JetSepter Posted May 30, 2011 Share Posted May 30, 2011 parasitic load." This point is made a few times on the forum, but how does it translate into effect on the battery? Does it mean a gel battery with a parasitic load - a load which all Sevens with immobilisers have - will last for only 10 -20-30 - etc % of its normal service life? Or is battery performance affected in some other way? Will some expert please shine the light for this numpty? Link to comment Share on other sites More sharing options...
Team Escargot Posted May 30, 2011 Share Posted May 30, 2011 I am no expert - I was advised that gel batteries do not like trickle loads such as with an immobiliser; however, my redtop is in its 5th year - I have an immobiliser but also a battery cut off switch. Nick Link to comment Share on other sites More sharing options...
6speedmanual Posted May 30, 2011 Share Posted May 30, 2011 I understand that if they get fully discharged it is impssible to bring them back up. If isolated they can hold charge for ages. My classic car has one and left standing in a cold dry barn it started first time, cranking enthusiastically after 15 months of inattention. Isolater is the way to go as it isolates battery from you immobiliser too. Peter Link to comment Share on other sites More sharing options...
DJ. Posted May 30, 2011 Share Posted May 30, 2011 It only takes 2 minutes to disconnect the negative lead from the battery. At least with a Seven, there's no clock or radio to reset Duncan Link to comment Share on other sites More sharing options...
michaeljclark Posted May 30, 2011 Share Posted May 30, 2011 Quoting DJ.: It only takes 2 minutes to disconnect the negative lead from the battery. This is true, however I found that this became a faff after a month or two - bonnet off, secure bonnet, spanners out, do the work, spanners away, bonnet back on, etc etc Master switch is the answer!! Mike Link to comment Share on other sites More sharing options...
JetSepter Posted May 30, 2011 Author Share Posted May 30, 2011 So do I gather the rationale is basically that gel batteries can't be resuscitated if they are allowed to go flat, and that this is more likely to happen if there is a parasitic load? Would make sense. Some insurance policies require the car to have an immobiliser, and I wondered how fitting a cut-off switch would affect that. I guess the answer is that a) the switch is itself an immobiliser, albeit not approved as such, and b) anyone connecting the battery will in fact switch on the immobiliser again, so the requirement continues to be met. Link to comment Share on other sites More sharing options...
Sheds Moderator Posted May 31, 2011 Share Posted May 31, 2011 I'd go along with your take on the immobiliser. Let's be honest, if you fit one and the car is still stolen, nobody is in a position to worry about a battery isolator because, er, the car was stolen. If it turns up post theft, well and good. It's got a BMS? Yes it has. All you need is the isolator receipt. My view on parasitic load is that it is *likely* to be related to duty cycles in batteries of different design. A truck battery will deliver massive current for a few seconds (starting) but then be topped up all day. If however you try to run (say) the headlamps all day it won't like it and will go flat fairly quickly. Do this regularly and there is a greaterr chance of the thing failing in service. A leisure (caravan, boat) battery will run headlamps all day every day and not care, it is designed as a deep cycle battery and that's what it does. Ask it to start a truck though and it will fail very quickly. I suspect that a gel battery is more like the truck battery above - it's there to start the engine, but if you leave a small load on it it will go flat quicker than you'd think and have a greater chance of packing up. You can of course fix this with a small charger/batt conditioner if your garage has power. Link to comment Share on other sites More sharing options...
JetSepter Posted May 31, 2011 Author Share Posted May 31, 2011 BOSS - so a 30ampere-hour battery is not exactly a 30Ah battery, in that its capacity depends what sort of amps (eg starting, headlamp or parasitic ) you are pulling out of it at any one time? I can see that a battery might be constructed in a way that meant it couldn't stand up to a hefty starting current for very long, but I find the opposite idea difficult to get my head round. Can someone versed in these things explain the basic (and I mean basic!) chemistry to me? Douglas Link to comment Share on other sites More sharing options...
Pete-B Posted May 31, 2011 Share Posted May 31, 2011 Having got a Powervamp I've obviously got the same problems with parasitic loads but being a complete dumbo where car electrics are concerned theres no way I'm going to let myself loose on the wiring by trying to fit a battery master switch. Someone in search suggested the easy way is to use a quick fit battery cut out switch - Amazon do them for few pounds - but they all seem to come with post fitting, so how does one get over that with Powervamp screw type fitting? Link to comment Share on other sites More sharing options...
Sheds Moderator Posted May 31, 2011 Share Posted May 31, 2011 Quoting JetSepter: BOSS - so a 30ampere-hour battery is not exactly a 30Ah battery, in that its capacity depends what sort of amps (eg starting, headlamp or parasitic ) you are pulling out of it at any one time? Can someone versed in these things explain the basic (and I mean basic!) chemistry to me? Douglas Yes, that's definitely the case. A 30 Ah battery will deliver 1A for 30 hrs, 2A for 15, but connect a 30A load and it will be flat in under an hour. This is derating under high current load and is standard. In terms of the chemistry I suppose that at heavy discharge the chemical reactions just can't keep up; the local concentrations where the acid hits the lead plates decline to the point at which the reactions no longer happen. In terms of "don't like" don't confuse "unable to do" with "elevated failure rate". In other words, if you try to start a truck with a caravan deep cycle battery it probably won't work at all. From the start it will not deliver the hundreds of amps required. Conversely if you take the truck battery it will work in a caravan, for a while. Over time though I would expect it to "sulphate up" where the sulphuric acid and lead react to produce insoluble lead sulphate. This reaction will stop the battery working *in the long term* - it may lose its charge, it may develop a high internal resistance, or whatever, but you will see an elevated failure rate in service. I suspect that this is what we are looking at with the gel batteries - they will work but you'll probably see them failing more often after a year, 2 years, however long, when those NOT connected to a parasitic load generally go on in service for many years. In terms of chemistry and explanations in a gel battery, I don't know. Link to comment Share on other sites More sharing options...
JetSepter Posted May 31, 2011 Author Share Posted May 31, 2011 Thanks BOSS Link to comment Share on other sites More sharing options...
Ian B Posted May 31, 2011 Share Posted May 31, 2011 they all seem to come with post fitting, so how does one get over that with Powervamp screw type fitting? Pete, you can use one of these here - as it happens I might have a new pair I bought and don't need, and if I can find them you can have them for a tenner plus postage Doug, just fit a battery isolator and drive the thing Link to comment Share on other sites More sharing options...
JetSepter Posted May 31, 2011 Author Share Posted May 31, 2011 You're right of course, Ian, I'm doing too much chattin' and not enough blattin' 😬 But I'm learning quite a lot from you erudite gentlemen Link to comment Share on other sites More sharing options...
Myles Posted May 31, 2011 Share Posted May 31, 2011 Somewhere, I've got some of the tech literature from Powervamp. From memory, the life of a 'red top' battery is quoted in terms of the depth of discharge and the number of cycles. It goes from the dramatic on a total-loss racecar with no alternator and a deep discharge to lots-and-lots of cycles if just discharged a couple of percent. Ah! Found it. Discharge by 10% of capacity - allows battery to be cycled c. 2000 times. Discharge to 80% of capacity - reduced number of cycles to c. 200 Link to comment Share on other sites More sharing options...
JetSepter Posted May 31, 2011 Author Share Posted May 31, 2011 Hah! Got the point. Ta Link to comment Share on other sites More sharing options...
Roger Ford Posted June 1, 2011 Share Posted June 1, 2011 Ah! Found it. Discharge by 10% of capacity - allows battery to be cycled c. 2000 times. Discharge to 80% of capacity - reduced number of cycles to c. 200 You've got "by" in one of those, and "to" in the other - should the second one read "discharge by 80% of capacity"? If so, it's not as much of a difference as it may sound - if it was a 20AH battery, then the total power drawn would be 2000 x 2 = 4000 AH in the first case, and 200 x 16 = 3200AH in the second. Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 1, 2011 Share Posted June 1, 2011 Well, yes it is a huge difference, because you aren't using the battery as fuel. It's a rechargeable battery so the energy is replaced by the alternator/engine. The amount of energy required per trip is neither here nor there. The key to it really is the number of cycles - let's say I use my car 6 days a week, 4 journeys a day, that's 24 cycles a week or 1200 a year. The battery used optimally will last almost 2 years, the abused one will be dead after 2 months. I'm not going to tolerate having a car that won't start every 2 months. Link to comment Share on other sites More sharing options...
Myles Posted June 1, 2011 Share Posted June 1, 2011 You've got "by" in one of those, and "to" in the other Good catch - I'll check tonight - but am pretty-sure it should be 'by 10%' and 'by 80%' in both cases. Link to comment Share on other sites More sharing options...
Roger Ford Posted June 1, 2011 Share Posted June 1, 2011 Well, yes it is a huge difference, because you aren't using the battery as fuel. It's a rechargeable battery so the energy is replaced by the alternator/engine. The amount of energy required per trip is neither here nor there. The key to it really is the number of cycles So how would you "discharge by 80%" if it was being topped up by the alternator? The very use of the language implies that you ARE using the battery as fuel - perhaps to run an immobiliser or other static load. If you're using it just to start the car and then immediately recharging it I can't see how you'd use 10%, let alone 80%, so I can't see where your "abused" scenario would come from. Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 2, 2011 Share Posted June 2, 2011 They are hypothetical situations, the question is about what is meant by "gel batteries don't like..." and why, and what the failure modes are. The point I'm making is that the number of joules or Ah delivered by the barrery isn't very important compared to the number of cycles it will go through, from the POV of the user of the car. I don't know what energy is used or what Ah are required to start my car, and I don't really care. If however it fails to start because it won't do that many duty cycles then I know all about it, and you bet I care. Link to comment Share on other sites More sharing options...
Pete-B Posted June 2, 2011 Share Posted June 2, 2011 I've just received this from Eward Roller who's the tech man at Powervamp;- Could I suggest that you add to the existing thread on the forum stating that you have spoken to myself and I have agreed that you can cut and paste the following… “The Powervamp range of racing batteries have different characteristics to a conventional ‘wet’ battery, and these need to be catered for to maximum your batteries longevity. The PVR batteries are of a much lower amp/hour capacity, which basically means that any load or drain on the battery whilst the engine is switched off, (ie. the alternator is not putting power back into the battery), will flatten it more quickly, which can lead to, if undetected, a ‘deep discharge failure which is unrecoverable. The fitting of a ‘kill’ switch in the positive line to the battery will isolate the battery when not in use and also act as an immobiliser once the key has been removed. This relatively inexpensive modification could save you the cost of a new battery and is recommended where at all possible.” Obviously, if you or any of the other forum members wish to ask any further questions I would be only too happy to answer them. Link to comment Share on other sites More sharing options...
Neil_K Posted June 3, 2011 Share Posted June 3, 2011 I did deep discharge mine by accident about 3 years ago and it did recover after a week on life support (7 stage charger) to hold 12.8V across the terminals. Given that it is now 4 years old, it STILL holds 12.8V without further degredation and so far has had no starting issues. I accept that I probably damaged it by a certain degree 3 years ago and obviously don't suggest leaving a load on the battery, but now I do not disconnect the immobiliser and simply plug a trickle charger into a port (few quid from ebay) secured under the ECU. Simply unclip the 1 bonnet latch by the ECO and lift enough to clip in/clip out the charger Link to comment Share on other sites More sharing options...
Richard J Darnell Posted June 3, 2011 Share Posted June 3, 2011 I've just fitted a powevamp PVR25 to my 1.6k and also bought a powervamp charger (the cheapest they do) The website says I can leave the charger pugged in indefinitely wihout risk of over charging. I plug my car in after every blat (via the power scoket I fitted) and set the immobiliser. Will this deal with the parasitic load issue or should I fit a kill switch? (Incidentally, the PVR25 turns the engine over faster than any Banner battery has done in the past so very pleased so far......but will it last) Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 3, 2011 Share Posted June 3, 2011 The charger will deal with the load from the immobiliser no probs. The cheapest charger anywhere will deliver 500mA, immobilisers need maybe 50 or 100. The balance of payments is still positive. Link to comment Share on other sites More sharing options...
Richard J Darnell Posted June 3, 2011 Share Posted June 3, 2011 Cheers BOSS, that's what I thought (the charger delievers 650mA) It's been a long time since I've post on blatchat but good to see lots of familiar names! Link to comment Share on other sites More sharing options...
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