Multiple DC-DC Chargers

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serenity asked May 20, '23

Multiple DC-DC Chargers

Background: We are upgrading our house battery banks (2) on our sailing catamaran with Lithium. With two engines we will be installing a pair of Victron DC-DC 30A Isolated Chargers, one on each starter battery/alternator. Our two house battery banks come together at a bus bar after a battery switch that allows us to select Bank 1/Bank 2/Both for our 12V needs. Space is limited as to where I can install the chargers. I have located places for both but they are not near one another. Nor will the runs from either charger be the same length given the positions of each. The plan is to aggregate output of the two chargers downstream into the same busbar where our 2400W solar array connects to provide current for charging the banks.

Questions: Will a difference in distance between the starter batteries and the Chargers make a big deal? (obviously we will use the correct wire size for each run. I believe given the distances 6AWG is appropriate) Will the disparate length of the two output runs create an issue on the aggregation side with current? I assume technically the only time the chargers will be working in concert and provide greater than ~30A of current is when both engines are running. Aside from a longer timeframe to charge either bank, is there anything wrong with this plan? Are we missing anything?

Thank you.

battery charging BMV Battery Monitor Lithium Battery orion dc-dc dc system

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Answer 1 · 2023-05-21T00:05:10Z

Sarah answered · May 21, 2023 at 12:05 AM

Hi @Serenity Obviously the goal is the get the chargers as close to the batteries as possible to minimise voltage drop. In this case you can tweak the output voltage of the orions to compensate for any differences. You would probably need two shunts, one on each Orion, to do it properly. Also be aware that the Orions do get quite hot and will need to be well ventilated. It also helps to consider that the Orions will go into bulk each time the engines are started - not a huge problem per se but it can have some unintended impact on the solar controllers.

On our cat we have three shunts. One Lynx BMS SOC, and two smart shunts to measure alternator current, and load. Very happy with the data we get. You could temporarily repurpose the load shunt to balance the alternator output. We then use the auxiliary battery voltage on the smart shunts to measure the starter port and starboard battery voltages.

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serenity commented · May 25, 2023 at 09:42 PM

Thank you Sarah. Given the fact that we have a catamaran and that each house battery bank, 1 & 2, are in separate hulls and then joined together in the primary electrics area, my options are somewhat narrow.

I have determined that I can place the DC-DC charger units either half way between each starter battery or have one close to the starter battery and the other a decent distance, 20' or so, away. This would place both chargers near each other. However, the space is limited and may become rather warm. I have spec'd a couple of fans to cool the chargers as I have read exactly what you conveyed, they get very warm! This would place the aggregated amperage nearest the same point where the solar and charger connections presently reside. Otherwise I would have the port charger output run approximately 20' to the aggregation point and the stbd output within 2'-3'. Either way, the port house battery bank remains 20' from the aggregation point.

I've attached a diagram to this response of my current configuration along with the planned DC-DC charger configuration that will replace the ACR's. Any thoughts or insight from you or anyone reading this is greatly appreciated.

Serenity Electrics.pdf

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serenity-electrics.pdf (236.5 KiB)

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