller.

Again, because you have used such thick cable, you should have no problems fully charging your batteries, with the only limiting factor in your case, is how much time your have to charge the batteries.

Quote:

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Originally Posted by Pedro_The_Swift

Anyone care to workout the voltage drop on a 6metre cable run of 13v at 20A using 6awg?
is 0.45v close?

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Following on from Drivesafe's advice, for your "academic" interest however ,

check out Voltage Drop Calculator
Plugging in your Voltage and Current data, the calculated Vdrop is 0.312... which may well be different in "real world" for different resistivity of multi-strand wire and other factors... This table takes into account that you need to actually calculate the drop over 2 x 6m =12m... (for the return path)

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Originally Posted by PhilipA

I posted the battery charge percentages a few days ago. These apply to virtually all LiFePO4 batteries.
Resting charge should be 13.6-8 for a fully charged battery.

Regards PhilipA

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Originally Posted by drivesafe

I have a string of different lithium batteries, and I have never seen lithium batteries with a settled voltage that high. Maybe straight after a charger is removed, but normal settled voltage is 13.1v to 13.3v.

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I installed my 2 x 50Ah lithium batteries into the (Kimberley) camper trailer 8 months ago. I have always kept the Victron IP65 charger connected to them while the camper is not in use. The AGM's they replaced had a BM2 monitor attached so I attached that to the lithiums when I installed them.

I had not previously checked the settled voltage before. The Victron told me it was at Storage at 13.84V and the BM2 at 13.79 when I disconnected the power to the charger. That 0.05V discrepancy has been pretty consistent over the last 8 months since installation.

12 hours later the BM2 was reading 13.74.

24 hours later the BM2 was reading 13.69.

36 hours later (this morning) the BM2 is reading 13.65.

I know that the BM2 is not necessarily the most exact measurement tool in this instance but it certainly appears the voltage of my batteries is not dropping off a cliff even if the voltage is dropping slowly as they settle.

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Originally Posted by Narangga

I installed my 2 x 50Ah lithium batteries into the (Kimberley) camper trailer 8 months ago. I have always kept the Victron IP65 charger connected to them while the camper is not in use. The AGM's they replaced had a BM2 monitor attached so I attached that to the lithiums when I installed them.

I had not previously checked the settled voltage before. The Victron told me it was at Storage at 13.84V and the BM2 at 13.79 when I disconnected the power to the charger. That 0.05V discrepancy has been pretty consistent over the last 8 months since installation.

12 hours later the BM2 was reading 13.74.

24 hours later the BM2 was reading 13.69.

36 hours later (this morning) the BM2 is reading 13.65.

I know that the BM2 is not necessarily the most exact measurement tool in this instance but it certainly appears the voltage of my batteries is not dropping off a cliff even if the voltage is dropping slowly as they settle.

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OK, this is very much a "newbie" question. Does the controller/charger ( any, not just yours ) display the actual battery voltage, ie the potential difference between +ve and -ve posts, or does it display what the chip in the battery says it is?

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Originally Posted by Narangga

I installed my 2 x 50Ah lithium batteries into the (Kimberley) camper trailer 8 months ago. I have always kept the Victron IP65 charger connected to them while the camper is not in use. The AGM's they replaced had a BM2 monitor attached so I attached that to the lithiums when I installed them.

I had not previously checked the settled voltage before. The Victron told me it was at Storage at 13.84V and the BM2 at 13.79 when I disconnected the power to the charger. That 0.05V discrepancy has been pretty consistent over the last 8 months since installation.

12 hours later the BM2 was reading 13.74.

24 hours later the BM2 was reading 13.69.

36 hours later (this morning) the BM2 is reading 13.65.

I know that the BM2 is not necessarily the most exact measurement tool in this instance but it certainly appears the voltage of my batteries is not dropping off a cliff even if the voltage is dropping slowly as they settle.

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Hi Dale and sorry, I missed replying to your question.

I don't take to much notice of the "settled" voltage of any battery after they have been charged, regardless of what is used to charge them.

All batteries once fully charged properly, will have a surface voltage.

While lead acid batteries usually loose this surface charge a few hours after being charged, I have noticed that lithium batteries can hold a surface charge for many days.

In both cases, with either lead acid batteries and lithium batteries, applying a small load, will very quickly remove the surface charge and you will get a more accurate settlement voltage reading.

This is also why I have always recommended people ignore "OPEN CIRCUT" type voltage reading and make sure you have at least a small load applied to the battery for a short period of time before taking a voltage reading with any lead acid battery, while that load is still applied.

Back to the lithium voltage readings. I have two 100Ah lithium batteries, of the same brand and age and while one was last charged ( but not used ) 3 month ago, the other was charged and then removed from in my VW Tiguan two weeks ago, and both are sitting at 13.34, with no load applied.

Later on today, I will apply a small load to each of them and see what voltage they have then.

BTW, I find BM2 Bluetooth battery monitors have very accurate voltage readings.

I have a 100AH VoltX cheapy in my Caravan and after 4 months of non use and not charged it reads 13.27 volts through my simple amp, watt etc in line monitor. I have a master switch between the monitor and battery.

The battery has been connected when I wanted to test newly installed lights etc from time to time.

I note that after driving and charging through my Renolgy 20amp DC/DC charger it starts at about 13.8 resting then quickly drops to 13.6 then to 13.3 after say one night use for interior lighting and pump.(about 2-4AH).

I charge at max 14.4 for safety sake as the Renolgy has max volt options. The battery charges quite quickly doing that.
Regards PhilipA

Finally got onto a Victron rep that had some common sense, ( the last wanted me to rewire the van and relocate the batts...) aparently Victron make a "Smart Battery Sense" that when attached to the batts talks to the controller via bluetooth and boosts the output to cover voltage drop..
Problem Solved.
Now I just to find one in WA..

post deleted -applied to 24V or 48 V only..."mea culpa"[bighmmm]

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Originally Posted by Hoges

post deleted -applied to 24V or 48 V only..."mea culpa"[bighmmm]

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Dimittuntur tibi

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Originally Posted by Tins

Dimittuntur tibi

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[bigrolf]