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Old 13-02-2021, 13:10   #1
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Is they a way to wire with existing charging system?

Situation: 400amp house back has died and I'm considering installing a 280amp (homebuilt) LifePo3 with 200 amp BMS. We get by fine with ~100 amps/day in our coastal cruising but may want/need more in the future. Being simple minded and frugal I'm trying to:
  • Live with the charging sources already on board: Yanmar single belt 80amp factory alternator, 360W Solar w/ Midnight Kidd MPPT, 8K gen with 2Kw/100amp inverter/charger
  • Create a situation to expand/address shortcomings in the future if/as needed.

The main question >>> I can change the Midnite Kidd MPPT and Xantrex Freedom 100amp charger over to a LIFEP04 profile. Is there a way to keep the existing alternator setup by not having it directly charge the LifePo3? I'm thinking of wiring the alt. directly to the starting battery and just charging the LifeP04 by solar and generator. (we get a lot of sun here in Florida )

Second question >>> I have an existing BlueSeas ACR that currently connects the house to the starting bank when appropriate. If the existing ACR wiring was versed (i.e. starting >> house) and the alternator changed to charge the starting battery directly; if the BMS shuts down would that ruin the alternator or will the starting battery act as enough of a 'buffer' if the ACR had connected the two banks?

The current system is well installed with fuses in all the right places and very adequately sized wires. Is it possible to just reconfigure the rest of the wiring and not go thru the alternator/smart charging/B2B stuff now (realizing it's not optimal)?

Here is what I'm thinking (TIA for all suggestions):
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Old 14-02-2021, 17:17   #2
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Re: Is they a way to wire with existing charging system?

My knowledge is almost zero on this and I have just had a similar idea and would like to hear thoughts as well.


From my limited research I think it is a good idea to keep Load Bus and Charge Bus separated and have a split system.


My thoughts are for my boat:


Currently I have 880AH of AGM's being charged off:

1 x 400W Panel with MPPT
6 x 100W Panels With MPPT
2 x Engines (with own Start Batteries)
1 x Generator (with own Start Battery)

Trying to keep the cost down and keep it very simple:

Keep 1 x 220AH AGM which will be charged by the Engines & Generator but NOT Solar

Install 1120AH Lithiums (4P4S with 4 x BMS) which will be charged by the Solar on their own new charge bus.

Have a DC to DC Charger on its own new charge Bus from AGM to Lithium

Isolators etc would be installed where needed

The Load Bus (separate from any charge bus) would be from the Lithiums with the option to switch over to the AGM in an emergency

Starter Batteries would remain the same.
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Old 15-02-2021, 07:49   #3
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Re: Is they a way to wire with existing charging system?

Quote:
Originally Posted by Jim_B View Post
Situation:
Second question >>> I have an existing BlueSeas ACR that currently connects the house to the starting bank when appropriate. If the existing ACR wiring was versed (i.e. starting >> house) and the alternator changed to charge the starting battery directly; if the BMS shuts down would that ruin the alternator or will the starting battery act as enough of a 'buffer' if the ACR had connected the two banks?

The current system is well installed with fuses in all the right places and very adequately sized wires. Is it possible to just reconfigure the rest of the wiring and not go thru the alternator/smart charging/B2B stuff now (realizing it's not optimal)?

From everything I've read (my knowledge is theoretical, I'm in the midst of designing my own lithium system as well, see my post adjacent to this one), charging the start battery first will prevent damage to your alternator in case of HVD from the BMS. Given your factory 80amp Yanmar alternator w/internal regulator, this is the best way to get switched over to a Lithium house bank with minimal redoing of your system.

As you noted, the ACR would not charge the Lithium bank optimally, but more importantly it will not limit the current the house bank draws from the alternator. The high charge acceptance rate of the Lithium bank will likely overwork and burn out your unregulated alternator in short order. The ACR might work with an external regulator that will dial back your alternator, but the charge profiles and voltages will still differ between the house and start batteries.

The B2B charger instead can be programmed to deliver an optimum charging regiment for the Lithium bank, without overtaxing your alternator. With your standard 80amp alternator, you could conservatively go with a 30amp b2b charger and likely keep your alternator safe. You'll still be taking advantage of Lithium's high CAR and capacity compared to your old lead bank.

-Eric
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Old 16-02-2021, 15:32   #4
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Re: Is they a way to wire with existing charging system?

Thanks for the information. I've done more research and a B2B charger between the start and house bank seems like $250 well spent.

I assume there's no point having the ACR with a B2B?
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Old 17-02-2021, 07:07   #5
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Re: Is they a way to wire with existing charging system?

The B2B will take the place of your ACR. Remember that different manufacturers have different charge settings for their batteries, and you'll need to program your B2B voltage output not to overcharge the bank.
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Old 03-03-2021, 10:33   #6
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Re: Is they a way to wire with existing charging system?

I will second Eric's advice on the use of a B2B charger. This is definitely the way to go. You will need to design a dual DC bus topology to be able to separately disconnect charge sources in the case of a high voltage event and load sources in the case of a low voltage event. Make sure the BMS you end up buying is capable of doing such things. Those cheap Chinese "Daly BMS" products are not suitable for this kind of application. Read Nordkyn Design's excellent article on this topic.
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Old 03-03-2021, 20:08   #7
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Re: Is they a way to wire with existing charging system?

Spend the money to buy a quality DC to DC charger that has a remote on/off switching ability. Use a BMS such as the Electrodacus SBMS 0 that has the separate charging cut and discharging cut ability and there are a number of units listed in the installation manual that will work with the Electrodacus unit and diagrams on how to wire them. A DC to DC charger is really no different to an MPPT solar controller so the wiring is the same.
Next, how many amps charging are you expecting from the solar and alternator and gen set powered inverter/charger? If you were to use the Victron 30 amp DC to DC for instance, you can run multiple units depending on the charging input you are expecting and only run the ones that suit the charging at the time, say a single unit with only the alternator charging, but maybe 3 units with all the systems charging.
Simply wire all the charging systems you have now to the AGM start batteries and set the charger profiles to suit AGM, then power all the DC to DC chargers from the start battery. You should add a voltage sensing relay between the DC to DC chargers and the start battery to protect the start battery from excessively discharging it because that will shorten its life.

Reasonably simple to follow instructions for the Electrodacus unit and Dacian is always available via email to guide you through any sticky spots you might have not quite understanding just what he is getting at in the instructions.

No, I don't sell these units or get any money from Dacian for promoting his gear. I am testing these units in regards to incorporating them into the BMS off grid systems I design and install to give a lot more information via the phone or Ethernet or computer or what ever device suits your needs ..... the little screen sends me cross eyed after a few mins, but I'm getting old and blind so ......

T1 Terry
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