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Re: Lifepo4 Batteries
Posted: August 9th, 2024, 12:04 pm
by mikesparker
Midnightsun wrote:QR_BBPOST Not sure why you took out the disconnects. I used the exiting one for my LifePo4 house bank and the other 2 for the start batteries remained unchanged. In my case I did not have 1/2/all disconnects, only on/off.
I can see why you would want to change/remove yours if they were able to combine lithium with lead acid just for safety reasons. That being the case, I would just install on/off switches where the old ones were or anywhere as long as you have good access. ACR between the starts is no issue. I did the same except I am using the original factory isolator to perform the same function.
I took out the disconnects because 1) they did, indeed, connect the LFP and start banks, 2) there were literally 10'+ cable runs to where they were. I'll re-use them in a better location...they're on/off only but were wired with the ACRs so that I could combine them if needed.
So I'll need one ACR for each start battery since they're 'directional', correct?
Re: Lifepo4 Batteries
Posted: August 9th, 2024, 12:38 pm
by Midnightsun
Combiners are directional, ACRs, no. Only need one between the 2 start banks. See here.
https://www.bluesea.com/support/article ... _Explained
Re: Lifepo4 Batteries
Posted: August 9th, 2024, 1:09 pm
by mikesparker
Perfect! Thanks again (again)...lol
Re: Lifepo4 Batteries
Posted: August 9th, 2024, 1:16 pm
by Midnightsun
Let me elaborate on this. A dual sensing ACR is better on a twin engine setup since it senses a charge from either alternator to connect the 2 batteries. If it is not a dual sensing, you do not have the backup of the second alternator IF the sense side is on the faulty alternator.
Re: Lifepo4 Batteries
Posted: August 9th, 2024, 2:37 pm
by km1125
I would have a separate on/off going directly to the inverter and one for the main DC loads, so you can disable the inverter entirely and still have normal flow to all the rest of your DC loads.
When I read "Both engines ground to one start battery, then cabled to the aft LPF, the fwd LPF, the 2nd start battery and then to the class T.", does that mean there's a fuse on the negative side?? That would be unusual. You can still a shunt in there somewhere if you want to track/measure loads, but having a fuse there is very unusual (although not entirely unheard of). I'm also wondering if these are daisy-chained as described, or if they really just tie into a common negative buss bar (which would be my preference!).
Re: Lifepo4 Batteries
Posted: August 10th, 2024, 7:33 am
by Midnightsun
I'm also wondering if these are daisy-chained as described, or if they really just tie into a common negative buss bar (which would be my preference!).
Agreed, common ground buss bar is the preferable way to go.
Re: Lifepo4 Batteries
Posted: August 10th, 2024, 12:27 pm
by mikesparker
km1125 wrote:QR_BBPOST I would have a separate on/off going directly to the inverter and one for the main DC loads, so you can disable the inverter entirely and still have normal flow to all the rest of your DC loads.
When I read "Both engines ground to one start battery, then cabled to the aft LPF, the fwd LPF, the 2nd start battery
and then to the class T.", does that mean there's a fuse on the negative side?? That would be unusual. You can still a shunt in there somewhere if you want to track/measure loads, but having a fuse there is very unusual (although not entirely unheard of). I'm also wondering if these are daisy-chained as described, or if they really just tie into a common negative buss bar (which would be my preference!).
I like the disconnect idea...I'll do that!
The grounds ARE daisy-chained at the moment only because I didn't have the bus bar yet. So I'll go from both engines to bus bar, then each battery to bus bar?
I DID hook the ground to the Class T...I was tired...
Thanks for the catch!!
Re: Lifepo4 Batteries
Posted: August 15th, 2024, 2:42 pm
by mikesparker
Potentially dumb question...where do I hook up my ACR in relation to the DC-DC chargers to gain redundancy?