Opinions on new LiFePO4 housebank install

[Britishsea]

Originally Posted by smac999

the victron dc to dc will drop the amps to maintain the voltage on the start battery.

IE if you set the voltage cut off to 13.2v which I think is the default for smart alt. the start battery will not go under that. so if drawing 30a is more then the alt can put out, causing the start battery to drop below 13.2v the charger will claw back. and maybe only output 20a.

this is really handy when you have a bunch of them. I put 5 on one boat. 90a from one engine and 60a from the other. at idle they will just claw back the current.

unlike the mastervolt dc to dc which will just cycle on and off at full amps if the alt can't keep up.

That's interesting. Did not know they behaved that way. Mine were off my LFP bank, so really no voltage drop there. As a result, I had it set up to be triggered by an ignition circuit to the remote input and not using the voltage the Orion's voltage sensing function.

[Britishsea]

I was looking into this further and found this Victron summary on the "Volt Sense" function for the Orion TR DC-DC and how it manages an alternator that can't keep up with its output.

https://www.victronenergy.com/upload...Charger-EN.pdf

[jlodolce]

What batteries have you chosen?

[goboatingnow]

A DC to dc converter is just a switched mode power supply , a jelly bean circuit. If it’s set to a constant voltage then it will “ attempt “ to do that within the ability of its power source.

If the load demands more then the source can supply , the dc dc can only reduce its output voltage until its VxI product equals the available input power at that point , hence its output voltage will fall until the current x volts is consistent

It cannot claw anything back , other then follow ohms law

So say the power source is good for 100W , and the load is 1 ohm , then if the regulated load voltage desired was 10 v. Then all is well , but let’s say the load wanted more power so it’s effective resistance haved to 0.5 ohm the dc dc converter would have to let its output voltage fall to 5v to satisfy ohms law. The dc dc cannot “ hold” the output voltage up to 10v or anything higher then 5v at that point

[team karst]

Jelly bean circuit. [emoji848]

[goboatingnow]

Originally Posted by team karst

Jelly bean circuit. [emoji848]

Jelly beans in electronics are very common things , “ jelly bean components “ , “jelly bean circuits” etc

The fundamental dc dc building blocks are very common circuits. Dc dc gets used all over electronics for all sorts of activities.

[team karst]

New to me. I will use that on my next design reviews!

In fact, a couple days ago, i suggested a murata dcto dc and not a roll ur own circuit.

[goboatingnow]

Originally Posted by smac999

the victron dc to dc will drop the amps to maintain the voltage on the start battery.

IE if you set the voltage cut off to 13.2v which I think is the default for smart alt. the start battery will not go under that. so if drawing 30a is more then the alt can put out, causing the start battery to drop below 13.2v the charger will claw back. and maybe only output 20a.

this is really handy when you have a bunch of them. I put 5 on one boat. 90a from one engine and 60a from the other. at idle they will just claw back the current.

unlike the mastervolt dc to dc which will just cycle on and off at full amps if the alt can't keep up.

The victron dc dc system doesn’t do that , I have one fitted

What it does have is a engine running detection , essentially it differentiates between a battery voltage and the alternator voltage , by unloading the charger for 10 secs. This is to allow differentiation between a loaded battery with alternator and one unloaded with alternator

If the measured voltage with the DC dc unloaded is above a fixed point it will re start charging , if it’s below the shutdown it will pause charging

It does not “ claw back current , that’s impossible. If the charging load forces the input voltage below the shutdown figure it will shut off charging

It is however a buck and boost charger , so it can maintain the output power for any combination of input voltage and current this is why it’s senses engine on , to ensure it doesn’t drain the source battery. It can in theory work down to 8v , so it could without such controls utterly discharge the source

It will continue to draw as much power as the load needs until it pulls the source below the shutdown threshold.

The engine running detection isn’t foolproof , especially if other big consumers are online.

[Captain Bill]

Originally Posted by jlodolce

What batteries have you chosen?

I decided to buy Chins 100ah. They are very inexpensive and only time will tell if this was a stupid decision. I got the boat wiring rearranged and the batteries installed Thursday afternoon. When they arrived all three were sitting at 13.17 volts. I opted for the dumb BMS, which again might have been the dumb decision. The main advantage of the smart BMS is the low temperature charging protection. Since I live in SW Florida and my batteries are below the waterline I sincerely hope I never see temps below 0 C. My biggest concern is that the low end BMSs will not be up to the task long term. It was one of the reasons I opted for 3 100ah batteries instead of 1 300ah battery.



Once I got them installed I charged them to 100%. It took about 1.7 hours with a 100 amp charger and about 15amps from the solar. I disconnected them from the 100a charger. Overnight they dropped to 3.28Vwhich if I'm reading the chart correctly is about 87-88%. Friday morning was broken clouds and they were still back to 100% by 10:50am.

This morning it was clear and the charge was already at 100% when I looked at 10:30. My static house loads run about .7 amps. My fridge is new and draw about 6 amps when running but due to winter temps down here the duty cycle is pretty low. From Sunset yesterday to 5:00 this afternoon the Solar controller had put out only 59.5ah. We'll use a lot more when we get off the dock again, but everything is looking good so far.

[Hermia II]

Here's what I did (hope my .pdf circuit diagram is visible below). Grateful for comments since I haven't hit the start button yet :-)

[fxykty]

Originally Posted by Captain Bill

I decided to buy Chins 100ah. They are very inexpensive and only time will tell if this was a stupid decision. I got the boat wiring rearranged and the batteries installed Thursday afternoon. When they arrived all three were sitting at 13.17 volts. I opted for the dumb BMS, which again might have been the dumb decision. The main advantage of the smart BMS is the low temperature charging protection. Since I live in SW Florida and my batteries are below the waterline I sincerely hope I never see temps below 0 C. My biggest concern is that the low end BMSs will not be up to the task long term. It was one of the reasons I opted for 3 100ah batteries instead of 1 300ah battery.



Once I got them installed I charged them to 100%. It took about 1.7 hours with a 100 amp charger and about 15amps from the solar. I disconnected them from the 100a charger. Overnight they dropped to 3.28Vwhich if I'm reading the chart correctly is about 87-88%. Friday morning was broken clouds and they were still back to 100% by 10:50am.

This morning it was clear and the charge was already at 100% when I looked at 10:30. My static house loads run about .7 amps. My fridge is new and draw about 6 amps when running but due to winter temps down here the duty cycle is pretty low. From Sunset yesterday to 5:00 this afternoon the Solar controller had put out only 59.5ah. We'll use a lot more when we get off the dock again, but everything is looking good so far.

You do know that regular charging to 100% state of charge is not necessary nor good for LFP batteries? The optimum operating range is 30-70% SOC. Most people give up a few thousand cycles and use 20-80% SOC. Once a month or so charge to 100% SOC (based on residual current at a certain voltage) to reset the BMS, but otherwise stay below 80%!

Your cheap BMS may not be able to stop charging at a certain SOC and/or voltage, so you need to manage that manually. Can you configure the solar controller to stop charging at a certain voltage?

[Captain Bill]

Originally Posted by fxykty

You do know that regular charging to 100% state of charge is not necessary nor good for LFP batteries? The optimum operating range is 30-70% SOC. Most people give up a few thousand cycles and use 20-80% SOC. Once a month or so charge to 100% SOC (based on residual current at a certain voltage) to reset the BMS, but otherwise stay below 80%!

Your cheap BMS may not be able to stop charging at a certain SOC and/or voltage, so you need to manage that manually. Can you configure the solar controller to stop charging at a certain voltage?

I've heard this many times, but I don't have a way of stopping the charge at 80% and still putting any electrons in the battery. If I set the absorption voltage on my charger to 13.2 it would take a couple of days just to replace the power I use overnight. The amps were not high enough with the small delta V to charge the battery back to 80% in a reasonable amount of time. I'm certainly not going to sit and watch my voltmeter until I pull the plug so to speak. The purpose of the boat is to go cruising, not to watch a voltmeter. My understanding is that it's holding them at 100% that is the biggest problem, at least in comparison to letting them touch 100%. It's pretty clear to me that my only real choice here is to charge them to 100% then reduce the float voltage on my solar charger to around 13.25 or 13.3. I haven't decided which to use yet. Refrigeration and other loads will draw them down to the float voltage reasonably quickly and then the solar can carry the house loads until the sun gets too low. I understand that this is not ideal, but then again I paid less for these batteries than I did for the AGMs that lasted only 3.5 years. If these only last 2000 cycles I still only paid about half of what I would have for the AGMs. These are rated at >2000 cycles at 0-100%. If I can stretch the to 3000 cycles it's still a deal.

[Baronkrak]

Originally Posted by Hermia II

Here's what I did (hope my .pdf circuit diagram is visible below). Grateful for comments since I haven't hit the start button yet :-)

Nice drawing but for a start.
If the Cyrix opens you have a total black out.
The battery configuration lack protection.
You need to differentiate between switches and circuit breakers.

[Hermia II]

Originally Posted by Baronkrak

Nice drawing but for a start.
If the Cyrix opens you have a total black out.
The battery configuration lack protection.
You need to differentiate between switches and circuit breakers.

True, that's the idea behind the Cyrix. The generator should start automatically at 15% SOC, if not an alarm will sound 30 sec before shut down. The engine and the generator are started by other lead/acid batteries and can be started if Cyrix is open.
Each parallel 24v battery pair is fused by a 150A fuse according to Victron recommendations.
The meaning of the third remark is not clear to me.

[team karst]

automatic start machinery is quite edgy. In any space, much less in a ER.