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 Posted: Wed Dec 4th, 2019 03:42 am
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Tom Harbin
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Rick,

I'm not sure I really believe what I just wrote. In thinking about how LiPos age, I think the parallel-connected batteries will have issues as well. As LiPos age their internal resistance increases. That means that if I apply a re-charge voltage to two parallel-connected batteries with different internal resistances one will charge more quickly than the other. The only safe way to deal with that is to stop charging when the fresher battery reaches capacity. The pair will lose capacity just like the series-pair but it won't need a three (or more) wire balance charger to individually charge the batteries, so a simpler circuit. In fact it may even be that a series-connected pack might age more slowly if charged by a high-quality balance charger (many lower cost balance chargers are really just charging the pack in parallel through the balance connector). I may be all wrong on this but I'm thinking that 1S1P is really the only drama-free LiPo solution.

Tom 

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 Posted: Wed Dec 4th, 2019 07:48 am
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davecttr
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There are voltage regulators that can give over 80% efficiency for an output of 12V and a input of 3.3V. The Pololu U3V70Fx series is one. The problem is the size, at 48x15x10.5mm they are bigger than the receiver!. The smaller regulator I use is 13x8x3mm but with a single lipo is only good for up to 275mA 12V locomotives, or over 800mA if 2 lipos are used.

I think this is the problem Protocab have with their integrated voltage regulator. It is designed for up to 500mA but only at lower voltages.



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 Posted: Wed Dec 4th, 2019 10:06 pm
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Rick Dow
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I have always found the various charging scenarios confusing.

I will probably stick with unwired rails and my usual removal by hand of my Li-Pos from their tenders, then charging them externally in a balanced manner with my charger. 

After watching one swell up and catch fire (do to my clumsy crossing of the wires) I just feel better and I really don't find it to be much of a bother.  

I may be just another spoil sport so apologies in advance to all who find me too conservative.




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 Posted: Wed Dec 4th, 2019 10:50 pm
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Bob Walker
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The science of rechargeable batteries is complex. I am a retired EE with extensive work experience with battery powered electronic devices. LiPO batteries are new and somewhat unique compared with earlier types like NiCd and NiMH. For now, best bet is to remove the battery and charge it on a balanced charger. An important step is to monitor battery voltage. All of my battery powered locos have a jack which permits easy check of battery voltage.On-track charging needs to be carefully approached and is not by any means a simple project.
Bob

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 Posted: Fri Dec 6th, 2019 08:04 am
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fallen
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Just a thought on the parallel charging question, the two or more cells in parallel will have the same voltage applied. If one draws more current due to a lower internal resistance and as a result charges more quickly, its internal voltage will rise and this will reduce the current.

So it might be that if you charge to a final voltage as most LiPo chargers do,then they both end up at the same state of charge.

As has been said, its not straightforward.

Frank

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 Posted: Fri Dec 6th, 2019 03:45 pm
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davecttr
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fallen wrote: Just a thought on the parallel charging question, the two or more cells in parallel will have the same voltage applied. If one draws more current due to a lower internal resistance and as a result charges more quickly, its internal voltage will rise and this will reduce the current.

So it might be that if you charge to a final voltage as most LiPo chargers do,then they both end up at the same state of charge.

As has been said, its not straightforward.


As I understand it charging batteries connected in parallel is the same as charging a single battery as they behave as a single battery and will balance themselves to equal voltage without any outside influence.

Charging batteries connected in series is a lot more complex involving circuitry etc to handle switching and voltage monitoring
Yes, you could just charge the first battery to 4.2V and then charge the second one to 4.2V, they would be balanced, but if you stopped the charge part way through they would not be balanced. Balance chargers switch back and forth between the batteries to equalise the voltage ??



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 Posted: Sat Dec 7th, 2019 11:07 am
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Tom Ward
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Last week I wrote to Neil Stanton about charging batteries through the rails for S-Cab.  Copied below are his two replies.  The original reply is further down.  I replied to his second one to clarify that I should have said "power supply" rather than "charger" in my FR post.  I'm posting his replies here  just to help clarify info on the S-Cab system discussed in this thread.  Thought it might be helpful to have it straight from the source.  I'll be using the BPS-4 in each locomotive and his 12.5vdc power supply to charge the tracks in the roundhouse through a selector switch.
- Tom


Hi Tom,
I just reviewed your inquiry after reading some FreeRail posts.I assumed you were using BPS-v4, which recharges from track power.However, you stated"I plan to have the charger run through a selector switch. Does this mean the charger is external to the loco?  If so, your plan has serious problems:
  1. There is polarity problem that requires the loco always be oriented in same direction when in the roundhouse
  2.  More serious, the battery in the loco must connect to wheel wipers in order to connect thru rails to the charger. As a consequence, the battery can easily be short-circuited in a derailment.  A diode is required to eliminate this risk, but this messes up charging due to the diode voltage drop (approx, half a volt).
External charging is only necessary for multi-cell series battery packs (typically 3S or 4S) using a multi-pin polarized connector; not the rails.
If you use a 3S battery pack (nominally 11.1 volts), you do not need S-CAB BPS and will need an external charger with cell balancing.If you use S-CAB BPS with a 1P or 2P battery, your plan is easy, as I explained in previous email.
Neil.


Hello Tom,
By default, BPS charges battery using track voltage. Your locos must have track pick-up (wheel wipers) and best power source for rails is a well-filtered DC power supply. Charging voltage can be any value between 7 and 15 volts, but 12.5 volts is perfect. Do not use a hobby-type power pack for battery charging. A commercial DC supply is an option.
Neil.




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"When I die I want to go quietly in my sleep like my grandfather. Not screaming in terror like his passengers."
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 Posted: Sat Dec 7th, 2019 05:20 pm
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Bob Walker
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One of the keys to on-track charging is to have the pickups active only when the loco is on the charging spur line. I have experimented with this and believe I have developed a workable setup.The other important element is careful monitoring of battery voltage and charging current during the recharge cycle.
Bob

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 Posted: Sun Dec 8th, 2019 11:28 pm
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Tom Harbin
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Tom Ward wrote: Last week I wrote to Neil Stanton about charging batteries through the rails for S-Cab.  Copied below are his two replies.  The original reply is further down.  I replied to his second one to clarify that I should have said "power supply" rather than "charger" in my FR post.  I'm posting his replies here  just to help clarify info on the S-Cab system discussed in this thread.  Thought it might be helpful to have it straight from the source.  I'll be using the BPS-4 in each locomotive and his 12.5vdc power supply to charge the tracks in the roundhouse through a selector switch.
- Tom


Hi Tom,
I just reviewed your inquiry after reading some FreeRail posts.I assumed you were using BPS-v4, which recharges from track power.However, you stated"I plan to have the charger run through a selector switch. Does this mean the charger is external to the loco?  If so, your plan has serious problems:
  1. There is polarity problem that requires the loco always be oriented in same direction when in the roundhouse
  2.  More serious, the battery in the loco must connect to wheel wipers in order to connect thru rails to the charger. As a consequence, the battery can easily be short-circuited in a derailment.  A diode is required to eliminate this risk, but this messes up charging due to the diode voltage drop (approx, half a volt).
External charging is only necessary for multi-cell series battery packs (typically 3S or 4S) using a multi-pin polarized connector; not the rails.
If you use a 3S battery pack (nominally 11.1 volts), you do not need S-CAB BPS and will need an external charger with cell balancing.If you use S-CAB BPS with a 1P or 2P battery, your plan is easy, as I explained in previous email.
Neil.


Hello Tom,
By default, BPS charges battery using track voltage. Your locos must have track pick-up (wheel wipers) and best power source for rails is a well-filtered DC power supply. Charging voltage can be any value between 7 and 15 volts, but 12.5 volts is perfect. Do not use a hobby-type power pack for battery charging. A commercial DC supply is an option.
Neil.




Tom,

If I read this correctly, if you use a BPS-v4 you can charge from a CLEAN DC source. The BPS-v4 has the charger built in so polarity issues are taken care of on-board. I did think I remembered that you could also charge from DCC but maybe that was just the cut-over to track power not charging. This also means there is no need for a selector switch.

HOWEVER, Neal's reply brought up something I had not considered. If you have track wipers you still need to gap like for powered rail or you will short the battery, OR, you can have the track wipers only active when in a charging area (I envision maybe under-engine reed switches with under track magnets in charging station areas to activate the wipers). Just a thought and maybe all wrong but it does say that the common idea of not bothering to gap the rails when building for RCBP could be an issue with on-track charging. I was just going to leave the wipers and connect in a BPS-v4 but I was not going to gap the rails. The BPS-v4 may have some kind of short protection for the battery (besides the fuse) but I don't remember reading about it.

Looks like I need to do more thinking.

Thanks,

Tom

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 Posted: Mon Dec 9th, 2019 01:44 am
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Rick Dow
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So am I then to assume from the preceding posts and also from the S-Cab web site that multi cell Lipo batteries may be safely charged and "balanced" when utilizing on-track charging with a BPS v4?    I notice in the photo a one cell Lipo.


The web site states as follows:   Battery charging, protection and switching are also included in one, small double-sided circuit board assembly.

Rick



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