Visit our Popular Forums

Happ · 06-02-2023, 06:29

Quote:

Originally Posted by Fuss

You're sailing along not a care in the world and behind the scenes your Lifepo4 just hit 80% depth of Discharge.

How were you informed?

What procedures now took place?
Were any of these procedures automated?

I am just interested to know how others are handling this....

or is it as simple as, an alarm down below went off and I started the motor and had a bit of a look at the battery monitor for the next few hours and once the capacity was looking better, I switch the motor off and went back to the sailing.

You attach a battery monitor like a Victron. Set it up for the batteries you have.

Sailing Hanse37 · 06-02-2023, 06:35

Quote:

Originally Posted by Simi 60

And they aren't accurate anyway.
At least our victron isn't.
It always reads quite a bit different to the JBD BMS Bluetooth app

Ou Victron battery monitor is within a few % showing the same state of charge as the bluetooyh BMS.

AndyEss · 06-02-2023, 14:12

Quote:

Originally Posted by s/v Jedi

Then there is a problem with the shunt installation. All current to/from the battery must go through the shunt.

Also, you can download the VictronConnect app and enjoy all readings and settings from the comfort of your bed in the morning as well

Just for others reading this: accuracy of the Victron BMV is much higher than for most BMS systems, plus it gives a total overview of the whole bank of batteries. It is accurate to 0.01V, 0.01A, 0.1Ah and 0.1% SOC.

I’m not on my boat right now, but what you quoted as “accuracy” is resolution of the digital readouts, not even close to “accuracy”

The SOC for one, depends on accumulation of data of battery use, measured across the shunt. There is no temperature compensation element (AFAIK) across the resistances measured across the shunt, which get converted to both voltages and amperages using Ohm’s Law.
The resistance of any metal is temperature dependent, and not infrequently non-linear across the temperatures a shunt may experience in conditions of normal use.
From my observations on my Victron BMV, I would be surprised if it had 5% accuracy in use.
No big deal as long as you have a good solar array capacity relative to your battery bank size and your usual electrical usage.

wgerstmyer · 06-02-2023, 14:33

Hi fellow Mainer Mariner,
Link to a good build your own instruction? Thanks, Will

Icarus · 06-02-2023, 22:22

Quote:

Originally Posted by Fuss

You're sailing along not a care in the world and behind the scenes your Lifepo4 just hit 80% depth of Discharge.

How were you informed?

What procedures now took place?
Were any of these procedures automated?

I am just interested to know how others are handling this....

or is it as simple as, an alarm down below went off and I started the motor and had a bit of a look at the battery monitor for the next few hours and once the capacity was looking better, I switch the motor off and went back to the sailing.

When the lights go dim?
Battery alarm comes on?

I guess the 'procedure' is to charge the batteries...pretty obvious I thought.

Pretty much applies to all batteries.
Cheers

Carlisle Spirit · 06-02-2023, 22:50

Quote:

Originally Posted by SailingHarmonie

The question as phrased does not compute. The idea that my batteries could drop to a SOC that was so low it triggered the alarm without me being fully aware it was going to happen is just foreign to me. Kind of like being "surprised" by a low fuel light coming on when motoring down the highway. I am pretty tuned in to our batteries, at any point in time--without looking at the gauges--I could probably tell you the SOC within 5%.

But... more in the spirit of the OP's question: When my batteries get down to the lowest "normal" state of charge, the generator starts automatically, and runs until the charge acceptance drops to the point where I know they are about 93% charged. This is not a lithium bank, but my logic would be very similar if they were (although the settings might well be different).

All this is controlled by a Victron Cerbo. The generator is a WhisperPower 3.5kW DC genset that runs through its autostart cycle when the Cerbo closes a relay, and continues to run until that relay opens.

Here is the logic: From 0600 to 1800 the generator comes on if the SOC drops below 65%. In our world this effectively means the generator starts every other day at 0600. Outside those hours, the generator will start if the SOC drops below 55%, I can not remember the last time this happened.

The generator runs until the charge acceptance drops to a level I have found equates with 93% SOC. I use charge acceptance rate, because it is a very accurate indication of SOC for these AGM style batteries. From 93%, a normal solar day takes me to 100% by the end of the day.

This system has worked well for us for almost 3 years. When these batteries die, eventually, I'll probably go with Li, but that is a long way away, and its way too early to predict what will be state of the art at that point.

Your setup sounds interesting - using the Victron Cerbos to start the generator

Difficult to set up ?

**s/v Jedi** · 07-02-2023, 00:18

Quote:

Originally Posted by AndyEss

I’m not on my boat right now, but what you quoted as “accuracy” is resolution of the digital readouts, not even close to “accuracy”

The SOC for one, depends on accumulation of data of battery use, measured across the shunt. There is no temperature compensation element (AFAIK) across the resistances measured across the shunt, which get converted to both voltages and amperages using Ohm’s Law.
The resistance of any metal is temperature dependent, and not infrequently non-linear across the temperatures a shunt may experience in conditions of normal use.
From my observations on my Victron BMV, I would be surprised if it had 5% accuracy in use.
No big deal as long as you have a good solar array capacity relative to your battery bank size and your usual electrical usage.

You are correct about resolution vs accuracy but your estimation of accuracy is way off. Actual accuracy is 0.4% for current measurement and 0.3% for voltage measurement. This is data from the spec sheet.

Simi 60 · 07-02-2023, 03:03

Quote:

Originally Posted by Sailing Hanse37

Ou Victron battery monitor is within a few % showing the same state of charge as the bluetooyh BMS.

That's nice

I just reconfigured ours for the umpteenth time over the last few days and it's gone a whole new level of retardation.

Now, we have the solar mppt and the BMS saying there is around 50 amps coming in and the victron showing rapidly changing amps , sometimes in the negative.
Also shows batts at 100% when we are at around 60%

Fuss · 07-02-2023, 03:14

I originally asked this question as I was thinking of getting a BMV 712 and using it for alternator HV Cutoff and possibly also having some alternator automation when the batteries get low. But now i'm thinking of just using a manual switch so I can switch the alternators on and off as I feel like it. I mean all other charging sources have switches so why not the alternators. Its a long period between fully charged and empty so I guess I always know roughly the state of charge and if I was motoring a long way and the batteries are full, then I would just switch off the alternators. Somehow I feel happier with this than having it automated.

**s/v Jedi** · 07-02-2023, 04:36

Quote:

Originally Posted by Fuss

I originally asked this question as I was thinking of getting a BMV 712 and using it for alternator HV Cutoff and possibly also having some alternator automation when the batteries get low. But now i'm thinking of just using a manual switch so I can switch the alternators on and off as I feel like it. I mean all other charging sources have switches so why not the alternators. Its a long period between fully charged and empty so I guess I always know roughly the state of charge and if I was motoring a long way and the batteries are full, then I would just switch off the alternators. Somehow I feel happier with this than having it automated.

A switch is fine but you still need a way to save the rectifier diodes when the BMS switches offline. If your BMS can’t do it then a dc-dc converter is the way to circumvent this.

**s/v Jedi** · 07-02-2023, 04:36

Quote:

Originally Posted by Simi 60

That's nice

I just reconfigured ours for the umpteenth time over the last few days and it's gone a whole new level of retardation.

Now, we have the solar mppt and the BMS saying there is around 50 amps coming in and the victron showing rapidly changing amps , sometimes in the negative.
Also shows batts at 100% when we are at around 60%

Time to hire a pro

Worst case your BMV has expired. You need to get this fixed.

Fuss · 07-02-2023, 08:22

Quote:

Originally Posted by s/v Jedi

A switch is fine but you still need a way to save the rectifier diodes when the BMS switches offline. If your BMS can’t do it then a dc-dc converter is the way to circumvent this.

I have two mini 12v, 1.3ah lead batteries in series that are connected to the 24v house bank using a switch. They are connected when I switch on the motor I was thinking of using this same switch to switch on/off the 2 alternator requlators. So when the alternators are switched on, the mini batteries are also connected to the house bank.

**s/v Jedi** · 07-02-2023, 08:25

Quote:

Originally Posted by Fuss

I have two mini 12v, 1.3ah lead batteries in series that are connected to the 24v house bank using a switch. They are connected when I switch on the motor I was thinking of using this same switch to switch on/off the 2 alternator requlators. So when the alternators are switched on, the mini batteries are also connected to the house bank.

Doesn’t sound adequate. Unless you confirm protection by testing, I suggest a 100Ah start battery on the alternator, then a smart dc-dc charger from there to the house battery.

Fuss · 07-02-2023, 08:42

Quote:

Originally Posted by s/v Jedi

Doesn’t sound adequate. Unless you confirm protection by testing, I suggest a 100Ah start battery on the alternator, then a smart dc-dc charger from there to the house battery.

I didn't test it. It would be an interesting experiment though. I just don't feel like having to replace all my diodes for the sake of a test.
The start batteries only start so they are charged by a 24v - 12v charger from the house bank. I have 2 x 24v house batteries so there is a little safety there of a total disconnect without me knowing.