 | Home > Technical > Which Voltage Sensing Relay |
 
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324  
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I bought a generic 140amp one and it performs perfectly:
 Click image to enlarge Darren 110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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12th Sep 2019 4:07pm |
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| Bluest Member Since: 23 Apr 2016 Location: Lancashire Posts: 4216 
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You need to decide if you want the ability to combine batteries for a self jump start scenario. I think the Victron and T Maxx ones let you do that. If not, the generic Durite/M-Power 140 amp ones do the job ok. I think mine is an M Power one from Simply Split Charge. 2007 110 TDCi Station Wagon XS
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12th Sep 2019 4:26pm |
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| kmac Member Since: 07 Oct 2009 Location: Middlesex Posts: 1309 
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Thanks both - will give it some more thought and decide based on price and availability
Touch wood I have not had to jump start the vehicle ever so maybe that's less of an issue. One can always manually disconnect the VSR when doing so I guess. |
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13th Sep 2019 9:24am |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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Yes, you can. The thin black wire in my photo above is the trigger wire, which just needs to be earthed. In its' simplest form, it can be connected to the battery neg terminal but by routing it through a switch you can create a manual override to disable the VSR. Darren
110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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13th Sep 2019 9:32am |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20446
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I would go with Durite.
Whilst a VSR is good for split charge battery set ups. I’d be cautious on use for other more sensitive electronic equipment purposes, as there is a cut in voltage and cut off voltage. On start up the Defender by nature always has a significant voltage drop often circa 8 - 9v during cranking. So ignition would trigger it, cranking drop it off and then when motor is running it’ll be back on again. Often in a pretty sudden and extreme manner. For purposes other than split charging etc I’d rather use a traditional relay as the coil voltage drop out of the switch disconnection is typically lower. They are also significantly cheaper, easy to change and pretty reliable. (Fining a RMT 12v ignition switched source to trigger is usually not a problem at all either.) Either way, BlueSea and Durite you won’t go wrong with.  No Guts, No Glory.
🇬🇧🏴🏴🏴🇮🇪🇺🇸⛽️🛢️⚙️🧰💪 |
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13th Sep 2019 10:43am |
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| kmac Member Since: 07 Oct 2009 Location: Middlesex Posts: 1309
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Thanks Steve - this is for split charge only.
You mention Blue Sea and Durite - latter is a simple VSR rated to 140amps and costs about 40 quid. Former costs a lot more, main one sold via kits form the likes of Mobile centre is rated at 500Amps continuous and costs almost 300 quid |
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13th Sep 2019 11:50am |
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| TJH1985 Member Since: 22 Aug 2016 Location: Midlands Posts: 238
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I have the 180 amp CARGO (Bosch) and have no complaints
Comes in at 13.4volts and switch off at 12.6volts so doesn't cut in until a few (ish) seconds after the engine is running. I have have a secondary fused link that I can connect to bypass it, for if I ever need to jumpstart. I use it to run a fridge, charge phones, CB etc |
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13th Sep 2019 11:58am |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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That's not the way these VSR's work. The cut in voltage is such that they don't connect until the engine is started and stable, so they don't cut in and out during starting. They're also solid state, so no coil and associated EMI. There's no problem using these in circuit with electronics. Darren 110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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13th Sep 2019 12:52pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1223  
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Not true - just likely to be less intrusive and more easily dealt with by the filters in the electronic power supplies. Ed 82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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13th Sep 2019 2:30pm |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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Not true about the coil or the EMI, or both?
 Darren
110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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13th Sep 2019 2:58pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1223
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Both and/or one or the other...
Clue is in the name. Voltage sensitive/sensing relay. Normally they'd make a song and dance about it being a solid state relay VSSSR  .
For applications like this it makes more sense to use a good old fashioned relay because once closed realistically it's resistance is effectively 0 ohms. Even the best high current MOSFETs will have an Rds(on) (on state resistance) of a few milliohms which means they'll heat up and you need to get shot of that. At high currents it adds up quickly (in fact squares) so unless you need high speeds then there's no point. You will also get EMI issues with solid state stuff, in fact in most scenarios (this not being one) its worst. The problem is in the switching, all wiring has inductance which is an opposition to changing current. You in effect build up charge in the cable which then causes an overshoot of the voltage. It's a right sod to deal with and the low frequency stuff unfortunately just means bigger components which means more money which is where cost is usually cut on cheaper electronics. You can create a much cheaper VSR by simply wiring a relay up to the W (or is it Y) terminal on the alternator. Once the alternator is turning (and in most scenarios the engine is running) then that voltage is no longer shorted to ground and rises to battery which can be used to only turn on the relay when the engine is running. I had this but with an extra switch in parallel to a permanent live so I could connect both batteries if I wanted when the engine was off. However, most VSRs are a bit more intelligent in that they monitor the voltage and can guess at when the primary battery is charged before switching in the second. There is a good discussion on a thread involving Si Rafferty on LR4x4 where the idea behind the X-Charge came to fruition which details the pros and cons of each method. Ed 82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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13th Sep 2019 3:18pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1223
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The best of both worlds would be a microcontroller driving a relay. You could also use something called an ideal diode (built using MOSFETs) which allows you to actually control charge direction should you so desire. Ed
82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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13th Sep 2019 3:21pm |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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Ah, ok. Interesting. I'd always assumed they were solid state given the way that the operate and that the term 'relay' was being used figuratively. I'm happy to stand corrected though. I guess the relevant point is that they don't suffer from the issues that Steve suggested above, of the voltage dropping in and out on starting and being aggressive to electronics.
I've done exactly this in the past, fitted to a 300tdi Discovery. It used, from memory, a 180amp relay as the base and included a manual override switch (and some LED's to indicate what it was doing). I used it to charge two 100amp batteries in a trailer and it was very effective. The modern VSR's are just easier to install and, as you mention, include some nice monitoring features. Darren 110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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13th Sep 2019 3:38pm |
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| Mo Murphy Member Since: 01 Jun 2008 Location: Letchworth Garden City, Herts Posts: 2244 
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I just use a 100 amp relay switched by the alternator. If I need to jump start myself, which I've only ever needed to do once, I plug the jump leads into the Anderson connector and onto the leisure battery and then leave for 30 minutes.
I run the fridge, scenelites and charging points off the leisure battery and has served me well on many trips abroad. It's not fancy or elegant or trick but it is inexpensive and simple 
Mo The Land Rover 90 - Many are called, few are chosen. 50 Shades of Pennine Grey |
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13th Sep 2019 4:15pm |
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