dailysleaze Posted July 21, 2012 Share Posted July 21, 2012 I've been doing a lot of research and there's lots of ways of installing the RR PRC7925 expansion cap into a Defender. Difflock, EP90, AULRO all have their own versions. I'm not electronically inclined and just want something simple to solder together but these guys talk about interface modules and other magic things... The best in terms of simplicity i've found so far is from Stonefisk.com Option 1 Option 2 These seem simple enough for me, but I don't know which is better? Why does one have a transistor and a resistor, but the other has a relay, transistor and diode? One talks about preventing voltage spikes to protect the components, etc. My thought would be that having... a transistor (as a switch) a diode (preventing reverse current) a resistor (providing a route in event of coolant loss/failsafe) ...on one circuit would do the job? Any thoughts? Quote Link to comment Share on other sites More sharing options...
western Posted July 21, 2012 Share Posted July 21, 2012 I did it this way also using the PRC7925 cap/float unit & on my Td5 warning light panel, I have the water in fuel light as the low coolant warnibg, the little black box has a built in gren led, so that gives me a green all Good light & a amber low coolant light. http://forums.lr4x4.com/index.php?showtopic=49268 & the original thread with my bit on page 2 http://forum.difflock.com/viewtopic.php?t=10972&postdays=0&postorder=asc&start=30&sid=d57b4596a94f87261cd45c01158ba9ac Quote Link to comment Share on other sites More sharing options...
dailysleaze Posted July 21, 2012 Author Share Posted July 21, 2012 Cheers. I did see that one and I'm planning on using that warning lamp also. I was hoping though to try something simpler (no switches, test lights). What seems to be the key is that that solution requires an "interface module" from a guy that put them together for the difflock forum 3 years ago. I'd like to get to the bottom of what's required to make something that works like the interface module, but with component parts.. if that's possible... Quote Link to comment Share on other sites More sharing options...
TSD Posted July 21, 2012 Share Posted July 21, 2012 Don't use the one on EP90 - I didn't realise it was still publicly visible I will fix that in a minute. The circuit is correct but the relay isn't suitable. The relay acts like a tiny ignition coil... when the switch goes off, it generates a high voltage pulse which could damage the transistor. The pulse is reverse polarity to the power supplied, so the diode conducts and dumps the energy safely. Quote Link to comment Share on other sites More sharing options...
simonr Posted July 21, 2012 Share Posted July 21, 2012 Alternatively, just fit one of these in to the cap: http://www.ebay.co.uk/itm/Miniature-Float-Switch-Sensor-240Volts-Marine-Fish-Tank-/221043027440?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item337730edf0 It doesn't need any circuitry, it's just an on/off switch. Ignore the 240v - it will switch 12v just as happily. Si Quote Link to comment Share on other sites More sharing options...
mmgemini Posted July 21, 2012 Share Posted July 21, 2012 I have one that Tim from Difflock made. The second prototype actually. I used a Range Rover switch in the header tank with a level ckeck if wanted. All I can say is that it's been a fantastic bit of kit for what Tim originally charged people. Quote Link to comment Share on other sites More sharing options...
elbekko Posted July 22, 2012 Share Posted July 22, 2012 I used a switching relay, and attached an LED to the non-energized pin, so when the relay loses power due to the float dropping, the LED goes on. Not an optimal solution, but it doesn't seem to draw too much power, I had the components, and it works. I should probably hang it off the ignition someday, at the moment it's connected to the battery directly because it's right next to it. Quote Link to comment Share on other sites More sharing options...
Sirocco Posted July 22, 2012 Share Posted July 22, 2012 Don't use the one on EP90 - I didn't realise it was still publicly visible I will fix that in a minute. The circuit is correct but the relay isn't suitable. The relay acts like a tiny ignition coil... when the switch goes off, it generates a high voltage pulse which could damage the transistor. The pulse is reverse polarity to the power supplied, so the diode conducts and dumps the energy safely. glad you said that, I was going to follow that. which relay could you use? Im also looking for a solution to this. I emailed Tim regarding the interface module but never got a reply. G Quote Link to comment Share on other sites More sharing options...
western Posted July 22, 2012 Share Posted July 22, 2012 try him via http://www.teb-tec.co.uk/co/index.htm or http://forum.difflock.com/profile.php?mode=viewprofile&u=4834 Quote Link to comment Share on other sites More sharing options...
mmgemini Posted July 22, 2012 Share Posted July 22, 2012 I do have the wiring diagram for the module that Tim made. IIRC it was on Difflock originally Sorry I can't post it as my scanner is playing up. Quote Link to comment Share on other sites More sharing options...
western Posted July 22, 2012 Share Posted July 22, 2012 there's a circuit diagram in this thread for a alternative system http://forums.lr4x4.com/index.php?showtopic=15271 don't know if it's the same circuit as Mike is talking about. Quote Link to comment Share on other sites More sharing options...
TSD Posted July 22, 2012 Share Posted July 22, 2012 glad you said that, I was going to follow that. which relay could you use? Because the original LR sensor has a high resistance when switched on, you need a relay that has a high resistance coil and/or switches reliably at voltages much lower than 12V. A quick look around didn't show anything that I'm certain would work without testing - sorry. When I originally did mine, I used a relay with an electronic input similar to the second circuit dailysleaze posted above. It was left over from a bunch I made to solve a similar problem at work. If I ever get any spare time I might make a small batch (discussed it with fridgefreezer a while back) but don't hold your breath! Quote Link to comment Share on other sites More sharing options...
JimAttrill Posted July 23, 2012 Share Posted July 23, 2012 I have a float switch in the expansion tank linked to a buzzer and an LED. Quote Link to comment Share on other sites More sharing options...
Sirocco Posted August 4, 2012 Share Posted August 4, 2012 try him via http://www.teb-tec.co.uk/co/index.htm or http://forum.diffloc...wprofile&u=4834 Both emails on 'NanoControls' bounce back G Quote Link to comment Share on other sites More sharing options...
eddyoz Posted August 10, 2012 Share Posted August 10, 2012 Does anyone know of a cap similar to the PRC7925[ that fits the 300tdi expansion tank]but fits the TD5 expansion tank? Quote Link to comment Share on other sites More sharing options...
Roverdrive Posted August 18, 2012 Share Posted August 18, 2012 I just got a kit from Overlandrs which consists of the float unit, a relay, and connector block for the relay. It uses the "24v" light at the bottom right corner of the instrument panel on my 300tdi. Quote Link to comment Share on other sites More sharing options...
dailysleaze Posted September 1, 2012 Author Share Posted September 1, 2012 I've been away for the last month, but i've just bought a load of components and am going down the route of trial and error. Will report back. Quote Link to comment Share on other sites More sharing options...
western Posted September 1, 2012 Share Posted September 1, 2012 I just got a kit from Overlandrs which consists of the float unit, a relay, and connector block for the relay. It uses the "24v" light at the bottom right corner of the instrument panel on my 300tdi. do you have a link to it, the website doesn't show anything. Quote Link to comment Share on other sites More sharing options...
Sirocco Posted September 1, 2012 Share Posted September 1, 2012 stirred my interest again as I just made a list of everything I need to do before we leave the UK in January next year. The list is massive and this is another thing on the list. would like to fit a relay to ignition live but don't know if this is the right thing to do or not or which relay is best to use. G Quote Link to comment Share on other sites More sharing options...
dailysleaze Posted September 1, 2012 Author Share Posted September 1, 2012 I reckon I can get away with a transistor and a resistor to power an LED on the dash like in the Option 1 diagram in the OP. As I understand it, relays are better than transistors for larger currents and other reasons below, but I don't think it matters that much. If the circuit has to power a buzzer or something requiring more juice, then a relay might be better. It might be that the high resistance in the reed switch means not enough current passes to energise a relay. Although, it might just be swings and roundabouts. From here: http://www.kpsec.fre...om/trancirc.htm "When to use a relay Transistors cannot switch AC or high voltages (such as mains electricity) and they are not usually a good choice for switching large currents (> 5A). In these cases a relay will be needed, but note that a low power transistor may still be needed to switch the current for the relay's coil! Advantages of relays: Relays can switch AC and DC, transistors can only switch DC. Relays can switch high voltages, transistors cannot. Relays are a better choice for switching large currents (> 5A). Relays can switch many contacts at once. Disadvantages of relays: Relays are bulkier than transistors for switching small currents. Relays cannot switch rapidly, transistors can switch many times per second. Relays use more power due to the current flowing through their coil. Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil." Quote Link to comment Share on other sites More sharing options...
Roverdrive Posted September 1, 2012 Share Posted September 1, 2012 Western I just called in to his shop, and he mentioned it, so I bought one. Not been on the web site, so I can't comment. I think the relay is a Durlite unit with NC contacts. Dailysleeze The relay option seems to be working ok for me. Nice and simple, and the reed switch can operate the relay's coil. Quote Link to comment Share on other sites More sharing options...
western Posted September 1, 2012 Share Posted September 1, 2012 Thanks for the info, on mine I used the 'water in fuel' amber warning light as my low coolant warning, the little black interface box from ten-tec has a built in green led, so I have a good level & do something about it warning lights, [my instrument pack is a Td5 unit] Quote Link to comment Share on other sites More sharing options...
dailysleaze Posted September 20, 2012 Author Share Posted September 20, 2012 Woo it works! I went for option 2 in the OP, albeit I want to use the "Water in filter" warning light on the Td5 dash, which requires a switched earth, so I changed the relay to switch earth rather than ignition. High coolant, switch is closed and relay energised, holding contacts away from warning light Low coolant, switch is open and relay not energised, so contacts default to connecting the warning light Break in the wire to the sensor, therefore relay not energised and failing safe The PCB board came with a little black box, so I can house it behind the dash or somewhere When the ignition goes on, there is a brief flash of the light as the relay energises I'm so chuffed as i've never attempted anything electronic, but it worked first time!! All the credit really goes to that diagram on Stonefish. I just adapted it slightly to suit my requirements. Vehicle installation soon! Quote Link to comment Share on other sites More sharing options...
elbekko Posted September 21, 2012 Share Posted September 21, 2012 The relay still works fine for me too, still connected to permanent + because I'm too lazy to change it. I've left the car standing for a few days without starting problems, so I'm confident it isn't drawing too much power. I just zip-tied the relay to the bracket holding the coolant tank, and ran a cable to the dash to a 12V LED that's grounded there. The only pain is unscrewing the coolant cap, you have to hold the centre part of the cap so you don't force the cables too much. Quote Link to comment Share on other sites More sharing options...
Sirocco Posted December 22, 2012 Share Posted December 22, 2012 How is the home made box holding up Dailysleaze? Been a few months of testing Which relay did you use Elbekko? Was it a low draw one? G Quote Link to comment Share on other sites More sharing options...
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