VSR, Two Batteries & Charging

[markleuty]

Hi

I used to have a 1/2/Both but changed over to a VSR and separate switches last year.

What confuses me is why the Starter Battery doesn't get seriously over charged?

If I've been sailing all day, using various bits of electricity (auto-helm, GPS, laptop, fridge etc etc), start the engine for a 10 minute trip into the marina, then stop then engine and put on shore power.

Immediately, the VSR trips in and the charge is being sent to both batteries. The House battery is well down and the Engine battery has hardly had any juice sucked out of it.

The charger goes through its nice 3 or 4 phase charge routine, but surely this is most suitable for the House battery and the Engine battery is getting a wad load that it doesn't need.

Sorry if the answer is obvious, but it's been baffling me for a while.

Thanks

Mark

 

[sailorman]

the vsr cut-in after a predetermined time / voltage thereby linking both banks & equalizes the level to both banks you cant over charge the engine bank it will only take what it needs

 

[Anthony]

Re: VSR, Two Batteries & Charging

the short / simplified answer is that as the start battery gets charged its internal resistance rises, and thanks to good old ohms law, it 'takes less charge'.

It gets a bit more complicated than that, but the simplified solution works for most people.

Ants

 

[markleuty]

Re: VSR, Two Batteries & Charging

That makes sense.

Old Mr Ohm has a lot to answer for..

Thanks

Mark

 

[Fr J Hackett]

Re: VSR, Two Batteries & Charging

As soon as the system begins to recieve charge it will be directed to the engine start battery as soon as that battery is fully charged the relay will be activated and the charge will then be diverted into the house battery. The system thus ensures that the engine battery always takes priority and is fully charged after which current is diverted to the other bank at no time do both banks recieve charge. In effect unless the engine battery has been seriously depleted for whatever reason it will charge up very quickly and the house bank will then soak up the alternator output.

 

[sailorman]

Re: VSR, Two Batteries & Charging

the Victron Battery Coupler senses both banks @ once. it has a voltage sensing as well as a 10 minute time delay.
it works even if a battery charger is coupled into the domestic bank with the engine switched off, it senses the domestics are full or 10 mins elapsed then it pulls in the engine battery & charges both banks

 

[Playtime]

Re: VSR, Two Batteries & Charging

I also changed to a VSR a year or so ago. Initially I was impressed - it did what it said on the tin. However, during an extended cruise, when the house battery was low, I found that the relay cycled i.e. clicked in and then immediately dropped out. The VSR was wired as recommended i.e. the engine battery (80 AH) was the 'default' and the house battery (280AH) was switched in when the engine battery reached 13.8V.
After some head scratching I concluded that the VSR was cycling because the house battery was pulling the voltage below the VSR drop out voltage as soon as it was switched in. When the VSR dropped out, the engine battery was then immediately back to 13.8V so the VSR switched in the house battery again etc. etc.
The simple solution was to swap the wiring the make the house battery the default. The engine battery is then switched in when the house battery reaches 13.8V and there is no cycling.
I appreciate that there is a risk the engine battery could fail to charge (if the house battery is very low and never reaches 13.8V) but the risk is small, especially with a decent alternator set up.

 

[sailorman]

Re: VSR, Two Batteries & Charging

the victron gets over that by sensing both banks all the time it costs under £80 & very easy to fit. only 3 wires, 1 neg then one pos to each bank

 

[Playtime]

Re: VSR, Two Batteries & Charging

The Victron sounds like the complete solution. I'll seriously consider it if/when the BEP VSR fails (from cycling too much, no doubt)!

 

[sailorman]

Re: VSR, Two Batteries & Charging

Victron Cyrix

 

[halcyon]

Re: VSR, Two Batteries & Charging

How does a VSR work ?

A simplified answer.

To start, a battery has three voltage ranges, open circuit ( off load ), discharge, and charge. A low battery when put on charge will go to approximatley 13 volt, the voltage rise as the battery is charged. If you start discharging the battery it will fall below 13 volt.

Now start the engine, normally the voltage will rise fast. Now the VSR is set to come in at a voltage, normally around 13.8 volt. But can be adjusted to suit a particular boats charging system.

The relay now engages, and connects the service battery to the engine battery.

The service battery is at a lower capacity, and thus lower internal resistance, so the charge takes the least line of resistance, and flows through the service battery. As the resistance is lower, the terminal voltage you see will fall, but not normally below the 13 volt mark.

At this point, the voltage is to low to charge the engine battery, and not low enough to cause a serious discharge. The full alternator output now flows to the service battery.

As the service battery charge level comes up, so does the terminal voltage, and it will reach a level where the engine battery starts to take a charge again. All the batteries now act as one large bank, and take a charge as each battery requires.

When you stop the engine, or loose charge, the voltage will fall to the lower voltage range, and the relay will drop out at around 13 volt. Thus isolating both battery banks.

That is the simple answer, in real life it's a bit more complex. By using this principle you can charge three / four banks in a programmed cycle, interface temp sensing etc.

Brian

 

[markleuty]

Re: VSR, Two Batteries & Charging

Brian

Thank you.

Mark

 

[lumphammer]

Re: VSR, Two Batteries & Charging

Looking at the data sheet the following line

"The Cyrix-i 12/24-100 has a dual power supply. It will therefore also close if the voltage on one battery is too low to operate
the Cyrix."

suggests to me that if one battery voltage drops then the relay will operate joining the two batteries together. Doesn't this run the risk of draining the engine start battery?

 

[Playtime]

Re: VSR, Two Batteries & Charging

My understanding is that the relay will only operate to combine the 2 battery banks when the voltage sense on either bank is ABOVE the threshold i.e. greater than 13.6V or thereabouts. The advantage of this is that you can have separate chargers for each battery bank; then, if any charger (alternator, shore power, wind generator etc.) is producing more than the threshold the relay will operate and the banks will be connected together. When the charging source drops below the drop out threshold (say 12.8V) then the banks will be isolated again.
If my understanding is not right, I'm sure Sailorman will be along shorty to correct it!

 

[sailorman]

Re: VSR, Two Batteries & Charging

Hole in 1
mine works a treat
i did have a conventional vsr fitted by the previous ( first ) owner when it went Phut i fitted the Cyrix,

 

[halcyon]

Re: VSR, Two Batteries & Charging

[ QUOTE ]
Looking at the data sheet the following line

"The Cyrix-i 12/24-100 has a dual power supply. It will therefore also close if the voltage on one battery is too low to operate
the Cyrix."

suggests to me that if one battery voltage drops then the relay will operate joining the two batteries together. Doesn't this run the risk of draining the engine start battery?

[/ QUOTE ]

No, all it means is the relay coil is powered from both batteries.

Hell, we introduced that back in 1982, together with dual sensing. /forums/images/graemlins/smile.gif

Brian