DC to DC chargers and Isolators

Blagger

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Oct 1, 2021
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2
Hi all,

I have a catamaran with 3 battery banks, one starter battery for each engine and one house bank of FLA batteries. Currently each alternator is wired to a large isolator with 2 input channels and three output channels. the three output channels go to each of the battery banks.

I am upgrading the house bank to Lithium Is it possible to avoid a lot of re-wiring to just disconnect the house bank from the isolator and add a DC-DC charger from the isolator to the house bank. This does mean i will only have one dc-dc charger and not two but it means it will receive power when either or both engines are running and also keeps the Alternators protected from the Lithium doing a dump when full as the alternators run to the isolator.

Thanks in advance
Joe
 

swampy

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Aug 29, 2020
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Timely question as this is exactly what I'm about to do. As far as I know it will work fine. It should avoid any kind of spike to the alternator when the BMS/and or charger cuts off the charging to the house bank, as the start batteries will absorb the momentary excess charge that was going to the lithium's, thus protecting the alternator.

I think... the other possible benefit is protecting the start batteries if you have separate "maintenance" solar panels for them. I have heard that a small solar panel to maintain a start battery can trigger the DC-DC charger to turn on, enabling the lithium house bank to completely drain the start battery. An isolator should prevent this. I believe some people install a manual shutoff switch for the DC-DC charger which could accomplish the same thing.

I'd be interested to hear other opinions on this though.
 

Smokin

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Sep 8, 2021
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145
If for some reason the bms cuts off the charge that doesn't seem to be an issue on your setup because the 2 other batteries would prevent a spike.
My thoughts are:
replace battery bank and leave everything as is.
(is there a voltage sensor wire attached to the house bank?)
 

Marinepower

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Apr 24, 2020
Messages
106
Hi all,

I have a catamaran with 3 battery banks, one starter battery for each engine and one house bank of FLA batteries. Currently each alternator is wired to a large isolator with 2 input channels and three output channels. the three output channels go to each of the battery banks.

I am upgrading the house bank to Lithium Is it possible to avoid a lot of re-wiring to just disconnect the house bank from the isolator and add a DC-DC charger from the isolator to the house bank. This does mean i will only have one dc-dc charger and not two but it means it will receive power when either or both engines are running and also keeps the Alternators protected from the Lithium doing a dump when full as the alternators run to the isolator.

Thanks in advance
Joe
I have been running my LFP bank directly off a battery isolator (victron ArgoFet). The alternator is regulated (Balmar) and set for a lithium charge profile (13.9v). The start batteries are essentially trickle charged when the the engine is running. Not ideal but seems to work. Most importantly I don't have a lot of solar and need the max I charge can get out of the alternator during the short engine run times. The DC_DC chargers just don't cut it in this regard as they have to be sized for lowest continuous alternator output.

If you run your engine a lot or if you have a lot solar, perhaps not an issue and DC-DC would be better.
 
Last edited:

TLJester

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May 24, 2020
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32
Curious what you do as I'm in the same boat 😉
Tempted to keep the old AGM bank and charge from the new LifePo4 bank with a 48v to 12v @30amp converter
 

Marinepower

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Apr 24, 2020
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106
Curious what you do as I'm in the same boat 😉
Tempted to keep the old AGM bank and charge from the new LifePo4 bank with a 48v to 12v @30amp converter
yes this too seems to be another strategy. Presumably the DC-DC charger can handle an alternator load dump if the BMS kicks in. I have not tried it but seems like it would work...
 

SV CAOAN

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Nov 7, 2021
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I have a catamaran also and it has a brand new solar 1200W and AGM X5 @170AH with victrom 150/100 mppt. I want to top up the engine batteries from the AGM. I'm planning on using a Renogy dcdc 40amp. Has anyone done this or have wiring suggestions?
 

Cheyne

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Aug 29, 2021
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On my cat I have Balmar 120 amp alternators and regulators set to AGM charging Optimum Red Tops batteries. On the Positive side of the master switch for the starter I have Victron 12/12 30 amp that connect my Lithium bank via the Lynx Distributor with a Circuit Breaker in between. I also have a Circuit Breaker between the Master Switch and the DC/DC charger that I use as a on/off switch.
 

willo

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Apr 8, 2020
Messages
389
With two AGM/FLA banks and a Lithium bank...
I would buy two DC-DC chargers. With the victrons you can set them to detect when the engine is running so you get the same behavior as using the isolator. You could still use isolators if you wanted to charge both lead banks from the engines - the victron is tunable to account for the voltage drop of something like an isolator or different chemistries.

I use a victron Orion Smart DC-DC to charge my camper off my truck. Engine run state detection works well. The bluetooth app works great. For just DC-DC conversion, I use their non isolated 24/12 converters. Those are dumb bricks with some minor adjustability. (I use 24v banks and need 12v for various bits.)
 

mainsheet

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Nov 13, 2021
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For what it is worth: At one of Victron's North American Training tour in Seattle last month, I asked one of Victron's instructor (and also a local distributor) at the event how I could setup my 100A Balmar alternator/ARS-5 regulator to charge a LifePO4 house bank and a AGM starter bank. He told me to have the alternator charge the LiFEPO4 bank directly with the alternator (controlled by the ARS-5 after reprogramming it for LiFEPO4, or invest in a new MV-614H regulator that's preprogrammed for LiFEPO4), then have the starting battery charged through the Victron's Orion DC-DC Smart charger. He mentioned that this the setup he built for one of his client recently with advice from Balmar.
 
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