split charge relay (vsr) with solar?

[skyflyer]

I have (fitted by PO) a split charge diode device which allows engine alternator to charge both batteries without either battery being able to discharge/recharge to/from the other -in effect a 'one way valve' for alternator current into the 2 batteries.

I am thinking of replacing with a VSR split charge relay so that the batteries will automatically parallel when voltage to either is greater than (say) 13.8v

But I also am about to fit a solar panel which will connect through an MPPT controller.

Will the output voltage of the MPPT controller be enough to trip the VSR so both batteries get charged?

If so what would be a suitable VSR to buy? I am concerned that if one battery becomes very discharged, as soon a voltage on other goes up the relay will open allowing a huge current to pass?

Controller is an Epever 20A

TIA

 

[VicS]

I have (fitted by PO) a split charge diode device which allows engine alternator to charge both batteries without either battery being able to discharge/recharge to/from the other -in effect a 'one way valve' for alternator current into the 2 batteries.

I am thinking of replacing with a VSR split charge relay so that the batteries will automatically parallel when voltage to either is greater than (say) 13.8v

But I also am about to fit a solar panel which will connect through an MPPT controller.

Will the output voltage of the MPPT controller be enough to trip the VSR so both batteries get charged?

If so what would be a suitable VSR to buy? I am concerned that if one battery becomes very discharged, as soon a voltage on other goes up the relay will open allowing a huge current to pass?

Controller is an Epever 20A

TIA

Victron Cyrix perhaps https://www.victronenergy.com/battery-isolators-and-combiners/cyrix-battery-combiners

Victron also offer some good MPPT controllers

What you are suggesting is a normal VSR set up. but when the voltage on one ( battery) goes up the relay will CLOSE .....( at 13 .7 volts for the Cyrix) ... to connect the other. This will happen whatever the charging source; alternator, solar, charger etc

BUT before Paul Rainbow picks up this topic post some more detail. Eg battery bank sizes and alternator detail

 

[simonfraser]

The solar will trigger your VSR / relay.
That’s no bad thing, but it will mean that when you start your engine the house battery will feed the starting batteries.
If you have a big engine there will be a lot of current flow through the VSR / relay, just saying.

 

[PaulRainbow]

Victron Cyrix perhaps https://www.victronenergy.com/battery-isolators-and-combiners/cyrix-battery-combiners

Victron also offer some good MPPT controllers

What you are suggesting is a normal VSR set up. but when the voltage on one ( battery) goes up the relay will CLOSE .....( at 13 .7 volts for the Cyrix) ... to connect the other. This will happen whatever the charging source; alternator, solar, charger etc

BUT before Paul Rainbow picks up this topic post some more detail. Eg battery bank sizes and alternator detail

Morning Vic

 

[Stemar]

Get yourself a dual battery solar controller. I've had one for years with a relay split charger and had no problems. It charges the engine battery until full, then turns its attention to the domestic, so I've always got plenty of go to start the engine if all else fails.

 

[halcyon]

The solar will trigger your VSR / relay.
That’s no bad thing, but it will mean that when you start your engine the house battery will feed the starting batteries.
If you have a big engine there will be a lot of current flow through the VSR / relay, just saying.

Not if you have the option to interface VSR to the starter motor, dropping out VSR before starter motor kicks in, stopping trying to start the engine from solar panel, mains charger or the charging system.

Brian

 

[PaulRainbow]

Get yourself a dual battery solar controller. I've had one for years with a relay split charger and had no problems. It charges the engine battery until full, then turns its attention to the domestic, so I've always got plenty of go to start the engine if all else fails.

Why fit a dual output solar controller and a VSR ?

The VSR does not charge the engine battery until full. When whatever charging source that is connected to the engine battery (usually the alternator) starts to charge the relay will close, as it senses the alternator voltage.

With a solar controller connected to the domestic bank the VSR will close when the batteries reach a per-determined voltage or the output from the solar controller reaches that same per-determined voltage, whichever comes first. So there is no point fitting a dual output controller if you have a VSR.

 

[halcyon]

Why fit a dual output solar controller and a VSR ?

The VSR does not charge the engine battery until full. When whatever charging source that is connected to the engine battery (usually the alternator) starts to charge the relay will close, as it senses the alternator voltage.

With a solar controller connected to the domestic bank the VSR will close when the batteries reach a per-determined voltage or the output from the solar controller reaches that same per-determined voltage, whichever comes first. So there is no point fitting a dual output controller if you have a VSR.

Because the VSR relay coil can consume a good proportion of the solar charge current, unless big panel. VSR after battery isolators, twin solar controller before, taking VSR out of circuit when boat is unattended.

Brian

 

[William_H]

A VSR has by definition a relay with power to it's coil which will probably waste about .3 amp when activated. Not to mention a small current to the sensing circuit at all times. perhaps 10ma. Now with a large solar panel set up this loss would be acceptable but not with a small panel. Also a small panel may not bring a battery up above the VSR trip point when charging. All this meaning that for small panel say less than 100w (a guess)(or low light) you would be better off to fit a solar regulator with dual output. So you can leave power (to the VSR turned off).
Alternatives are to fit another small panel for engine battery with or without a regulator. or fit another regulator to the one solar panel to feed the other battery.
OP shouyld leave the split charge diodes for the alternator as is if they are working satisfactorily. ie there is no voltage drop or the voltage drop is allowed for in a higher voltage regulator or battery sensing. good luck olewill

 

[PaulRainbow]

The Victron Cyrix Vic mentioned uses less than 4ma when open. If it's a small panel that won't bring the battery up to the trip point it's a) a waste of time as it isn't fully charging the battery and b) it isn't closing the VSR so will be using less than 4ma.

If the solar panels are putting out enough to close the VSR a small loss from the VSR will not make any difference when the boat is unattended.

 

[halcyon]

The Victron Cyrix Vic mentioned uses less than 4ma when open. If it's a small panel that won't bring the battery up to the trip point it's a) a waste of time as it isn't fully charging the battery and b) it isn't closing the VSR so will be using less than 4ma.

If the solar panels are putting out enough to close the VSR a small loss from the VSR will not make any difference when the boat is unattended.

Think that was what I said.

Brian

 

[skyflyer]

Hmm - and i thought I'd asked a simple question!

The way I understand it the VSR senses voltage which is NOT quite a perfect indicator how full the battery is, except when the battery has been allowed to rest at a steady state. So yes, when the battery is drained it will 'drag down' the voltage but as it gets closER to being full, the voltage will steadily build until it is similar to the output voltage of the solar controller (which i think is 13.8v)
So if VSR closes at (say)13.7 v then the battery could well be less than full.
But that is not my concern - basically the idea of the solar is to keep the leisure battery charged up - in fact it is primarily to offset the drain from the fridge. At 100W it wont achieve that but it will extend the time between needing to run the engine or plug in shore power.
So my thinking is simply that once the leisure battery is almost full, why not "spill over" the charge to the engine starter battery. (which, see below, tis at the moment also a back-up leisure battery)
Problem (potentially) seems to be that if the leisure battery is near empty and if no or little sun, then the next engine start will see the VSR open as soon as the alternator starts pumping current and there could be a large current run from starter to leisure battery through the VSR.
Hence the plan to keep the spilt charge diode (which is compensated for by volt and temp sensing by advanced charging system) so the alternator volts goes to both batteries.
So I've sort of answer my own question now; I only need a single sense VSR (leisure to starter) and if I keep the spilt charge diode theres no worry about large current flows.
Its actually slightly more complex as my (factory standard) set up is two 180Ah batteries with a 1/2/Off switch so either can be designated as leisure or starter. Plan this year is to parallel them to make 360Ah then add a small starter battery (physically small as the compartment is tight on space) that will start the 3GM30F. I can always use the leisure bank in an emergency.

 

[skyflyer]

Just done a practical test at home to demonstrate:

Battery voltage at rest 12.2 v (nominally 50% discharged)
Connect 100w solar panel, which in evening sun, produces 27v and about 1.4 A
This is then converted to 14.4v and 1.8A into the battery
A VSR would thus presumably sense 14.4v across the terminals and close the contact.s?

 

[pvb]

Its actually slightly more complex as my (factory standard) set up is two 180Ah batteries with a 1/2/Off switch so either can be designated as leisure or starter. Plan this year is to parallel them to make 360Ah then add a small starter battery (physically small as the compartment is tight on space) that will start the 3GM30F. I can always use the leisure bank in an emergency.

That's a good plan. There's been lots of theory in the replies so far, but in practice your engine battery (if properly isolated) is almost always going to be fully charged as a result of normal motoring. So you could leave your existing split charge diode and simply connect your solar to the domestic bank (which is where you really need the charge). No need for a VSR.

 

[BabaYaga]

Problem (potentially) seems to be that if the leisure battery is near empty and if no or little sun, then the next engine start will see the VSR open as soon as the alternator starts pumping current and there could be a large current run from starter to leisure battery through the VSR.

I do not think that current will be any larger than at most the maximum output of the alternator, which the VSR must be rated for. What could occur in that situation is VSR 'chatter', but many claim this is not a problem with modern units...

Plan this year is to parallel them to make 360Ah then add a small starter battery (physically small as the compartment is tight on space) that will start the 3GM30F. I can always use the leisure bank in an emergency.

Good plan!

 

[halcyon]

Hmm - and i thought I'd asked a simple question!

The way I understand it the VSR senses voltage which is NOT quite a perfect indicator how full the battery is, except when the battery has been allowed to rest at a steady state. So yes, when the battery is drained it will 'drag down' the voltage but as it gets closER to being full, the voltage will steadily build until it is similar to the output voltage of the solar controller (which i think is 13.8v)
So if VSR closes at (say)13.7 v then the battery could well be less than full.

Forget the idea o switching at full battery level, the switching voltage originally was 13.6 volt, which was the regulation voltage, full recharge voltage. When alternators went to 14.0 / 14.4 volt we increased sense voltage to 13.7/13.8 volt, around 60% recharge level. back when we started on VSR's we only had the old MD1/2/3 a's etc, not good starters at times, so the initial cut in voltage ( 13.6 ) allowed some recharge to engine battery before the service.

The critical values when recharging is that the alternator has reached the regulation voltage ( max voltage ) and the charge amps are down low, say 2 amps, this means the battery is as full as you are going to get it. Depending on voltages this could be 80/90%, charge current will slowly get lower as the voltage remains stable, so yuo only burn fuel.

The danger with solar and VSR is that the service bank is normally larger than engine, if VSR is engaged it will pull current from both banks, which could be mainly service bank initially pending contact drop out.

Brian