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Voltage Sensitive Relay (VSR) and 5v / 19v charger advice and comments


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Two smallish batteries, start and house.  Isolator switch is fitted that allows either or both batteries to power the starter.

Machine sensed Ingrams Bosch pattern alternator - I'm assuming 55A.

120w solar panel.

Normal loads for a low-specced 10m yacht - cabin and nav lighting, vhf, stereo, fridge, pi-plotter and screen, occasional charging of cell phones and laptop.

I'm thinking this is sufficient for a VSR - any comments?

Also, the existing laptop and cellphone charging devices cause a lot of interference on VHF and FM radio signals.  The radios share a masthead antenna through a splitter.  Any solutions to this interference out there?

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That looks very cheap..... I would tend to go for a Blue Seas Marine version which works superbly on my 10M keeler doing all the same stuff, (no connection to Lustys who sell them) 

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I like to take a slightly different approach. The VSR basically turns your 2 batteries into 1 and effectively limits the charge going into the house battery (because the starting batt will be at a higher level of charge), which is the one that will require more charge.

So I would use one of these, buy from Defender in USA

https://balmar.net/products/digital-duo-charge/

Ideally you want an external regulator for the alternator (if it can receive and external field signal).

If you want to look at an upgrade I have a pair of 6 V 220 ahr hybrid gel batteries (used but still in good nick) plus an 80 amp externally controlled alternator (reconditioned) available at a very good price  - PM me if you are interested

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3 minutes ago, marinheiro said:

If you want to look at an upgrade I have a pair of 6 V 220 ahr hybrid gel batteries (used but still in good nick) plus an 80 amp externally controlled alternator (reconditioned) available at a very good price  - PM me if you are interested

Thanks MH, but I suspect that would seriously overcapitalise our yacht. 

The charge control device is interesting tech though - thanks for the link. 

We don't have any real problem with capacity atm, but I would like to take the "human cock-up factor" out of the charging network which is manually controlled by the isolator switch currently.

I did my time as an auto-electrician, so I can turn the alternator thats fitted into any configuration (int/ext regulated, machine/battery sensed etc) without too much trouble.  I was going to put a diode splitter into the battery system and lift the alternator output voltage to match it by putting a diode in the machine sensing circuit, but a VSR just seems a simpler and better solution.

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I use a VSR, its cheap, simple and perfectly useful for an unsophisticated system. To keep the batteries on a float charge I use a small regulated solar panel. Suggest downloading the documentation from BEP for a read, but there are many, many models out there. If I had an expensive system then I would be doing a lot more research, but I have used the BEP model for 15 years without a problem.

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Keep it simple. Simplest is to not worry about the VSR. Use a charge splitter to divide the charge to which battery needs charge. This ensures your batteries will always get a trickle charge when the boat is not in use and Banks are full. It also means that two batteries that are at different charge capacities do not unbalance the draw of current and one gets all and the other very little. VSR's were designed for a small power boat situation where it was about having a spare start battery and ensuring at least one battery was left with enough charge to start the motor, incase the Radio was on full bore for a long time.

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Use a FET based splitter. Then no need to change the voltage as needed with a diode based one. The victron Argo FET based ones have a voltage drop of <0.02v.

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IT can you explain the practical difference, as Wheels said I always thought the VSR filled one battery up then the second so all is well. Which is what I wanted on my uber basic system. Mainly it was so that I could always start the engine, never really considered the downsides. A friend in the marina just spent 6k on a lithium setup as a contrast- and  that is a whole different scenario to me wandering into Burnso and pointing to "that one please" because it looks about right  :) 

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Firstly, the FET one IT has suggested has 0V loss, so you get full charge voltage to banks,
There are two ways of connecting a VSR. Either a Disconnect and a Voltage threshold so as the Start bank is never fully drained. Or as you said, charge one, then the other. However, in either situation, the second is switched back in at an unequal charge state compared to the other. Thus even identicle batteries will present different charge loads. The Battery presenting the greater load hogs all the current. You would expect that the batteries would even out, but that is not often the case. So one ends up hogging the load and ends up over charging. The one presenting the least load never gets to a full charge. This is not an issue for say a trailer boat and you can put a charger on it at home. But for a boat out on a mooring, the problem compounds till eventually one battery, or maybe both, fail prematurely.
While that VSR is cheap, if compared to a good make, they are similar prices to a FET splitter, so I would be going down that path rather than the VSR.

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My Batteries are switched off when I leave the boat but small solar is wired to the house one (through mppt charger) and happily as it turns out also feeds the start battery through the VSR , I had not realised that it could work both ways. Have not had to plug in for five years.

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Some models of vsr sense voltage in both batts, and will engage when either batt reaches the setpoint. Then disengage when both batts drop below the cut out point. Be aware that if you make one bank real flat, the vsr may not work at all, as most require at least 10.5v on the least charged batt, or they won't engage....

A sensor to detect alt output, and to engage both batts at that point is not advisable, unless it can be manually overridden. If you cook a bank, you need  to be able to disengage it. Every batt bank should have an off switch,  and it should be all batt connections, including the alternator. Batt fuses are a good idea as well.

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