One for the electrical experts

[dune16]

Hi,

I've recently upgraded my domestic bank to lifepo4. My 2 start batteries remain as agm's charged by a separate Cristec charger and the alternators. Previously when I was all agm I used to leave the boat plugged into shorepower over winter when I wasn't there for about 3 months. The issue I now have is the lifepo's don't really want to be sat at 100% charge with little draw on them. In an ideal world I would disconnect shorepower and let the solar deal with the domestic bank. But... this would mean the 2 x agm's sitting there not being charged for 3 months and I believe this could damage them. I can ask the marina to plug the shorepower in every few weeks for a day or so to charge the agm's bit is there a better solution (ideally simple)? I was thinking to somehow remotely be able to switch shorepower on and off? Another possible solution is a couple of sterling battery maintainers from the lifepo's to the 2 agm's?

Thanks in advance.

 

[Sea Change]

Can you disconnect the LFPs but leave everything else connected?
You might even be able to get in to the BMS via Bluetooth and disable charging, saves any physical changes.

 

[dune16]

Can you disconnect the LFPs but leave everything else connected?
You might even be able to get in to the BMS via Bluetooth and disable charging, saves any physical changes.

I should have mentioned, I like to leave the domestic bank on just to power wifi router and a couple of cctv cameras so turning the lfp's off not really an option although I can turn the charge voltage down so they don't sit at 100% soc.

 

[Sea Change]

I should have mentioned, I like to leave the domestic bank on just to power wifi router and a couple of cctv cameras so turning the lfp's off not really an option although I can turn the charge voltage down so they don't sit at 100% soc.

Yes I suppose you could adjust the HVD setting, if the BMS gives you that option.

 

[geem]

I should have mentioned, I like to leave the domestic bank on just to power wifi router and a couple of cctv cameras so turning the lfp's off not really an option although I can turn the charge voltage down so they don't sit at 100% soc.

Install a small victron dc/dc charger to keep the engine batteries on float, powered by the lithium. Imdo this for my engines batteries and the generator battery

 

[dune16]

Install a small victron dc/dc charger to keep the engine batteries on float, powered by the lithium. Imdo this for my engines batteries and the generator battery

I assume it's OK to connect a single charger (something like the Victron Orion TR) to 2 seperate batteries?

 

[geem]

I assume it's OK to connect a single charger (something like the Victron Orion TR) to 2 seperate batteries?

Do you mean to series or two parallel batteries? My engine is 24v so I have a pair of 12v 100Ah batteries wired in series to give 24v for starting. I have a dc/dc 24/24v charger that keep the pair of series wired batteries charged and on float.

 

[dune16]

Do you mean to series or two parallel batteries? My engine is 24v so I have a pair of 12v 100Ah batteries wired in series to give 24v for starting. I have a dc/dc 24/24v charger that keep the pair of series wired batteries charged and on float.

2 Seperate 12v agm's, 1 for each engine

 

[PaulRainbow]

2 Seperate 12v agm's, 1 for each engine

If you connect a single DC-DC charger to both batteries they will be in parallel, no longer separate. You could connect a DC/DC charger to one battery and fit a VSR between them.

 

[dune16]

If you connect a single DC-DC charger to both batteries they will be in parallel, no longer separate. You could connect a DC/DC charger to one battery and fit a VSR between them.

I already have a couple of argofet isolators to deal with charging from alternators and shorepower. I'm just struggling to picture where the vsr would fit in. Diagram attached. Thanks.

 

[PaulRainbow]

I already have a couple of argofet isolators to deal with charging from alternators and shorepower. I'm just struggling to picture where the vsr would fit in. Diagram attached. Thanks.

It would connect between the positive terminal of each engine battery.

You can make those connections at the batteries, the engine battery isolators, the engine terminals of the Argofets or the engine terminals of the three outlet mains charger, whichever is the most convenient. Remember to fuse the positive connections of the VSR.

If you only want to use the VSR for the reasons in post #1, you can fit a switch in the negative connection to disable it when not required.

 

[Buck Turgidson]

The Solar will charge the LP batteries anyway so you will not have solved your primary problem. You could rig a remote switch through a VRM such as the victron global link which has a remotely operated rely.
I decided not to do this and my 50w solar fully charged my house bank in a few days and is currently cycling each day. I will put a relay in next time I go to the boat.

 

[dune16]

The Solar will charge the LP batteries anyway so you will not have solved your primary problem. You could rig a remote switch through a VRM such as the victron global link which has a remotely operated rely.
I decided not to do this and my 50w solar fully charged my house bank in a few days and is currently cycling each day. I will put a relay in next time I go to the boat.
View attachment 180855

I was thinking of changing the solar charge settings over winter. Something like 13.6v bulk and 13.4v float so the batteries don't ever get fully charged and will have a small daily drawer on them from wifi and cctv. Do you think this would harm the lfp's being like this for a few months?

 

[dune16]

It would connect between the positive terminal of each engine battery.

You can make those connections at the batteries, the engine battery isolators, the engine terminals of the Argofets or the engine terminals of the three outlet mains charger, whichever is the most convenient. Remember to fuse the positive connections of the VSR.

If you only want to use the VSR for the reasons in post #1, you can fit a switch in the negative connection to disable it when not required.

Do you have a suitable vsr you'd recommend? Thanks very much

 

[Buck Turgidson]

I'm new to lithium so not the right guy to answer this unfortunately.

 

[geem]

I was thinking of changing the solar charge settings over winter. Something like 13.6v bulk and 13.4v float so the batteries don't ever get fully charged and will have a small daily drawer on them from wifi and cctv. Do you think this would harm the lfp's being like this for a few months?

That's how I will leave mine this winter. Make sure you have your mppt set to stop charging at about 5degC. If you charge below freezing you risk damage to the lithium

 

[PaulRainbow]

Do you have a suitable vsr you'd recommend? Thanks very much

Victron Cyrix 120a

 

[dune16]

Victron Cyrix 120a

One other question. If I left my 2 agm's fully charged and cut off from the engines so zero draw on them, would they be OK to go through the winter with no charging? I've read mixed messages on agm's on how long they can be left with no charge. Boat is in Croatia so no freezing weather. Thanks

 

[PaulRainbow]

One other question. If I left my 2 agm's fully charged and cut off from the engines so zero draw on them, would they be OK to go through the winter with no charging? I've read mixed messages on agm's on how long they can be left with no charge. Boat is in Croatia so no freezing weather. Thanks

Decent AGMs should be fine for the 3 months you mention in the OP.

 

[dune16]

Decent AGMs should be fine for the 3 months you mention in the OP.

Ok great, so perhaps I'm overthinking and can just leave the boat off shorepower and let the solar take care of the lfp. Thanks