HymerVan Posted September 22, 2017 Share Posted September 22, 2017 Earlier this year I started a thread about expected vehicle battery life in the course of which Allan from A & N Caravan services stressed the dangers of jump starting a flat battery insofar as the extremely high charging current output from newer alternators could destroy the battery. I am not challenging that advice but wondering if there is a way round it. If I understood the position correctly the battery of the restarted vehicle is still pretty flat because it is the slave battery which has done the work and consequently the vehicle battery seeks to take and the modern alternator has capacity to deliver a very high current to the battery, so high in fact that it can destroy the battery. September 2017 MMM has an article "Jump Start a Motorhome" including using Li-ion battery packs. That lead me to thinking that irrespective of how the engine is restarted the risk of "blowing" the battery is the same because the discharged condition of the vehicle battery is the same. Would it be possible to connect the Li-ion battery pack to the battery for a period of time to allow the vehicle battery to draw current sufficient to "recover" to a point where it is likely to draw less charging current and consequently reduce or eliminate the risk of post startup damage ? if so how long might that be for a typically "flat" battery. If such a procedure could work it could be done with jump leads as well but in many situations the battery pack could be connected for say an hour without difficulty whereas for traffic or other reasons doing that with jump leads might be impracticable. Link to comment Share on other sites More sharing options...
John52 Posted September 22, 2017 Share Posted September 22, 2017 If you are concerned about t he high charging current damaging the flat battery couldn't you just switch all the electrical stuff on as soon as it starts to reduce the charging current for a little while? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted September 23, 2017 Share Posted September 23, 2017 HymerVan - 2017-09-22 9:02 AM ...Would it be possible to connect the Li-ion battery pack to the battery for a period of time to allow the vehicle battery to draw current sufficient to "recover" to a point where it is likely to draw less charging current and consequently reduce or eliminate the risk of post startup damage ? if so how long might that be for a typically "flat" battery. If such a procedure could work it could be done with jump leads as well but in many situations the battery pack could be connected for say an hour without difficulty whereas for traffic or other reasons doing that with jump leads might be impracticable. Although there is plenty of information/advice on-line regarding connecting batteries together and charging the resulting combination (example here) https://www.optimabatteries.com/en-us/experience/2014/04/can-i-connect-dissimilar-batteries-parallel or regarding how best to jump-start a vehicle (example here) https://www.familyhandyman.com/automotive/car-maintenance/how-to-jumpstart-a-car-batteries-in-cars-built-after-year-2000/view-all/ I haven’t being able to find anything firm about what would occur regarding ‘current flow’ if, say, a fully-charged 100Ah 12V battery were parallel-connected to a totally-discharged 100Ah 12V battery, but no charge were then provided to the connected pair. I don’t know if the flat battery would ‘draw’ current from the fully-charged battery so that both would (simplistically) end up half-charged or (if that actually would happen) what the current transfer-speed might be. Ian Pedley’s MMM article (Pages 182 & 183 of the September 2017 issue) does not cover this and I note that, when a donor vehicle is involved, he seems to be suggesting that the donor vehicle’s motor be running when junp-starting is attempted. Conversely, advice on-line is that the donor vehicle’s ignition should not be switched on to minimise the possibility of any electrical ’surge’ affecting that vehicle. Realistically, if a vehicle’s engine won’t start due to a discharged battery, there will be an incentive to get it going ASOP. Mr AA, Mr RAC (or the Brittany Ferries guy who booster-packed a car on the last Channel crossing we took) won’t be prepared to hang about waiting for the discharged battery to slowly receive charge even if that is scientifically feasible. Having said that, it would be interesting to know if the charge of connected batteries will naturally ‘equalise’ like the water level in connected water butts. Allan can probably advise on this: if not, you might try asking MMM’s “Tech help!” team. Link to comment Share on other sites More sharing options...
John52 Posted September 23, 2017 Share Posted September 23, 2017 Derek Uzzell - 2017-09-23 8:06 AM Realistically, if a vehicle’s engine won’t start due to a discharged battery, there will be an incentive to get it going ASOP. Mr AA, Mr RAC (or the Brittany Ferries guy who booster-packed a car on the last Channel crossing we took) won’t be prepared to hang about waiting for the discharged battery to slowly receive charge even if that is scientifically feasible. . Indeed. And if another motorist has been good enough to give us a jump start we can't expect them to hang about either. So we will just have to take a chance on damaging our battery anyway. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted September 23, 2017 Share Posted September 23, 2017 Laurence’s query is a reasonable hypothetical one though. Let’s say a motorhome’s starter-battery goes flat when the vehicle is in storage and no convenient charging capability is available. If one has a jump-starting ‘booster’ and one is not pressed for time, is it a good idea to leave the booster connected to the discharged starter-battery for a while before attempting to start the motorhome’s motor? Or would that have no useful effect? Link to comment Share on other sites More sharing options...
747 Posted September 23, 2017 Share Posted September 23, 2017 As far as I understand the procedure to jump start a vehicle with a flat battery, the 'donor' needs to connect the batteries with his engine running and to leave it like that for 10 minutes or so to put a little charge into the flat battery before attempting to start the engine of the problem vehicle. Link to comment Share on other sites More sharing options...
HymerVan Posted September 23, 2017 Author Share Posted September 23, 2017 Thanks for the contributions thus far. Derek has in his last post summarised my question pretty well. Based on the advice from Allan at a and n the "normal" procedure when jump starting carries a (significant) risk that the started vehicles alternator will deliver enough current to destroy the startee vehicles battery. I don't think the mode of jump starting, be it another car, a slave battery or a jump starting battery pack makes a difference because its what happens after the startup that I was concerned about. I fully get it that breakdown service won't want to hang about to protect the old battery they will be wanting to get on to their next job and when the RAC attended my daughters almost new Nissan they jump started with a battery pack after testing her battery and saying that it was borderline. The battery failed completely the next week and Nissan replaced it under warranty. At present I carry serious heavy duty jump leads in the van and they have rescued a few other people but I have only used them on my own van once. They take significant space and payload which got me to thinking that a suitable Li-ion battery pack might work as well but not be as bulky. It may be that the answer is that there is little option but to jump start and take the risk of the alternator "frying" the battery but given Alan's advice I was exploring whether there was any way of reducing the risk. Link to comment Share on other sites More sharing options...
Cattwg Posted September 23, 2017 Share Posted September 23, 2017 Derek Uzzell - 2017-09-23 9:33 AM If one has a jump-starting ‘booster’ and one is not pressed for time, is it a good idea to leave the booster connected to the discharged starter-battery for a while before attempting to start the motorhome’s motor? This would seem a similar and reasonable scenario when two vehicles are involved. as the ‘good’ vehicle's alternator is in effect being used to charge the duff battery. From past experience (admittedly with cars) it would only take about 15 minutes to put enough juice into the duff battery to allow the good vehicle to be disconnected and for the now partially charged battery to start its own vehicle. But this poses two questions. Would connecting the good vehicle’s alternator to a duff battery pull so much current as to destroy that battery? And the original question once the problematic vehicle is started will its own alternator destroy the battery? You really have posed an interesting question HymerVan. :-D One for the experts, me thinks! Cattwg :-D Link to comment Share on other sites More sharing options...
747 Posted September 23, 2017 Share Posted September 23, 2017 Cattwg - 2017-09-23 6:16 PM Derek Uzzell - 2017-09-23 9:33 AM If one has a jump-starting ‘booster’ and one is not pressed for time, is it a good idea to leave the booster connected to the discharged starter-battery for a while before attempting to start the motorhome’s motor? This would seem a similar and reasonable scenario when two vehicles are involved. as the ‘good’ vehicle's alternator is in effect being used to charge the duff battery. From past experience (admittedly with cars) it would only take about 15 minutes to put enough juice into the duff battery to allow the good vehicle to be disconnected and for the now partially charged battery to start its own vehicle. But this poses two questions. Would connecting the good vehicle’s alternator to a duff battery pull so much current as to destroy that battery? And the original question once the problematic vehicle is started will its own alternator destroy the battery? You really have posed an interesting question HymerVan. :-D One for the experts, me thinks! Cattwg :-D You can now add something else into the mix. New alternators are classed as 'smart' and use new technology. I wonder how they perform in the case of a flat battery. Link to comment Share on other sites More sharing options...
aandncaravan Posted September 23, 2017 Share Posted September 23, 2017 Hello, Allan has asked me to point out it is much more complicated than just risk to the battery. The Alternator and Habitation electrics are a potentially much higher cost if things don't go to plan, along with damage to the donor vehicle.. See the webpage : http://www.aandncaravanservices.co.uk/jump-starting-a-motorhome.php Natalie. Link to comment Share on other sites More sharing options...
tonyishuk Posted September 24, 2017 Share Posted September 24, 2017 Reading the last post, it would seem wise to disconnect the habitation battery ( if possible) if a jump start is envisaged ? Rgds Link to comment Share on other sites More sharing options...
HymerVan Posted September 24, 2017 Author Share Posted September 24, 2017 aandncaravan - 2017-09-23 7:17 PM Hello, Allan has asked me to point out it is much more complicated than just risk to the battery. The Alternator and Habitation electrics are a potentially much higher cost if things don't go to plan, along with damage to the donor vehicle.. See the webpage : http://www.aandncaravanservices.co.uk/jump-starting-a-motorhome.php Natalie. Thanks very much for this. Actually I wondered if jump start advice would be on your "aandn" website and I did look for it but managed to have missed it. There is no ambiguity or lack of clarity in your advice so I will be making special efforts to avoid needing a jump start. Link to comment Share on other sites More sharing options...
Cattwg Posted September 24, 2017 Share Posted September 24, 2017 aandncaravan - 2017-09-23 7:17 PM Hello, Allan has asked me to point out it is much more complicated than just risk to the battery. The Alternator and Habitation electrics are a potentially much higher cost if things don't go to plan, along with damage to the donor vehicle. Natalie. Thank you Natalie. From this information, it would seem that it is not wise to play the Good Samaritan and offer to jump start someone with a flat battery – despite what your instincts may be. Many years ago I used the leisure to get out of a flat battery situation. I paralleled the batteries using jump leads. This was in the days before computer controlled engines. The ruse got me home with no apparent long term effects to either battery. However, from what has been discussed so far it would seem that this ‘solution’ may not be wise with today’s modern vehicles? Cattwg :-D Link to comment Share on other sites More sharing options...
Derek Uzzell Posted September 24, 2017 Share Posted September 24, 2017 Laurence’s inquiry was not about ‘doner vehicle’ jump-starting, but about the potential benefit of leaving a small lithium-ion booster-pack (example here) https://www.amazon.co.uk/Suaoki-Starter-Current-12000mAh-Flashlight/dp/B072FVVK1S/ref=sr_1_1?ie=UTF8&qid=1506234931&sr=8-1&keywords=suaoki+t10 connected to the vehicle-to-be-started’s battery for a period of time before attempting to start that vehicle. I have a couple of redundant elderly vehicle 12V batteries. When I checked their voltage Battery A ’s was 12.55V and Battery B’s was 12.25V. I parallel-connected them and rechecking each battery’s voltage indicated that Battery A’s voltage was slowly falling while Battery B’s voltage was slowly rising. My knowledge of electricity is similar to my knowledge of childbirth - I understand the basic principles but that’s as far as it goes - but the two batteries experiment (if it has validity) suggests that connecting a charged battery to a discharged one can raise the charge-state of the latter battery. There may be some law that could be used to decide how long it would take for two parallel-connected 12V batteries with different initial charge-states to ‘equalise’ their voltages, but I’m not aware of one. The ‘charge transfer’ during my experiment was pretty slow, suggesting that it would take a long time to bring a heavily discharged battery to a state where it might start a motorhome’s engine or risk post-start-up damage. I think Laurence’s idea is probably a non-starter (Ho Ho!) though it could be tested. The webpage referred to in Natalie’s aandncaravan posting of 23 September 2017 7:17 PM above covers realistic scenarios and best practice. Link to comment Share on other sites More sharing options...
John52 Posted September 27, 2017 Share Posted September 27, 2017 Aldi have jump leads in at the moment - looks like 25mm2 cable and 3.5m long for £9.95 The reason I mention it is because Its rare to find that quality (thickness) of cable in car jump leads Its good for diesels up to 3litre and petrol up to 5.5 litre. Link to comment Share on other sites More sharing options...
aandncaravan Posted May 31, 2018 Share Posted May 31, 2018 Had quite a few damaged Power Unit Controllers or Vehicle wiring issues following 'Jump Starts' this Spring, so may we once again advise caution? This example email about a Sargent ECxxx problem is typical. "My EC100 is showing green and charging habitation battery ok, but red and alarm when not charging the Cab battery. The starter battery was low so I jump started it, not worked right since. New battery now fitted, old one was was knack+@?d. Leisure side seems fine please advise. G". Turns out that during the Jump start, the Starter Motor had drawn power from the habitation battery burning out the in line fuse so the Sargent charger no longer had a path to the Cab battery. Not a costly fix in this case, but shows how the habitation battery can get unexpectedly involved during a jump start. See our webpage "Jump Starting a Motorhome : Why you should think twice" : http://www.aandncaravanservices.co.uk/jump-starting-a-motorhome.php Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted May 31, 2018 Share Posted May 31, 2018 So, rather than just - Don't jumpstart a motorhome- would there be any benefit in disconnecting the hab' battery (and maybe pulling a fuse or three) before the process to place?.. If there would be, then maybe there's some merit to installing hefty switches in the system?..something that would isolate the base vehicle from the caravan plonked on top? ..or is that just overly simplistic? (obviously, the above may not avoid the risk of damage to the "jump-er's" vehicle?...) If you find yourself stuck miles away from home with a flat battery,with commitments to get back for,maybe a ferry to catch etc, then rightly or wrongly, you'd need some degree of resolve to turn down a jumpstart... 8-) Link to comment Share on other sites More sharing options...
aandncaravan Posted May 31, 2018 Share Posted May 31, 2018 pepe63 - 2018-05-31 1:09 PM So, rather than just - "Don't jumpstart a motorhome" - would there be any benefit in disconnecting the hab' battery (and maybe pulling a fuse or three) before the process takes place?.. If there would be, then maybe there's some merit to installing hefty switches in the system?..something that would isolate the base vehicle from the caravan plonked on top? ..or is that just overly simplistic? (obviously, the above may not avoid the risk of damage to the "jump-er's" vehicle?...) Pepe63, Yes if you know how to 'break' the wiring from the Starter battery to the Power Controller (like maybe removing the big Red 50a fuse that is sometimes next to the Starter battery on Hymers) then it is that simplistic. Likewise installing a switch is practical if you know how. We know someone who has installed a complex switching system that switches out the habitation system and at the same time switches in a direct heavy duty cable connection between the Starter battery and the habitation battery. This enables the Habitation battery to be used as a back-up jump start source. He did this because he didn't have a great starter battery and didn't want to replace it. As a result it got worse and he relied more on the habitation battery to start the engine. Which was fine as far as it went, but he had forgotten the load on the charging systems which were working flat out continually charging up a rubbish battery that quickly discharged. First the poor 230v mains charger failed and 2 days before he was due to see us, the Alternator gave up the struggle. Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted May 31, 2018 Share Posted May 31, 2018 aandncaravan - 2018-05-31 3:27 PM Yes if you know how to 'break' the wiring from the Starter battery to the Power Controller (like maybe removing the big Red 50a fuse that is sometimes next to the Starter battery on Hymers) then it is that simplistic. Likewise installing a switch is practical if you know how. We know someone who has installed a complex switching system that switches out the habitation system and at the same time switches in a direct heavy duty cable connection between the Starter battery and the habitation battery. This enables the Habitation battery to be used as a back-up jump start source. He did this because he didn't have a great starter battery and didn't want to replace it. As a result it got worse and he relied more on the habitation battery to start the engine. Which was fine as far as it went, but he had forgotten the load on the charging systems which were working flat out continually charging up a rubbish battery that quickly discharged. First the poor 230v mains charger failed and 2 days before he was due to see us, the Alternator gave up the struggle. I suppose we all at some time or other may be guilty of holding onto a failing battery (and/or repeatedly manually recharging it, thinking that'll make it like new again) for longer than we should...but as that anecdote above shows (where presumably a new battery at the outset would've saved him a packet?) in the end- You don't get anything for nothing... ;-) Link to comment Share on other sites More sharing options...
aandncaravan Posted May 31, 2018 Share Posted May 31, 2018 Yes, replacing the Starter battery the minute it showed signs of having an issue, would have saved a lot of money. I think he paid the Dealer nearly £800, new Bosch Alternator unit, Lucas Starter battery with fitting and VAT. He still had to replace the Starter battery anyway. Because it was all so rushed, he was on his way to us and then on to the Ferry for France, he didn't get any say on the Starter battery that was fitted, which turned out to be low quality and was nearly a year old according to the dates. I wouldn't be surprised if the poor replacement battery meant he went full circle inside 3 years. So it isn't just about the jump start itself risking the habitation electrics, the web page documents the reasons why there is a risk to the Alternator following the jump start. Sometimes immediately, sometimes down the road. Unless the radio or lights have run a new battery flat, the battery has usually discharged because of an internal failing, which along with it being very dead may load up any charging system massively. The web page documents better, and cheaper (in my opinion) ways than the traditional approach of jump starting a flat battery. Link to comment Share on other sites More sharing options...
Deffheads Posted May 31, 2018 Share Posted May 31, 2018 Hi, all you Why waste time, just replace the knackered battery and fit decent solar panels or if your lucky enough to have your motorhome on the drive plug it in the mains. Maintenance free batteries are a myth [ the ones with acid in] the little green light only tells you one cell is ok, they need to be topped up, as in the good old days with distilled water every year to keep them good. Link to comment Share on other sites More sharing options...
KellyP Posted May 23, 2023 Share Posted May 23, 2023 Jump starting a vehicle with a flat battery can indeed pose risks, particularly when it comes to the high charging current output from newer alternators that could potentially damage the battery. While I am not an automotive expert, I can offer some general insights. Using a Li-ion battery pack, as mentioned in the September 2017 MMM article, may provide an alternative solution. The idea behind connecting the Li-ion battery pack to the vehicle battery for a period of time is to allow the vehicle battery to draw current and recover its charge level, reducing the risk of high charging currents damaging the battery. The length of time required for the vehicle battery to recover will depend on various factors, such as the state of discharge of the battery, its capacity, and the charging efficiency. It's difficult to provide a specific timeframe as it can vary from case to case. However, leaving the Li-ion battery pack connected for an hour, as you suggested, could potentially allow the vehicle battery to recover to a point where it draws less charging current and minimizes the risk of post-startup damage. Link to comment Share on other sites More sharing options...
simians Posted May 24, 2023 Share Posted May 24, 2023 "4 years later now 5 years later" !! My Li-ion Polymer Jumpstarter Pack instruction booklet states; 'Do not use to charge batteries, or use as a vehicle battery'. I'm not aware if this applies to all such devices. Link to comment Share on other sites More sharing options...
Basil Posted May 24, 2023 Share Posted May 24, 2023 I am not sure KellyP is correct regards using the booster pack to charge the main battery, as in the case of mine it states connect to battery terminals and then start the vehicle. In fact if you do leave connected longer than three minutes it automatically cuts off and you have to press a reset button before you can use to start the vehicle. I have to say I was very sceptical but having used it on several different vehicles it has worked perfectly on first turn of the key. Bas Link to comment Share on other sites More sharing options...
Keithl Posted May 24, 2023 Share Posted May 24, 2023 I rather got the impression that KellyP's post had the distinct style of being AI generated, especially resurrecting a five year old post! I was hoping Derek may have had an opportunity to look at his IP address as I don't have sufficient privileges to do that. Keith. Link to comment Share on other sites More sharing options...
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