Backup Lithium Solution

[goeasy123]

What's the best way to configure/modify a conventional 12v lead acid based system to 'plug in' something like an Ecoflow or Anker 767 LiFePO4 powerstation for emergency back up purposes.

I do not want LifPO4 in the permanent system, hybrid or otherwise for various good reasons. What subsystem do I need to connect a powerstation to the boats 12vdc bus while avoiding large potential differences and how do I get an adequate (i.e. sufficient current) 12vdc supply out of the powerstation?

 

[PaulRainbow]

Have you seen the price of an Anker 767 ?

Do you not have an engine battery ?

 

[Kelpie]

Curious what your good reasons are.

If you just run off LFP instead of lead acid, then there's no potential difference. I would simply connect the LFP to the negative of your existing setup, then pull the positive and put it on the LFP. Assuming it's just a backup emergency power supply then it might not be worth the hassle of doing anything more complicated.

On my boat, I ran a common negative, then the positive on each type of battery has an isolator. In theory you could run them in parallel by turning them both on, but I only have one key and you have to shut one bank off to remove the key, and then use that to turn on the other. Of course everything turns off for a few seconds during the swap but it's not a big deal. This also means that if the LFP goes down for any reason, it's just a few seconds to power up again from the lead acid.

 

[PaulRainbow]

Curious what your good reasons are.

If you just run off LFP instead of lead acid, then there's no potential difference. I would simply connect the LFP to the negative of your existing setup, then pull the positive and put it on the LFP. Assuming it's just a backup emergency power supply then it might not be worth the hassle of doing anything more complicated.

On my boat, I ran a common negative, then the positive on each type of battery has an isolator. In theory you could run them in parallel by turning them both on, but I only have one key and you have to shut one bank off to remove the key, and then use that to turn on the other. Of course everything turns off for a few seconds during the swap but it's not a big deal. This also means that if the LFP goes down for any reason, it's just a few seconds to power up again from the lead acid.

So, when you switch to the Lithium, what measure do you have in place to manage the battery and charging systems ?

 

[Kelpie]

So, when you switch to the Lithium, what measure do you have in place to manage the battery and charging systems ?

The lithium has a BMS and is charged by the MPPTs only.
The lead acid is charged by the alternator and a smaller set of solar panels.

 

[geem]

Curious what your good reasons are.

If you just run off LFP instead of lead acid, then there's no potential difference. I would simply connect the LFP to the negative of your existing setup, then pull the positive and put it on the LFP. Assuming it's just a backup emergency power supply then it might not be worth the hassle of doing anything more complicated.

On my boat, I ran a common negative, then the positive on each type of battery has an isolator. In theory you could run them in parallel by turning them both on, but I only have one key and you have to shut one bank off to remove the key, and then use that to turn on the other. Of course everything turns off for a few seconds during the swap but it's not a big deal. This also means that if the LFP goes down for any reason, it's just a few seconds to power up again from the lead acid.

Wouldn't it be more convenient with a 1,2, both switch to swap the batteries over? There isn't any downside to joining the banks momentarily from what I have read or am I wrong?
I have this issue to resolve when I add a lithium bank.

 

[stephen_h]

Have a look at these BOS LE200

Just add to your present system.

 

[Kelpie]

Wouldn't it be more convenient with a 1,2, both switch to swap the batteries over? There isn't any downside to joining the banks momentarily from what I have read or am I wrong?
I have this issue to resolve when I add a lithium bank.

Possibly. It was easier and cheaper to do it this way. I don't mind losing power for a couple of seconds. And I'm not entirely convinced that putting two different voltages of battery in parallel won't risk blowing a fuse or something.

I should add that this cross over only applies to the navigation systems. The fridge etc remain on the lithium.

 

[goeasy123]

OP Here. Some reasons:

- I want the a powerstation to take off the boat for other purposes.
- There's nothing wrong with my existing LA system and I don't need to change my usage profile.
- I sail in remote locations and on long passages and do not want the risk of binary failure inherent with LI vs LA.
- Limited insurance options.

BTW... when is say 'potential difference' in my original I mean the voltage PD which could be large. So NO 1,2, Both switch.

 

[Poey50]

Have a look at these BOS LE200

Just add to your present system.

£450 for 25.6 ah of extra capacity? Wow. The raw cells inside the plastic covering would cost 1/10 of that on the open market.

I can quite understand though that these could increase your lead acid longevity to up to 10 years. The reason for this is that the LFP will keep the lead acid on float the entire time. It will be the LFP that will be discharged and charged preferentially. So essentially the lead acid is there as an emergency back-up. If you keep a lead acid fully charged then - yes - a long life is to be expected. However if you decide to discharge deeply into your lead acid then you are likely to struggle to get it back to full because of the preferential charging of the LFP as said, and the long charging tail to get lead acid to 100% to avoid sulfation. So depending on usage these very expensive add-ons may give you a long lead acid life or an exceptionally short one.

 

[goeasy123]

Have a look at these BOS LE200

Just add to your present system.

This won't work for me. I want something to stand in for the LA if and when it goes down. The BOS LE needs a sound LA system to work.

 

[Kelpie]

That is more than I spent on my 271Ah battery. Even my little portable 60Ah battery was under £300.

What exactly are you wanting to power off this lithium supply?

 

[goeasy123]

That is more than I spent on my 271Ah battery. Even my little portable 60Ah battery was under £300.

What exactly are you wanting to power off this lithium supply?

As I say... the BOS LE won't work. I don't want one at any price.

I want a powerstation so that I can take it off the boat to run a PA and instrument amps far a band.... amongst other things.

 

[geem]

BTW... when is say 'potential difference' in my original I mean the voltage PD which could be large. So NO 1,2, Both switch.

I am not sure the 1,2 both switch in that scenario is an issue assuming the switch is suitably rated for the potential flow of current. Some people link their lead and lithium banks when running an inverter simply because a BMS shutdown whilst operating an inverter will likely blow the inverter to bits. Of course a very depleted lead battery would draw a lot of amps but the inherent high resistance of the lead battery would help to reduce this.

 

[Poey50]

What's the best way to configure/modify a conventional 12v lead acid based system to 'plug in' something like an Ecoflow or Anker 767 LiFePO4 powerstation for emergency back up purposes.

I'm struggling with the premise that LFP should act as an emergency back-up. LFP has several modes of rapid failure whereas lead acid rarely fails suddenly so the usual way round is that lead acid is the fall back chemistry.

 

[Kelpie]

As I say... the BOS LE won't work. I don't want one at any price.

I want a powerstation so that I can take it off the boat to run a PA and instrument amps far a band.... amongst other things.

Does this power station provide a 240v supply? In which case you could use something like a Victorian IP22 charger set to PSU mode to supply 12v for the boat. But it's an expensive and inefficient method.

 

[Kelpie]

a BMS shutdown whilst operating an inverter will likely blow the inverter to bits.

Slight thread drift but I wasn't aware that this was common knowledge. I killed my original inverter when the BMS tripped, I thought I had just been very unlucky.
How is a BMS shutdown any different from just turning off the power?

 

[geem]

Slight thread drift but I wasn't aware that this was common knowledge. I killed my original inverter when the BMS tripped, I thought I had just been very unlucky.
How is a BMS shutdown any different from just turning off the power?

I killed an old inverter as well switching off at the battery instead of removing the load first. It was a cheap jobby but even so I had to but a new one. Apparently its the Capacitors in the inverter that don't like it.

 

[vas]

don't think my victron multi ii cares, have done it a few times, no issues

 

[Kelpie]

My ex-inverter was from Epever, who I didn't think were too bad. But an over-current trip killed it. I was only trying to draw 1500w and it was rated at 3kw.
Replaced with a Victron, which cost the same as the rest of the system put together