100AH lithium battery holds MORE power than 100AH lead acid??

[s/v Jedi]

Originally Posted by Simi 60

I ask because our Victron battery monitor, which reads a combination of 3 batteries, 24 cells combined is not as accurate as the actual Bluetooth monitor on the BMS that reads individual cells,

Each battery need it’s own battery monitor.

[s/v Jedi]

Let’s say you have a 12V LA battery bank and you want to seriously cycle it but don’t want the voltage drop mentioned here over and over.

Of course you can do this, you simply use a Victron 12/12 DC-DC converter like this one: https://www.victronenergy.com/upload...60-400W-EN.pdf

and you get a 13.2 or 13.8, whatever you want output voltage even when you run the battery all the way down to 9V or even 8V, yes probably even 7V. If that isn’t enough then you need a bigger battery.

I believe we will see this setup coming on more and more oem installations, ai’ve seen the first ones already.

[Putt-Putt]

Yoda.

You stated the dc-dc converter, but the link you attached is for the non-isolated dc-dc battery charger, which you can if you want to, set for a fixed voltage. Was that your intent?

[Simi 60]

Originally Posted by s/v Jedi

Each battery need it’s own battery monitor.

I had 8 AGM combined to make 880ah @ 24v and only 1 battery monitor

Now I have 24 X 3.5 v batteries, are you saying I need 24 battery monitors?

Easier to use the BMS Bluetooth monitor for each bank @ zero cost

[s/v Jedi]

Originally Posted by Putt-Putt

Yoda.

You stated the dc-dc converter, but the link you attached is for the non-isolated dc-dc battery charger, which you can if you want to, set for a fixed voltage. Was that your intent?

You don’t need isolation for this because the negative stays at the same potential. It is the positive which is changed from a varying battery positive oflets say between 9 and 14.5V to a fixed 13.2V

[s/v Jedi]

Originally Posted by Simi 60

I had 8 AGM combined to make 880ah @ 24v and only 1 battery monitor

Now I have 24 X 3.5 v batteries, are you saying I need 24 battery monitors?

Easier to use the BMS Bluetooth monitor for each bank @ zero cost

You are confusing cells vs batteries.

[Baronkrak]

Originally Posted by Simi 60

What makes you think it was undersized?
The AGM was 880ah @ 24 vs 840ah @ 24 for lifepo4

Your AGM maximum current is 44A (880Ah/20h).
For a start: Your 1.8kw hot water system requires 75A (1800W = 1800VA/24V).
Peukert Number Battery Life Calculator
May help you.

.

Originally Posted by Simi 60

Where are you getting the 80% used/20% left reading from?

Victron BMV-712 Smart, but read the disclaimer.

Originally Posted by Simi 60

I ask because our Victron battery monitor, which reads a combination of 3 batteries, 24 cells combined is not as accurate as the actual Bluetooth monitor on the BMS that reads individual cells,

My guess is that they do not read their voltage from the same point.

[Baronkrak]

Originally Posted by wholybee

….your cells are out of balance.

I get 330Ah from my 300Ah battery. I can take it all the way to 0%, and still not get a disconnect.

Of course the cells are out of balance.

Lucky you.

[noelex 77]

Originally Posted by Baronkrak

Your AGM maximum current is 44A (880Ah/20h).
For a start: Your 1.8kw hot water system requires 75A (1800W = 1800VA/24V)..

44A is not the maximum current. It is just the discharge current that will theoretically yield the 880Ahr rating.

At a higher discharge than 44A the capacity will be less than 880Ahrs. At a lower discharge than 44A the capacity of the battery will be higher than 880Ahrs. This often provides a slight bonus capacity for a marine lead acid bank, as most of the time the current draw will be less than the C20 rate. This means the real battery capacity will be higher than specified on the label.

As lead acid batteries do not need a BMS, the maximium current delivery of AGM batteries is very high.

[CaptainRivet]

Originally Posted by Chotu

And this is why it’s time for us to do the same. We are using antiquated lead thinking from back when there was only one battery chemistry.

It’s time for the AH to go as a measure of a battery’s capacity.

Yes true and i would to include a whole cycle in that means charge from empty to full and then discharge till empty. That also includes efficiency and losses into the picture.
You have to first put x WH into the battery till its fully charged and then you can take x WH out plus include the charge time as well.

That would look for a 1000WH lead:
1200WH in to get 1000WH, takes with 20A charge (C20) about 6.5h, then you discharge with 20A and get 850WH. Loss 350WH
For 1000WH Lifepo4 that would look like:
1010WH in to get 1000WH, takes with C20 charge about 5hand 5min, then discharge with 20A you get 990WH. LOSS 20wh.
Cranck up the current to 1C and it looks really bad for the lead...

[Baronkrak]

Originally Posted by noelex 77

44A is not the maximum current. It is just the discharge current that will theoretically yield the 880Ahr rating.

At a higher discharge than 44A the capacity will be less than 880Ahrs. At a lower discharge than 44A the capacity of the battery will be higher than 880Ahrs. This often provides a slight bonus capacity for a marine lead acid bank, as most of the time the current draw will be less than the C20 rate. This means the real battery capacity will be higher than specified on the label.

As lead acid batteries do not need a BMS, the maximium current delivery of AGM batteries is very high.

People should know that by now.

The fact he pull more than 75A give the following result.

Originally Posted by Simi 60

Easily proven for us.

We had 880ah @ 24v in AGM

[Baronkrak]

Originally Posted by Chotu

And this is why it’s time for us to do the same. We are using antiquated lead thinking from back when there was only one battery chemistry.

It’s time for the AH to go as a measure of a battery’s capacity.

And how would you account for MPPT behaviour?

[Putt-Putt]

Originally Posted by CaptainRivet

That would look for a 1000WH lead:
1200WH in to get 1000WH, takes with 20A charge (C20) about 6.5h, then you discharge with 20A and get 850WH. Loss 350WH
For 1000WH Lifepo4 that would look like:
1010WH in to get 1000WH, takes with C20 charge about 5hand 5min, then discharge with 20A you get 990WH. LOSS 20wh.
Cranck up the current to 1C and it looks really bad for the lead...

Last time I checked a 1000Wh battery at 12v would be an 83Ah battery that if you are charging/discharging it with a charge/load of 20A, would be a rate of C4.1, not a C20. Kind of hard on lead.
If you charge your 1000Wh LFP battery at a rate of 1/20 of the battery's capacity per hour (C20) how can it take just over 5 hours to complete a full charge?

Although high discharge rates are convenient when using your Dyson as it keeps the battery size and weight down, who here on their boat normally charges/discharges their LFP house bank at a C4 rate or a C1 rate? Imagine having to recharge you batteries completely every 1 to 4 hours.

[rwidman]

Lithium batteries are better in every way than flooded cell or AGM batteries except for their initial cost and their tendency to catch fire (something best avoided on a boat).

[Simi 60]

Originally Posted by rwidman

Lithium batteries are better in every way than flooded cell or AGM batteries except for their initial cost and their tendency to catch fire (something best avoided on a boat).

This has been beaten to death many times.

Lifepo4 batteries don't catch fire
And in many cases are cheaper now than FLA and AGM.

In Oz, our 840ah @ 24v Lifepo4 bank was about 50% cheaper than 840 usable ah of AGM