Charging House & Starter Battery with One MPPT Controller - 1/2/Both Switch

[TJ11]

Hello. I am looking for some advice on charging both my house bank and starter battery with a single MPPT controller.



My current setup is as follows: 315ah Acid House Bank (Three 105 ah batteries) wired in 12v parallel. Single 100ah 12v acid starter battery. 380 watts of solar wired directly to the house bank, using a Victron 100/30 smart controller. The Victron does not have the ability to charge two battery banks.



I am considering adding a Victron Cyrix combiner to charge the starter battery with solar as well.


However, can't I simply move my 1/2/Both switch to "both", thereby creating one big parallel 12v bank and charge both the house and starter batteries with the solar each day?



I understand the risk of possibly draining both banks when leaving the switch on "both". However, my solar seems to be keeping up with the house bank demands nicely here in the Caribbean sun as I am on a float charge by early afternoon each day. I suppose I could switch the 1/2/Both back to the house only bank each night or when several cloudy days are present to make sure I do not drain the starter battery.


Thanks in advance for your input!

[tkeithlu]

The difficulty I see is the house and starter batteries being in very different charge states when you combine them. Might you supply the starter battery with an added solar panel?

Why are you needing solar to charge a starter battery? In simple rigs that is taken care of by an alternator on the engine. If that fails, it's time to get out the jumper cable and parallel the house to the starter to get the engine going again.

[TJ11]

Originally Posted by tkeithlu

The difficulty I see is the house and starter batteries being in very different charge states when you combine them. Might you supply the starter battery with an added solar panel?

Why are you needing solar to charge a starter battery? In simple rigs that is taken care of by an alternator on the engine. If that fails, it's time to get out the jumper cable and parallel the house to the starter to get the engine going again.

Great point. Thanks for the reply. I don't have much room for another panel dedicated to the starter. I also think I have plenty of solar for both banks. Agreed that the alternator will charge the starter no problem. I should have clarified that I leave the boat for months at a time and would like the solar to trickle charge both banks if possible.

[Stu Jackson]

Originally Posted by TJ11

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However, can't I simply move my 1/2/Both switch to "both", thereby creating one big parallel 12v bank and charge both the house and starter batteries with the solar each day?



I understand the risk of possibly draining both banks when leaving the switch on "both". However, my solar seems to be keeping up with the house bank demands nicely here in the Caribbean sun as I am on a float charge by early afternoon each day. I suppose I could switch the 1/2/Both back to the house only bank each night or when several cloudy days are present to make sure I do not drain the starter battery.

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Of course you can! I've always maintained that B is for Both and BACKUP. Like if you had a combiner and it failed (if you left your boat, instead of living on board, you'd most likely want to turn your main power switch 1-2-B off before you left).


You're there, so all you're doing is making the charging a management issue.


Good idea, costs nothing.


If you want to do it automatically, a combiner is a good way to do it, many different makes, my 1998 Yandina is still going strong.


Forget about batteries at different states. They always will be. The ONE constant is they always need a charge and will accept what you have since you are using them 24/7.


You have a good solution that costs you Zip!

[steamgoat]

Why not permanently separate the start battery and charge it with a Echo charge from the main bank,simple and not expensive.

[TJ11]

Originally Posted by steamgoat

Why not permanently separate the start battery and charge it with a Echo charge from the main bank,simple and not expensive.

Good point. I believe the Victron Cyrix combiner I have my eye on does essentially the same thing as an echo charger. I was looking for a simple solution with the "both" switch in case I don't get the combiner installed before leaving the boat for a few months.

[stormalong]

Originally Posted by TJ11

Good point. I believe the Victron Cyrix combiner I have my eye on does essentially the same thing as an echo charger. I was looking for a simple solution with the "both" switch in case I don't get the combiner installed before leaving the boat for a few months.

Using the both switch to keep the batteries charged is not a good idea unless you have an automatic battery charger on during your absence.

One battery bank will be slightly different from the other. There will be a constant current flow from the higher voltage battery bank to the other which will eventually weaken both batteries. That is why a battery combiner/voltage controlled relay is better. It only joins the batteries when the voltage rises to a level indicating that it is being charged.

There are many brands on these devices. Like Stu Jackson I have a Yandina, about the same age as his and still going.

[Stu Jackson]

Originally Posted by TJ11

Good point. I believe the Victron Cyrix combiner I have my eye on does essentially the same thing as an echo charger. I was looking for a simple solution with the "both" switch in case I don't get the combiner installed before leaving the boat for a few months.

New info, changes the answer.


Get a combiner, echo charger or any other VSR to charge both banks when you're away from the solar you have.


OR, since you won't be there, wire the banks together. Since there shouldn't (?) be any loads, it doesn't matter if the chemistry is different.


What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
http://forums.catalina.sailboatowner...d.php?p=742417 and http://c34.org/bbs/index.php/topic,9....html#msg70131

Making Sense of Automatic Charging Relays (2019)
https://marinehowto.com/automatic-charging-relays/

[PaulCrawhorn]

Yes, a good ACR like Blue Sea can close the connection based on sensing a charge source present from either side.

The ML is fine for 500A for self-jumpstarting and lead does not draw much anyway.

Do not use a manual switch.

If you put all sources direct to House, then a little Echo Charge or the like will keep Starter topped up from there.

[ColinIOM]

Hi, Personally I would not use the OFF/A/B switch to charge your engine battery, sure as god made little apples, the one time you needed to start your engine the batteries would be down. Thats the whole idea of that switch and having a dedicated engine battery.

Sterling Brand in the UK produce top quality chargers of all kinds and make a small 3amp “battery Maintainer” that would do your job perfectly for about £80. Basically it is connected to both sets of batteries monitoring their respective voltages and only “top up” the engine battery from the house batteries when they are we’ll charged.
Please see the links below. The first one gives a great description of its operation.
All the best
Colin

https://cdn.shopify.com/s/files/1/06...tainer.pdf?745

https://sterling-power.com/search?ty...ery+maintainer

[Paul Carey]

Stu is on the right track , Voltage Sensitive Relays (VSR's) have never been cheaper ; < £20 each in UK direct from China inc shipping & with that in mind I would also use them between the 3 house batteries ,

[Flatswing]

Gotta agree with the green frog. If your start battery is isolated, drain is minimal, engine alternator will take care of charging. Trucks & heavy equipment often sit for months with no external charging no problem. Unless the manufacturer’s charging parameters are the same for start bank & your house bank, combining them for months while you are away may overcharge the start bank, perhaps shortening its life.

I would charge your house with the solar, leave the start isolated, combine (with the 1/2 switch if needed) for 1st start after long absence.

[sailcrazy]

We've been doing just that for the last 10+years! We use Trogen T-105s for our house bank. The Victron conroller(solar) and the windgen contoller, along with the eng alternator all feed that bank. I installed a Banmar Duo-Charge between the house bank and the start battery, so as the start batt gets a little discharged, it is automatically recharged by the house bank+Duo Charge. The alternator on my genset also feeds the start battery (a regular sealed car battery). My batt monitor allows me to check on both charge states, but it's never been a problem, and the start batt is always fully charged-with no action required on my part. System seems to work well! By the way, we use the same start battery for both engine and genset charging.

[Lazydoh]

I wanted to be able to charge the house and starter banks with my one solar panel. I found one controller that would charge both, priority house.
EPEVER DuoRacer MPPT Dual Battery Solar Charge Controller 30 amp 12V 24V Auto - Negative Ground Solar Controller.
So far it's working fine both during the season and keeping the batteries charged on the hard.

[RSB333]

I use the echo charger which automatically sends juice to the start battery once the house bank is full - every afternoon in the summer.
RSB333