pugwash Posted October 22, 2008 Share Posted October 22, 2008 Going to install a second battery in the boot to run accesories such as fridges, amps, inverters etc etc normally id just use a splitcharge to sort the charging thing but want to use this second battery to jump start the first in case of charging/starting problems- whats the best value way of doing this? Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted October 22, 2008 Share Posted October 22, 2008 Fit a normal split charge unit. Then between both +ve's of the batteries, fit a battery cut out switch (one of the red-removable key type ones is fine), so if you want to jump yerself then just turn the key. That's what i had on my 90. worked fine. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted October 22, 2008 Share Posted October 22, 2008 That Diesel Jim is what I would do. Leave the inverter out of the second battery. Fit it so that it only works with the engine runnibg. The battery will last half an hour if you are lucky with the inverter on it. Take both the pos and neg fridge wire back to the battery terminals. All the extra accessories as well. Don't use the body/chassis earth. mike Quote Link to comment Share on other sites More sharing options...
Mark Posted October 22, 2008 Share Posted October 22, 2008 As has been suggested, fit a decent split charge, and hard wire between the 2 batteries with a cut out switch in line. Alternately to Mikes suggestion (or possibly jus extending it a bit), still avoiding using the body/chassis as an earth, fit a fusebox near your 2nd battery, and wire the fridge, etc into the fuse box. Mine looks like this in the disco: Battery feeds are 16mm^2 cable as the little compressor draws a fair bit. hth Mark Quote Link to comment Share on other sites More sharing options...
zim Posted October 22, 2008 Share Posted October 22, 2008 rather than have extra cables with cut out switches, connect up another little switch to flick your split charge relay, that'll join both batteries Gordon Quote Link to comment Share on other sites More sharing options...
mmgemini Posted October 22, 2008 Share Posted October 22, 2008 Like this you mean Mark Jump leads between the two batteries. Two fuse boxes. You can just make out the second one beneath the earth leads. Yes that is a Numax battery in a Defender battery box. I made the box deeper in one part... From the right of the picture The blue relay is the Lucas SRB630 split charge relay Next is the relay for the fridge. This relay is for the Engel battery saver and voltmeter. When the voltage drops to 11.5 volt the power to the fridge is switched off. The third relay is a replacement for the GKN overdrive electronics. The fuses have now been replaced with circuit breakers. mike Quote Link to comment Share on other sites More sharing options...
western Posted October 22, 2008 Share Posted October 22, 2008 I've just done a similar internal jump start on my 110, used one of the Hella red key isolator switches & got the electricians at work to make up 2 short cables, fitted to the isolator to the front of the passenger seat box next to the winch isolator & connected each battery +ve to the isolator. it works a treat, no more digging the jumpleads out the back if I need to start the 110 with a low start battery. Quote Link to comment Share on other sites More sharing options...
MogLite Posted October 22, 2008 Share Posted October 22, 2008 Leave the inverter out of the second battery. Fit it so that it only works with the engine runnibg. The battery will last half an hour if you are lucky with the inverter on it. Thats a bit of a sweeping statement. It depends how much you are drawing through the inverter. I've got a 600W inverter, and with a minimal current draw, such as a laptop, phone charger etc. It will last a very long time before the battery gets degraded. Sure connect a 240V microwave, and its a different story. Hmmm warm pies Quote Link to comment Share on other sites More sharing options...
Superpants Posted October 22, 2008 Share Posted October 22, 2008 rather than have extra cables with cut out switches, connect up another little switch to flick your split charge relay, that'll join both batteries Gordon I'd seriously avoid doing it this way unless you have a suitably rated relay as you could potentially pull the full starting current for the vehicle through the relay, which would then overheat, or even weld contacts. You would need a relay capable of handling several hundred amps which is going to be pricey and large. The isolator switch will be rated appropriately and is likely to be a cheaper option. Quote Link to comment Share on other sites More sharing options...
Dave W Posted October 22, 2008 Share Posted October 22, 2008 You could simply use a contactor that you can control either via a switch on the dash or via the ignition or as a slave from a split charge relay if needs be. I'm going to use one of these... http://www.devon4x4.com/component/option,c...howcaticons,yes In my 3 battery setup with 2 batteries in parallel running the vehicle and winches under normal circumstances and the 3rd battery only being connected in by a voltage sensing circuit or via a switch on the dashboard (for jump start use or for when I want to use all 3 batteries for winching). The voltage sensing circuit will be the normal means of operation and the navigation PC, ignition system and Megasquirt will all run off the 3rd battery. The contactor takes under 2 amps to keep closed and is more than capable of handling the current requirements of either the starter or when winching. Quote Link to comment Share on other sites More sharing options...
Paul Humphreys Posted October 22, 2008 Share Posted October 22, 2008 I take it this is on the LC? If so I have a 3rd battery fitted in the back. The way I do it is to have the split charge to charge the 3rd battery and carry a very long set of jump leads to jump myself if needed. The reason for this is its 24v starting. Paul Quote Link to comment Share on other sites More sharing options...
zim Posted October 22, 2008 Share Posted October 22, 2008 I'd seriously avoid doing it this way unless you have a suitably rated relay as you could potentially pull the full starting current for the vehicle through the relay, which would then overheat, or even weld contacts. You would need a relay capable of handling several hundred amps which is going to be pricey and large. The isolator switch will be rated appropriately and is likely to be a cheaper option. fair enough, if your relays are 'small' then just use 2. to be honest i'm willing to bet my lunch money, that a starter will be able to turn over on a normal 100A relay. if you're going to be heating it by just turning your starter over (which is what - 3, 4, 5, 6 seconds ?), then what happens when the 2nd battery is totally flat, and it's got 60 - 100A going through it for a period of time. just my 2p Gordon Quote Link to comment Share on other sites More sharing options...
treebloke Posted October 23, 2008 Share Posted October 23, 2008 I take it this is on the LC? If so I have a 3rd battery fitted in the back. The way I do it is to have the split charge to charge the 3rd battery and carry a very long set of jump leads to jump myself if needed. The reason for this is its 24v starting.Paul If its 24v starting then surely Jim must already have two batteries?. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted October 23, 2008 Share Posted October 23, 2008 Thats a bit of a sweeping statement.It depends how much you are drawing through the inverter. I've got a 600W inverter, and with a minimal current draw, such as a laptop, phone charger etc. It will last a very long time before the battery gets degraded. Sure connect a 240V microwave, and its a different story. Hmmm warm pies I would rather do it that way then flatten my second battery then have to run the engine to recharge that battery.... It's not just the inverter. The fridge takes some and if you are running a flo light that takes a lot, A lot more than people think. mike Quote Link to comment Share on other sites More sharing options...
pugwash Posted October 23, 2008 Author Share Posted October 23, 2008 Thanks for replies guys If i go with the switched route do i need to run 2 Positive connections to the auxiliary battery- one from the split charge and one direct from the main battery I take it this is on the LC? If so I have a 3rd battery fitted in the back. The way I do it is to have the split charge to charge the 3rd battery and carry a very long set of jump leads to jump myself if needed. The reason for this is its 24v starting.Paul yep it is for the LC (didn't want to confuse the issue by mentioning 24v starting)- however i was going to use the third battery to charge the first two before i start the car- an in any case the third battery will be earthed direct to the main starting battery so i don't think it will matter if it's connected whilst the engine is being started. do i need to put in a huge fuse between the two batteries? Quote Link to comment Share on other sites More sharing options...
Mark90 Posted October 23, 2008 Share Posted October 23, 2008 If i go with the switched route do i need to run 2 Positive connections to the auxiliary battery- one from the split charge and one direct from the main battery Just run one cable and put the split charge relay across the cut-off switch terminals. do i need to put in a huge fuse between the two batteries? Either protect the cable well so avoid the possibility of shorting or use TWO big fuses, one as close to each battery as possible. As both ends of the cable are +ve both need protecting. Quote Link to comment Share on other sites More sharing options...
Ivan Posted October 23, 2008 Share Posted October 23, 2008 I have an Xeng split charge. The way it works is when the Alternator starts producing 12v through the warning light wire it connects the 2 batteries together. So all I need to do is use a switch to provide 12v to actuate the split charge relay and the batteies are connected. I can now start the car off the second battery. Or am I missing something ? Rgds Ivan Quote Link to comment Share on other sites More sharing options...
Mark Posted October 23, 2008 Share Posted October 23, 2008 Ivan, Your circuitry is correct, but when you are cranking a car you are drawing several hundred amps, and the x-eng split charge relay is only rated for 100A (I think), so you have the potential to either burn out the relay or at least weld the contacts together internally... therefore a separate line, in 35mm^2 cable with an isolator switch rated to a couple of hundred amps is a lot cheaper than a split charge relay rated similarly... In reply to Mr zimsoundz, you need to look at the sort of current being pulled by a starter motor - they draw more than you are estimating... Mark Quote Link to comment Share on other sites More sharing options...
Mark90 Posted October 23, 2008 Share Posted October 23, 2008 The X-eng split charge withstands winching, which can be similar current to starter but longer durations. Only half the current draw is going through the relay. If you where worried you could always upgrade to a 200A relay for 20-30 quid. Quote Link to comment Share on other sites More sharing options...
tacr2man Posted October 23, 2008 Share Posted October 23, 2008 I would go with what Dieseljim suggests, best bang for the buck , depending on what load you are pulling out of the inverter you need to consider what is primary and which is secondary battery. If you are parked up engine off, using lights inverter fridge then do you connect drain to first battery , and keep 2nd as reserve, or wire up all drains to second battery and leave primary battery as untouched just for start purposes? Only you can make that decision Quote Link to comment Share on other sites More sharing options...
disco_al Posted October 23, 2008 Share Posted October 23, 2008 therefore a separate line, in 35mm^2 cable with an isolator switch rated to a couple of hundred amps is a lot cheaper than a split charge relay rated similarly... if i am reading this right then, a separate line between the two batteries with an isolator switch in it - check, but, does the charge line require a separate isolator switch as well? surely once it's started, you don't want the charge voltage going straight into the second battery? Quote Link to comment Share on other sites More sharing options...
Mark Posted October 23, 2008 Share Posted October 23, 2008 In normal operation, once the vehicle is started, the charge will be going to both batteries anyway - that is the function of the split charge relay. Two batteries joined together in parallel (which is what you have once the split charge relay has clicked 'on') will attempt to even out the charge between them - that is the full one will 'charge' the flat one. When you add in the charge from the alternator, this will naturally flow to the flatter battery, as part of this process. Therefore, no, you don't need an isolator on the charge line for the 2nd battery. Mark Quote Link to comment Share on other sites More sharing options...
pugwash Posted October 23, 2008 Author Share Posted October 23, 2008 what happens to charging when you have three batteries? in an diesel LC there are 2 batteries as standard than are setup as parrallel for normal use but flick to series to produce 24v to run the starter- the alternator is 12v though- these main 2 are going to be used for not just for starting and normal 12v supply but also the main battery of the two will run the winch- I'll then add a third in the boot as a leisure battery that may or may not be charged at any time as it will be supplying the fridge, amps, inverters and in car PC. Am I going to run into any problems having 2 matched battery and an un matched third battery all linked together? The third battery will have its positives and negatives linked directly to the terminals of the main starting battery Considering the 24 stuff above what would happen if i flick the third battery to connect to the starting batteries and tehn crank the car- is there any possibilty of 24v being fed back to the third battery? If so, could this happen on starting the engine - could the split charge energise just on the starter? Quote Link to comment Share on other sites More sharing options...
Paul Humphreys Posted October 23, 2008 Share Posted October 23, 2008 As I understand the system, you are ok if you only connect to the drivers side battery. Only the passenger side turns to 24v when starting. I have my 3rd battery connected to the drivers side one via a 100amp relay. Taking the switch from the "power take off" under the bonnet, it will only charge the 3rd battery when the engine is running. Paul Quote Link to comment Share on other sites More sharing options...
steve_d Posted October 23, 2008 Share Posted October 23, 2008 Don't want to steal the thread but am confused. If during split charge the two batteries are connected together then why can I not dispense with a split charge and leave both batteries connected. I always thought you needed a split charge for a caravan because the second battery was going to be a leisure type and must be isolated from starter type currents. The application most of us are talking about here is two batteries of the same type and coping with similar currents i.e. starting or winching. As an aside I have also been told (by someone I would rate as an expert in this field) that strapping the two together is the way to go. Steve Quote Link to comment Share on other sites More sharing options...
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