Summary - this post (a) outlines the results of tests made to check the shelf-life and self-discharge rates of readily-available 12 volt Li-ion packs and (b) makes recommendations about the type of 12 volt Li-ion pack to buy and how to install it in terms of connections. Initial results are presented in a graph at the end of this first post. They will be updated as testing continues.
In various threads since February, I've summarised the invariably positive experiences of using cheap 12 volt 6800 milliamp/hour Li-ion battery packs purchased from Chinese suppliers via eBay. However, in one of the more recent threads, GSCer MRail asked something which I'd been wondering myself. Just how good are these packs in terms of charge retention? This is linked to the different design of the two types of pack most commonly available. I won't try to cover all the ground of the previous threads, nor repeat safety warnings. Suffice it to say that if you treat the two cell types reviewed with normal respect and don't do anything you wouldn't do with other batteries (e.g. shorting them/ disassembly) they are perfectly safe.
For other threads and Li-ion technology, see the following:
http://www.gscalecentral.net/m160892
http://www.gscalecentral.net/m148031
http://iccnexergy.com/articles/1244/lithium-ion-battery-assembly-challenges/
For newbies, there are two generic Li-ion packs available on eBay which, for obvious reasons, I call the black and blue types. Internally the packs are identical. They each contain three 3.7volt Li-ion batteries with both individual protection circuits and a thermal cutout protecting the pack as a whole. Externally, they are utterly different.
The black pack is housed in a hard plastic shell and measures 107mm by 64mm by 25mm, though the necessary connecting plug will require more length. The blue pack is wrapped in plastic film producing a rigid block, but obviously inherently less resistant to knocks or "stab wounds" than the black pack. The blue pack has the advantage of thinness, measuring 103mm x 53mm x 20mm though the wires which exit the pack effectively add a few millimetres in both length and width.
The critical element for review here is the way the batteries can be connected externally. This is the determining factor in battery discharge. I'll deal with each in turn, black first.
The black pack has a single socket connection, used for both charging the battery and supply to whatever load the battery powers. It is controlled by the prominent on/off switch which is illuminated when the socket is "live". The battery can only be used with the switch on. As will be seen, this has implications for use in an inaccessible location such as a loco body.
As supplied, black packs come with a connecting lead with 2.1mm plugs on each end. In most circumstances, G scalers will want to cut this to attach to a control circuit. Hence the half lead terminating in a connector block as shown on the right of the picture above. For charging purposes, users have the choice of either manually swapping between the supply lead and the charger's lead, or linking a single lead to a charging socket via a switch which allows either charging or discharge, but not both at the same time. Obviously the manual method is only possible when there is easy access to the battery, such as in a trail car.
The blue pack has two leads, one intended for charging (2.1mm socket) and the other for supplying power (2.1mm plug). As supplied these are firmly taped to the battery ensuring that they cannot be connected together.
Although the blue pack has a switch, together with a tiny "tell tale" light alongside (see second picture), the switch only controls the supply lead. The charging lead is permanently live at all times and hence is a short-circuit hazard. Cutting through the charging lead is definitely NOT recommended. Beware!
Discharge graph:
So what about the shelf-life and discharge questions and do those illuminated switches take noticeable amounts of power? The graph below shows the results of a few weeks testing. In all cases, the packs were simply sat in my cellar, not powering anything except, where shown, the light activated by the pack's switch.
The yellow line shows that the black pack rapidly loses voltage with the switch on. So fast that after 17 days there is no usable charge left. This rather surprised me! I wonder if the switch uses a small "conventional" bulb rather than an LED? This self-discharge will be an issue if the pack (loco) is used rarely. On the other hand, the self-discharge effect may be irrelevant if a battery is used at least once per week, though technically more discharge/charge cycling will be required and the battery's useful life shortened slightly.
The purple line is the same test, but for a blue pack with the switch on. Loss of charge is obviously much slower. In my view, for most users leaving the switch on will be a non-issue. Measurements will be continued until the pack drops below 11 volts and a revised graph posted.
Finally, the blue line represents a pack whose switch is off. There is no self-discharge measurable at all within the limits of my meter. Theoretically, Li-ion cells are expected to lose 3% of charge per month. That compares, by the way, to 30% for ordinary nickel metal-hydride (NiMH) cells, with "low self-discharge" (LSD) NiMH cells somewhere in between. Again, measurements will continue and be reported.
Conclusions
1) The blue pack design is preferable to the black pack unless the rigid shell of the black pack is absolutely necessary.
2) The black pack is suitable for use in trail cars, when the battery switch can be turned off after a running session.
3) The blue pack is the preferred type for installation in an inaccessible location or when running sessions are infrequent.
4) For maximum capacity, the blue pack should be connected in a manner which allows power to flow with the switch (and light) off. This depends on connection design, as outlined below.
Blue pack users have various choices in making connections:
1) tape up the exposed supply lead and use the charging lead for both charging and supply, manually switching cables. Probably only an option in a trail car.
2) use the charging lead for charging and connect the supply lead either directly to its load or (preferably) via an on/off switch. This requires the battery switch to be on at all times and risks both charging and discharge happening at the same time. Those with more knowledge can advise if this is really a bad thing.
3) tape up the charging lead, cut into the supply lead (with the battery switch off!) and link the supply lead to both a charging socket and speed controller via a switch which allows either charging or discharge, but not both at the same time. This approach requires the blue pack's switch to be on at all times.
4) cut into the supply lead and use the severed plug end as a mate for the charging lead with the other end connected as described in (3). Tape up any exposed wires from the supply lead.
Option 4 is my recommended approach. It means the battery switch can be left off and also makes exchanging the battery at some future point a simple plug swap, rather than unscrewing or unsoldering connections.
In various threads since February, I've summarised the invariably positive experiences of using cheap 12 volt 6800 milliamp/hour Li-ion battery packs purchased from Chinese suppliers via eBay. However, in one of the more recent threads, GSCer MRail asked something which I'd been wondering myself. Just how good are these packs in terms of charge retention? This is linked to the different design of the two types of pack most commonly available. I won't try to cover all the ground of the previous threads, nor repeat safety warnings. Suffice it to say that if you treat the two cell types reviewed with normal respect and don't do anything you wouldn't do with other batteries (e.g. shorting them/ disassembly) they are perfectly safe.
For other threads and Li-ion technology, see the following:
http://www.gscalecentral.net/m160892
http://www.gscalecentral.net/m148031
http://iccnexergy.com/articles/1244/lithium-ion-battery-assembly-challenges/
For newbies, there are two generic Li-ion packs available on eBay which, for obvious reasons, I call the black and blue types. Internally the packs are identical. They each contain three 3.7volt Li-ion batteries with both individual protection circuits and a thermal cutout protecting the pack as a whole. Externally, they are utterly different.
The black pack is housed in a hard plastic shell and measures 107mm by 64mm by 25mm, though the necessary connecting plug will require more length. The blue pack is wrapped in plastic film producing a rigid block, but obviously inherently less resistant to knocks or "stab wounds" than the black pack. The blue pack has the advantage of thinness, measuring 103mm x 53mm x 20mm though the wires which exit the pack effectively add a few millimetres in both length and width.
The critical element for review here is the way the batteries can be connected externally. This is the determining factor in battery discharge. I'll deal with each in turn, black first.
The black pack has a single socket connection, used for both charging the battery and supply to whatever load the battery powers. It is controlled by the prominent on/off switch which is illuminated when the socket is "live". The battery can only be used with the switch on. As will be seen, this has implications for use in an inaccessible location such as a loco body.
As supplied, black packs come with a connecting lead with 2.1mm plugs on each end. In most circumstances, G scalers will want to cut this to attach to a control circuit. Hence the half lead terminating in a connector block as shown on the right of the picture above. For charging purposes, users have the choice of either manually swapping between the supply lead and the charger's lead, or linking a single lead to a charging socket via a switch which allows either charging or discharge, but not both at the same time. Obviously the manual method is only possible when there is easy access to the battery, such as in a trail car.
The blue pack has two leads, one intended for charging (2.1mm socket) and the other for supplying power (2.1mm plug). As supplied these are firmly taped to the battery ensuring that they cannot be connected together.
Although the blue pack has a switch, together with a tiny "tell tale" light alongside (see second picture), the switch only controls the supply lead. The charging lead is permanently live at all times and hence is a short-circuit hazard. Cutting through the charging lead is definitely NOT recommended. Beware!
Discharge graph:
So what about the shelf-life and discharge questions and do those illuminated switches take noticeable amounts of power? The graph below shows the results of a few weeks testing. In all cases, the packs were simply sat in my cellar, not powering anything except, where shown, the light activated by the pack's switch.
The yellow line shows that the black pack rapidly loses voltage with the switch on. So fast that after 17 days there is no usable charge left. This rather surprised me! I wonder if the switch uses a small "conventional" bulb rather than an LED? This self-discharge will be an issue if the pack (loco) is used rarely. On the other hand, the self-discharge effect may be irrelevant if a battery is used at least once per week, though technically more discharge/charge cycling will be required and the battery's useful life shortened slightly.
The purple line is the same test, but for a blue pack with the switch on. Loss of charge is obviously much slower. In my view, for most users leaving the switch on will be a non-issue. Measurements will be continued until the pack drops below 11 volts and a revised graph posted.
Finally, the blue line represents a pack whose switch is off. There is no self-discharge measurable at all within the limits of my meter. Theoretically, Li-ion cells are expected to lose 3% of charge per month. That compares, by the way, to 30% for ordinary nickel metal-hydride (NiMH) cells, with "low self-discharge" (LSD) NiMH cells somewhere in between. Again, measurements will continue and be reported.
Conclusions
1) The blue pack design is preferable to the black pack unless the rigid shell of the black pack is absolutely necessary.
2) The black pack is suitable for use in trail cars, when the battery switch can be turned off after a running session.
3) The blue pack is the preferred type for installation in an inaccessible location or when running sessions are infrequent.
4) For maximum capacity, the blue pack should be connected in a manner which allows power to flow with the switch (and light) off. This depends on connection design, as outlined below.
Blue pack users have various choices in making connections:
1) tape up the exposed supply lead and use the charging lead for both charging and supply, manually switching cables. Probably only an option in a trail car.
2) use the charging lead for charging and connect the supply lead either directly to its load or (preferably) via an on/off switch. This requires the battery switch to be on at all times and risks both charging and discharge happening at the same time. Those with more knowledge can advise if this is really a bad thing.
3) tape up the charging lead, cut into the supply lead (with the battery switch off!) and link the supply lead to both a charging socket and speed controller via a switch which allows either charging or discharge, but not both at the same time. This approach requires the blue pack's switch to be on at all times.
4) cut into the supply lead and use the severed plug end as a mate for the charging lead with the other end connected as described in (3). Tape up any exposed wires from the supply lead.
Option 4 is my recommended approach. It means the battery switch can be left off and also makes exchanging the battery at some future point a simple plug swap, rather than unscrewing or unsoldering connections.
