Lotus Elan

Power Bank

PostPost by: KevJ+2 » Thu Jul 13, 2017 1:19 pm

Just saw this and thought what a handy pocket sized backup it is!
http://www.ebay.co.uk/itm/Silverline-42 ... 3025612710
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PostPost by: mbell » Thu Jul 13, 2017 6:05 pm

I have a similar device, works very well.

I actually mostly use it for running my 12v car lift! Normally have to break it out if I've not run the car in few weeks (need to check/clean few connections). It goes months of use between recharges. I have no doubt it would make light work of start pretty much any passenger vehicle engine, yet to try it only my daily but sure it would start the 4.4 V8 easily.

They come in various sizes but are multi-function as can be jump starts, torch, USB charger, laptop power supply. So useful thing to have around not just for starting the car with out need heavy jump start unit.
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PostPost by: billwill » Thu Jul 13, 2017 10:57 pm

I've been trying to follow adverts for similar devices for emergency car starting, but they don't seem to make sense, the adverts don't mention how to recharge its lithium battery.

?
:?:
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PostPost by: mbell » Thu Jul 13, 2017 11:43 pm

They normally come with a wall charger and car 12v plug. You just plug them in and leave for a long time...
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PostPost by: mbell » Thu Jul 13, 2017 11:46 pm

They store a lot of energy thou so youwant to make sure to get a decent quality one and not a fake. They can be very dangerous.
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PostPost by: elanfan1 » Fri Jul 14, 2017 12:02 am

It will become apparent very soon that I haven't got a Scooby do but... How can such a small device with thin cables possibly power a flat battery to enable a jump start? I had cheapo jump cables back in the day that were thin and all that would happen is they'd get hot and not do anything at all. I bought some proper thick ones and all was well.
Further how does a power pack rated at 6000 milliamphours possibly produce enough power for a car emergency start - the advert is claiming 400ah output - where does this come from? Is it magic? My kids have similarly rated back up chargers for their phones which buy them a few more hours of phone usage I fail to understand this stuff.

Is this all puff or is there some truth in it? Apologies in advance.
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PostPost by: pharriso » Fri Jul 14, 2017 12:07 am

elanfan1 wrote:Further how does a power pack rated at 6000 milliamphours possibly produce enough power for a car emergency start - the advert is claiming 400ah output - where does this come from? Is it magic? My kids have similarly rated back up chargers for their phones which buy them a few more hours of phone usage I fail to understand this stuff.

Is this all puff or is there some truth in it? Apologies in advance.


Enquiring minds need to know! :P
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PostPost by: elanfan1 » Fri Jul 14, 2017 12:10 am

My mind is like a sieve - I blame it on having had a cerebral fluid leak for 5 months!

Educate me!
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PostPost by: Chancer » Fri Jul 14, 2017 8:21 am

You are not alone in your scepticism regarding the cables, the AH capacity and the claimed 400 amps.

The cable length is short so voltage drop will be reduced, having seen the videos of Li-ion batteries self destructing then clearly high currents are possible but for a very short period of time with such a small capacity.

The predecessors of these things were the charging stations with tyre inflators containing sealed lead acid gel batteries, my experience with them were they were crap compared to my proper charge-starter which would crank a vehicle with a dead battery, the charge starter was like using a moped battery and bell wire to jump start.
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PostPost by: nmauduit » Fri Jul 14, 2017 8:26 am

elanfan1 wrote:Further how does a power pack rated at 6000 milliamphours possibly produce enough power for a car emergency start - the advert is claiming 400ah output - where does this come from? Is it magic? My kids have similarly rated back up chargers for their phones which buy them a few more hours of phone usage I fail to understand this stuff.

Is this all puff or is there some truth in it? Apologies in advance.


if it works as advertised, you do the math and make sure you start your engine quickly, as if nothing melts it will be flat in less than one minute...

No magic there, I have a similar type battery in my S4, except that it is 36Ah (motorcycle battery), rated a bit more actually (540A peak) - it can last a few minutes, but the cables do get hot after one, and that is not an exercise you want to prolong much in any case for the sake of the battery.
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PostPost by: ericbushby » Fri Jul 14, 2017 9:23 am

Phil and Steve,
A 400 amphour battery will give 400 amps for 1 hour, or 1 amp for 400 hours.
The maximum current available depends on its internal construction.
This is a 6 amphour battery so it will give 400amps for 6/400 - 0.015 hours or 54 seconds as suggested by nmaudit above.
If we allow for 50 percent losses due to small cables, internal resistance in the battery etcetera we now get 27 seconds.
My car takes 160 amps to start it so it will last for 67.5 seconds, whlch, if there is no problem except a flat battery should be enough to start it.
I hope this explains it and please notice that I have not said this is a good idea.
I think some small jump leads to re-charge you car battery for a few minutes from your new friends car is more likely to work and you are not carrying a high energy lithium battery.
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Last edited by ericbushby on Fri Jul 14, 2017 10:56 am, edited 1 time in total.
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PostPost by: rgh0 » Fri Jul 14, 2017 10:01 am

New cars thanks to gear reduction starters and lower viscosity modern synthetic oils and better tolerance machining producing lower internal friction need a much lower peak starting current. They also start quickly and easily due to modern electronic ignition and fuel injection.Due to all the electrics though they have a much higher running electric power demand. The cable from the battery to the starter on my Landcruiser is no bigger than the cable from the alternator.

A 200+ amp / 6 amp hour Lithium ion battery that can put out that current for a minute or so is plenty to start modern cars.

It may struggle with an aging original Lucas starter in a tight Elan engine with dino oil on a cold day when it needs to crank for a minute just to get fuel to the carbs :roll:

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PostPost by: denicholls2 » Fri Jul 14, 2017 2:05 pm

mbell wrote:They can be very dangerous.


Yes. While this might be OK for plugging in and adding to a battery that has discharged by, for example, leaving the lights on, it is scary in the use posters are referring to of a hot jump.

Lithium Ion batteries have a very high discharge rate, which permits them to deliver a lot of current all at once provided the conductors to deliver it are present (hence the 400 amp rating). But they are notoriously intolerant of charge rates outside of their design parameters (anyone ever heard of flaming Galaxy phones or hoverboards?) While the quality of the batteries is a big contributor in these events, physics does not like to be denied. :shock:

A hot jump isn't problematic on the starting side of the process, but disconnection needs to be immediate. The current flowing back to the battery when the engine starts is almost certainly going to be way above design parameters and a prime opportunity for a battery explosion. I wouldn't want to melt an Elan that way.

Yes, you could implement a protection circuit to prevent reverse flow.
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PostPost by: nmauduit » Fri Jul 14, 2017 2:32 pm

denicholls2 wrote:
mbell wrote:They can be very dangerous.


Yes. While this might be OK for plugging in and adding to a battery that has discharged by, for example, leaving the lights on, it is scary in the use posters are referring to of a hot jump.

Lithium Ion batteries have a very high discharge rate, which permits them to deliver a lot of current all at once provided the conductors to deliver it are present (hence the 400 amp rating). But they are notoriously intolerant of charge rates outside of their design parameters (anyone ever heard of flaming Galaxy phones or hoverboards?) While the quality of the batteries is a big contributor in these events, physics does not like to be denied. :shock:

A hot jump isn't problematic on the starting side of the process, but disconnection needs to be immediate. The current flowing back to the battery when the engine starts is almost certainly going to be way above design parameters and a prime opportunity for a battery explosion. I wouldn't want to melt an Elan that way.

Yes, you could implement a protection circuit to prevent reverse flow.


if the alternator is operating normally (i.e. regulator not damaged) I'm not sure where a flow back current wold be coming from : Lithium Ion batteries having a higher rest voltage than Lead ones, current is still going to flow in the same direction if not disconnected immediately after start, though at a lower rate (and even if the alternator tried to put out 16+ V, the lead battery will still be there to quiet him down...). My guess is phones and other Lithium Ion battery issues are coming from internal shorts rather (which can come from mechanical or thermal damages).
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PostPost by: pharriso » Fri Jul 14, 2017 2:34 pm

ericbushby wrote:Phil and Steve,
A 400 amphour battery will give 400 amps for 1 hour, or 1 amp for 400 hours.
The maximum current available depends on its internal construction.
This is a 6 amphour battery so it will give 400amps for 6/400 - 0.015 hours or 54 seconds as suggested by nmaudit above.
If we allow for 50 percent losses due to small cables, internal resistance in the battery etcetera we now get 27 seconds.
My car takes 160 amps to start it so it will last for 67.5 seconds, whlch, if there is no problem except a flat battery should be enough to start it.
I hope this explains it and please notice that I have not said this is a good idea.
I think some small jump leads to re-charge you car battery for a few minutes from your new friends car is more likely to work and you are not carrying a high energy lithium battery.
Eric in Burnley
1967 S3SE DHC


Eric, thanks for explaining the theory, my skepticism is based on the small size of the power supply.

I'd have to see it to believe it. :-)

Doubting Thomas.
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