0 volt drop splitter or current limiting voltage sensing relay?

[wipe_out]

My boat currently has two batteries and a 1-2-all-off switch to manage them.. I am thinking about changing this to have an engine start battery and a house battery so I don't have to think about it..

The two options I am weighing up seem to be the 0 volt drop splitter or the current limiting voltage sensing relay.. These both seem similarly priced and functionality is similar so having a hard time choosing between the two.. The splitter is obviously complete isolation which the relay means some of the engine battery power can be used but not too much that I can't start the engine..

I can't decide which is better..

or is there something else I have missed that is a similar cost or even a little more but better functionality? Seems to me the next step is battery to battery chargers or alternator to battery chargers but they are quite a lot more expensive with little real gain that I would see as useful..

What do you have?

 

[pvb]

The two options I am weighing up seem to be the 0 volt drop splitter or the current limiting voltage sensing relay.. These both seem similarly priced and functionality is similar so having a hard time choosing between the two.. The splitter is obviously complete isolation which the relay means some of the engine battery power can be used but not too much that I can't start the engine..

I can't decide which is better..

or is there something else I have missed

Why not simply use an ordinary VSR, rather than a current-limiting VSR?

 

[halcyon]

The splitter is obviously complete isolation which the relay means some of the engine battery power can be used but not too much that I can't start the engine..

Can you expand on the above statement, you may have a miss-understanding.

Two advantages with a relay, depending on spec, is emergency engine start from the service bank, and bi-directional charge if you fit solar panels.

Brian

 

[VicS]

Not sure that I can see the advantage of a current limiting VSR over an ordinary VSR in a simple situation.

You still have to decide between an ordinary VSR and a low loss electronic device such as Driftgate's X-Split though.

A small advantage, perhaps, of a Sterling Alternator-Battery charger is that it gives enhanced charging of the house battery but if the house battery is adequately sized maybe even that advantage is lost

 

[halcyon]

Not sure that I can see the advantage of a current limiting VSR over an ordinary VSR in a simple situation.

What are you classing as current limiting ?

Brian

 

[wipe_out]

Can you expand on the above statement, you may have a miss-understanding.

Two advantages with a relay, depending on spec, is emergency engine start from the service bank, and bi-directional charge if you fit solar panels.

Brian

As I understand it the 0 volt drop splitter takes the alternator charge and splits that to the two battery banks.. Neither batter bank can use the power in the other at all.. They are completely isolated.. With the relay the "house" side can use the engine battery power as well until the voltage drops below ~13v.. So there is aome shared load across the two batteries.. Have I got something wrong?

 

[wipe_out]

What are you classing as current limiting ?

Brian

This..
http://www.shop.sterling-power.com/acatalog/Current_Limiting_Voltage_Sensitive_Relays.html

So that the relay won't have issues if for example an inverter is added and there are high load spikes with electrical appliances..

 

[halcyon]

This..
http://www.shop.sterling-power.com/acatalog/Current_Limiting_Voltage_Sensitive_Relays.html

So that the relay won't have issues if for example an inverter is added and there are high load spikes with electrical appliances..

I'm having a thick night here Vic, when you say high load, what amperage, ?

Brian

 

[pvb]

With the relay the "house" side can use the engine battery power as well until the voltage drops below ~13v.. So there is aome shared load across the two batteries.. Have I got something wrong?

With an ordinary VSR, single-sensed on the engine battery, the house battery can only draw current when the engine battery is being charged. If it isn't being charged, the voltage would be below 13v and there'd be no connection.

 

[halcyon]

As I understand it the 0 volt drop splitter takes the alternator charge and splits that to the two battery banks.. Neither batter bank can use the power in the other at all.. They are completely isolated.. With the relay the "house" side can use the engine battery power as well until the voltage drops below ~13v.. So there is aome shared load across the two batteries.. Have I got something wrong?

Yes when you stop the engine you can supply some domestic load from the engine battery. But if you draw say 5 amp, the relay will drop out in 5 - 10 seconds, so you could loose 0.01 of a amp hour, or with a 100 amp battery, 0.01% capacity.

The VSR is fail safe, any fault or failure will still maintain engine battery charge, you can charge the engine battery from a charge source on the service battery, and start the engine from the service battery with it. So has many advantages, that offset the 0.01% of capacity lose while it isolates the batteries.

Brian

 

[wipe_out]

Yes when you stop the engine you can supply some domestic load from the engine battery. But if you draw say 5 amp, the relay will drop out in 5 - 10 seconds, so you could loose 0.01 of a amp hour, or with a 100 amp battery, 0.01% capacity.

The VSR is fail safe, any fault or failure will still maintain engine battery charge, you can charge the engine battery from a charge source on the service battery, and start the engine from the service battery with it. So has many advantages, that offset the 0.01% of capacity lose while it isolates the batteries.

Brian

I see.. So really in terms of "available" capacity to the house side when the engine is off there is no difference between the splitter and the VSR..

What are the advantages/disadvantages of a relay vs one of these http://www.shop.sterling-power.com/acatalog/12V.html

Only difference I can see so far is the reverse charging functionality of the VSR.. And the non-mechanical nature of the splitter..

 

[pvb]

I see.. So really in terms of "available" capacity to the house side when the engine is off there is no difference between the splitter and the VSR..

What are the advantages/disadvantages of a relay vs one of these http://www.shop.sterling-power.com/acatalog/12V.html

Only difference I can see so far is the reverse charging functionality of the VSR.. And the non-mechanical nature of the splitter..

Although VSRs are mechanical, they are very reliable, and far cheaper than the Sterling product you're considering.

If you really only have 2 batteries, one start and one domestic, you'd be far better to spend your money on a second domestic battery and an inexpensive VSR. The improvement in charge efficiency and endurance will be well worthwhile.

 

[wipe_out]

Although VSRs are mechanical, they are very reliable, and far cheaper than the Sterling product you're considering.

If you really only have 2 batteries, one start and one domestic, you'd be far better to spend your money on a second domestic battery and an inexpensive VSR. The improvement in charge efficiency and endurance will be well worthwhile.

The Sterling VSR's aren't a lot cheaper than the 0 volt drop splitter which is why I was evaluating them against each other.. What other brands of VSR's could I consider that are good and reliable?

In terms of amperage ratings on the VSR, is it best to get one that is higher than the expected maximum load? So for example if fitting a 2000w inverter that will theoretically pull about ~170A would I put in a 200A VSR (assuming not using the current limiting VSR that would shutdown in an overload condition)?

Thanks for your input by the way..

 

[halcyon]

In terms of amperage ratings on the VSR, is it best to get one that is higher than the expected maximum load? So for example if fitting a 2000w inverter that will theoretically pull about ~170A would I put in a 200A VSR (assuming not using the current limiting VSR that would shutdown in an overload condition)?

Where are you getting the 200 amp from ?

The only time you will see excessive load through the VSR is from the alternator, if you run the inverter, in this case it would be limted to alternator output.

Brian

 

[wipe_out]

Where are you getting the 200 amp from ?

Well if the house battery is low/flat and the engine battery is full and the engine is running so the VSR is closed and someone switches on something with a big load on the inverter it will pull the current from the engine battery and alternator through the VSR.. If the inverter is 2000W, at max load excluding inefficiency and cable losses it will pull ~167A (including cable loss and inefficiency this would be higher).. If the VSR is a 100A unit it would probably sustain a spike of 167A but at constant load it would probably burn out..

This is the scenario that current limiting VSR's protect against and splitting diodes/charge splitters don't have to worry about because the two batteries are completely isolated..

 

[JimC]

.. What other brands of VSR's could I consider that are good and reliable?

Victron and BEP are probably the most widely used makes.

http://www.victronenergy.com/battery-isolators-and-combiners/cyrix-battery-combiner-kit/

http://www.bepmarine.com/home-mainmenu-8/product-269/125-amp-voltage-sensitive-relay-vsr-

I use a Victron Cyrix which has some additional circuitry that prevents the relay contacts chattering under certain conditions. Either will give good results and avoid the wastage of alternator power that comes with diode splitters. It's worth noting that, even when some form of smart regulator is used to boost the charging voltage to overcome the losses in a diode splitter, power is still being uselessly dissipated in the diodes and this power can only be generated by burning diesel and transmitted via increased stress in the belts, heating of the alternator etc. It's not for nothing that diode splitters are mounted on big heatsinks.

The Victron will switch 120 amps and conduct twice that when the contacts are closed. This should cope with anything you are likely to throw at it. It's easily started my 2GM20 when I've experimentally used the Victron's capability of paralleling the batteries for emergency starting with the engine battery disconnected, so all the starter motor current is coming from the domestic battery and going through the VSR!

 

[William_H]

If you buy a VSR which can within itself carry starter currents for emergency engine start then inherently the relay should carry any sort of charge current. If you buy a simple VSR without this facility then you need another emergency switch for paralleling batteries for emergency engine start.
A VSR can be either sensed just from the engine battery or both engine or domestic battery so if you put a charger or solar onto domestic battery current will flow the other way to charge the engine battery.
A 0 volt drop splitter will have some electronics in it to turn on FET transistors so there is a potential for a failure mode with no charging at all. Compared to VSR where the engine battery circuit is totally normally connected so no failure mode of the VSR can leave you with no charge ie it charges engine battery only if VSR drops dead. A VSR is a mechanical relay while 0 volt drop splitters are all electronic. While electronics can be very reliable they still don't cope well with moisture on boards etc.
So I would go for the VSR with emergency start facility if I were you. good luck olewill

 

[pvb]

The Sterling VSR's aren't a lot cheaper than the 0 volt drop splitter which is why I was evaluating them against each other.. What other brands of VSR's could I consider that are good and reliable?

You can get a BEP 710 VSR for £45, which is good quality and will do the job.

Your question about running an inverter is a bit hypothetical, I imagine, as there's really no way you could run a 2000W inverter without significantly increasing your battery capacity.

 

[wipe_out]

Your question about running an inverter is a bit hypothetical, I imagine, as there's really no way you could run a 2000W inverter without significantly increasing your battery capacity.

Yes, it is hypothetical.. At this stage.. I am considering potentially adding an inverter and additional battery capacity in the near future for some additional creature comforts on board.. So would prefer not to have to upgrade the VSR when that happens..

Certainly seems the general consensus is towards VSR's over the electronic controllers which is positive because they are simple to wire in and obviously cheaper..

 

[halcyon]

Well if the house battery is low/flat and the engine battery is full and the engine is running so the VSR is closed and someone switches on something with a big load on the inverter it will pull the current from the engine battery and alternator through the VSR.. If the inverter is 2000W, at max load excluding inefficiency and cable losses it will pull ~167A (including cable loss and inefficiency this would be higher).. If the VSR is a 100A unit it would probably sustain a spike of 167A but at constant load it would probably burn out..

This is the scenario that current limiting VSR's protect against and splitting diodes/charge splitters don't have to worry about because the two batteries are completely isolated..

Firstly that is bad battery management, you will generate sulphation and greatly reduce battery life, keep a 50% minimum capacity for normal lead acid. Secondly it depends on VSR specification and design as to overload, also the VSR will drop out due to low voltage. You could equally say my engine battery is flat, with a VSR you can press a button and start from the service bank, a splitter will do nothing to help, just depends on what problem you look at.

With high load drop out you are not protecting the VSR, you are protecting the alternator and charge cables from high loads, or any secondary charge source fitted to the service battery, from engine starting load. It's also not new, we introduced 25 years ago.

Brian