ips Posted October 28, 2010 Share Posted October 28, 2010 Does anyone know at what rate my ford trannie alternator will charge the battery as in how many amps per hour sort of thing. I want to know how long it will take to charge a 85a battery and if it will keep up with something plugged into an inverter whilst driving. Pointless trying to run a 120w appliance whilst driving for an hour if the battery will be flat on arrival. Thanks in advance etc etc Link to comment Share on other sites More sharing options...
Brian Kirby Posted October 28, 2010 Share Posted October 28, 2010 I can give two part answers.First, if you have an 85Ah battery, you would be wise not to take more than about 45Ah from it before re-charging. Take more than that and you're into the injury zone. How fast that can be replaced by the alternator will, I think, depend largely on the battery itself, and how the alternator output to it is wired, and controlled. The alternator will have bags of potential power, but the battery itself can't absorb it at the same rate as it is produced.Second, an inverter running a 120W, 230V, appliance (about 0.5 Amps), will draw somewhere around 12 Amps @ 12V, so not a great deal more than your fridge. Therefore, there should still be plenty of alternator output to re-charge the leisure battery while the inverter is running. Link to comment Share on other sites More sharing options...
Clive Posted October 28, 2010 Share Posted October 28, 2010 Most light commercial vehicle alternators are rated at 90 - 100 amps. If your inverter takes less than this then the alternator will keep up with the load on the starter battery without any problems. The 120 watt appliance you quote is very similar to the headlight load. The alternator will keep the battery at close to 14 volts. C. Link to comment Share on other sites More sharing options...
ips Posted October 29, 2010 Author Share Posted October 29, 2010 Many thanks gentlemen that answers the question very well. Link to comment Share on other sites More sharing options...
djchapple Posted November 3, 2010 Share Posted November 3, 2010 I believe that the output from the alternator is controlled by a unit which senses the state of the engine battery. Thus when the engine battery is fully charged the alternator output will drop to a much lower level - even if the habitation demand is high. There are ways to modify the alternator to change this but they are not for casual DIY'ers or those worried about loss of guarantee. Link to comment Share on other sites More sharing options...
oldlowie Posted November 3, 2010 Share Posted November 3, 2010 Interesting post! What I've always wanted to know (but have been afraid to ask), is: Which is best, generator or alternator? When away from the leccy, where we find ourselves more often these days, is it best to drive around to charge the batteries (vehicle and leisure), or to fire up the genny to charge the batteries (leisure and vehicle) (?) Not too technical with the answers, please. Just a general guide would be good (lol) Link to comment Share on other sites More sharing options...
Clive Posted November 4, 2010 Share Posted November 4, 2010 dichaple is only half correct. Nearly all alternators simply provide an output of 14 volts but limited by the maximum amp capability of the alternator. C. Link to comment Share on other sites More sharing options...
ips Posted November 16, 2010 Author Share Posted November 16, 2010 well here is an update... Inverter plugged into vehicle cig lighter, travelled in the dark so lights on etc. 70miles with slow cooker on low so probably drawing about 80A ish. Worked a treat as cesserole was lovely and hot ready for us to eat as soon as we got to our destination (had been cooking all day at home so just wanted to keep it warm as no hook up on site when we got there) Trouble was that the leasure battery was only showing about 80% charge when we arrived so presumably with the vehicle lights and the inverter on the vehicle alternator was able to keep up with the usage but was not able to charge the leasure battery as well. Therefore my idea of using the inverter / slow coooker is not viable which is a shame as it worked a treat. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 16, 2010 Share Posted November 16, 2010 ips - 2010-11-16 2:22 PM .................. Therefore my idea of using the inverter / slow coooker is not viable which is a shame as it worked a treat. I assume you were also ruining your fridge on 12V? You therefore had fridge, lights, two batteries and inverter to service. I would have assumed you would have charged the leisure battery before leaving, so that would take very little extra en route. If you do it again in daylight, with the leisure battery charged on mains before you depart, it should be fine. However, you may need to beef up the wires to one or two of your circuits to get the best out of the alternator. Link to comment Share on other sites More sharing options...
ips Posted November 16, 2010 Author Share Posted November 16, 2010 Brian Yes your right I should have charged teleasure battery up 1st. Will certainly do so next time. Link to comment Share on other sites More sharing options...
Mel B Posted November 16, 2010 Share Posted November 16, 2010 Alternatively ... dump the slow cooker and get a large Thermos food flask (or two) instead .... Amazon - flask Asda - flask Link to comment Share on other sites More sharing options...
colin Posted November 16, 2010 Share Posted November 16, 2010 What temp do slow cookers work at? If you want a diy job, plumb in engine to a heat exchanger and cook food that way. Tongue firmly in cheek ;-) Link to comment Share on other sites More sharing options...
Guest Tracker Posted November 16, 2010 Share Posted November 16, 2010 If you mean charging a leisure battery you may well find the charge rate from the engine alternator is limited by the van's wiring and/or control box to about 10 amps maximum in which case it will take a lot longer to charge than the starter battery which gets the full 50 or 60 amps when low, although I understand that these days in the name of progress even this can be restricted to a lower rate. So to full charge a half discharged 85 ah battery would take in theory 4.25 hours of engine running at above tickover speed although I suspect that it would take somewhat longer due to system inefficiencies - whatever that are! If I'm wrong no doubt Brambles or another techy wizz will soon be along to tell me! Link to comment Share on other sites More sharing options...
flicka Posted November 16, 2010 Share Posted November 16, 2010 ips What wattage is your Slow Cooker (?) Our 1.5litre is only 120watt, so should only be drawing 0.5A/hr + inverter losses. For 70miles (say 1.5hours) your 80A appears high or am I missing something. :-( Link to comment Share on other sites More sharing options...
lennyhb Posted November 16, 2010 Share Posted November 16, 2010 Tracker - 2010-11-16 8:46 PM If you mean charging a leisure battery you may well find the charge rate from the engine alternator is limited by the van's wiring and/or control box to about 10 amps maximum in which case it will take a lot longer to charge than the starter battery which gets the full 50 or 60 amps when low, although I understand that these days in the name of progress even this can be restricted to a lower rate. So to full charge a half discharged 85 ah battery would take in theory 4.25 hours of engine running at above tickover speed although I suspect that it would take somewhat longer due to system inefficiencies - whatever that are! If I'm wrong no doubt Brambles or another techy wizz will soon be along to tell me! It's the battery it's self that limits the charge, most Motorhome leisure batteries are charged via simple split charge relay. When the battery is flat it's internal resistance low and it will normally charge at about 10-15 amps usually limited by the size of the wiring which causes a volt drop and the smaller the potential difference between the battery and charger the lower charge rate will be. As the battery charges the terminal voltage and internal resistance increases the charge rate drops to around 2-4 amps this usually happens after about half an hour depending on the initial battery voltage. This is why you need to drive all day to get a decent charge into the battery. Gel batteries however (information curtsey of Brambles) have a much lower internal resistance and take a much higher initial charge they appear to want to self destruct them self I've clocked mine charging at 45 amps on start up after a couple of nights away in the winter. Link to comment Share on other sites More sharing options...
ips Posted November 17, 2010 Author Share Posted November 17, 2010 flicka - 2010-11-16 9:49 PM ips What wattage is your Slow Cooker (?) Our 1.5litre is only 120watt, so should only be drawing 0.5A/hr + inverter losses. For 70miles (say 1.5hours) your 80A appears high or am I missing something. :-( Sorry just realised in previous post I stated 80A it should have read as 80W Slow cooker is 120w max so I am guessing its about 80w on low which is what we had it on. Usually on a journey like this the leasure battery is full when we arrive even if driving in the dark lights etrc on. So alternator must not have been able to cope. IMO. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 17, 2010 Share Posted November 17, 2010 flicka - 2010-11-16 9:49 PM ips What wattage is your Slow Cooker (?) Our 1.5litre is only 120watt, so should only be drawing 0.5A/hr + inverter losses. For 70miles (say 1.5hours) your 80A appears high or am I missing something. :-( You might be, John. :-) That 120W/0.5A is at 230V. However, the inverter takes 12V, so even without inverter losses, the current rises to 10A. V(12) x A(10) = W(120). Link to comment Share on other sites More sharing options...
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