The Ideal Diode / Leisure battery switch, charging thingy

[Aethelric]

You could then by 40 Lidl AA battery chargers and run a VERY long mains lead (length dependant on the distance to your destination) with 8 extension leads plugged into each other and keep them charged up - doesn't sound too difficult...............

Well, I guess that would work but hopefully JnK may come up with something a little more elegant.
I think we'll start to see Lithium batteries as leisure batteries within a year or two.

Dave

[mikeonb4c]

I think we'll start to see Lithium batteries as leisure batteries within a year or two.

Dave

Very exciting if they become affordable as pound for pound (weight) you could get a whole whack of AmpHrs over lead/acid for the same weight. I'm not an electrochemist but can they easily be persuaded to give out 12v or is some electrickery needed?

Mind you I fear they may remain v expensive making them a highly desirable 'nick' just sitting under your bonnet

[Aethelric]

I think we'll start to see Lithium batteries as leisure batteries within a year or two.

Dave

Very exciting if they become affordable as pound for pound (weight) you could get a whole whack of AmpHrs over lead/acid for the same weight. I'm not an electrochemist but can they easily be persuaded to give out 12v or is some electrickery needed?

Mind you I fear they may remain v expensive making them a highly desirable 'nick' just sitting under your bonnet

Lead acid batteries only give out 2V per cell Mike, but a battery has 6 cells in series. A Lithium battery may be smaller and lighter AH for AH, but you would need less Ampere hours, as you can safely use ALL of the power from a Lithium battery. Fully discharging a lead acid battery is very detrimental. I think it will be while before they could supply the starting current, but for the steady drain for a leisure battery they should be ideal.

[John and Kim]

Ok you can stop the discharge through the FET by using back to back N types, twice as much power loss but hey it works!

Yes Lithiums are great and I'm fortunate to own some AA (?A/Hr) and D (5A/Hr) types and use them in portable radios.
They're light and to charge you just make sure exactly 4V2 is across each cell; remember the warning; "May vent with flame!" (if incorrectly charged). Seem to be hard to find in singles and got mine from a (modern) military radio backpack.

The thyristor is a good idea............hmmmmmm..

JnK.

[John and Kim]

I forgot to ask...........

What's the amount of charge current I can expect to flow into the leisure battery when it's fully discharged?

JnK.

[g8dhe]

What's the amount of charge current I can expect to flow into the leisure battery when it's fully discharged?

I would have thought more than enough to damage the cells! If it has been fully discharged then it needs management of the current to prevent buckling of the plates, I would have thought a trickle charge to begin with, say 3-5 Amps and then slowly rising as the charge builds up and finally tailoring off on its own accord as the cell voltage returns to normal. I don't think I would want to exceed about 15 Amps at any point for a leisure battery (for a starter battery which is designed for much higher peak its a different matter).

[g8dhe]

Ah just done some googling and found this sitehttp://www.batteryuniversity.com/index.htm if you click into Part 1 and look at BU13 it has some good suggestions.

[John and Kim]

Thanks Geoff, but I still need to know how much current the leisure battery will draw when discharged, not how much to give it.

I've heard rumours of blowing fuses and need to know what limit to set on my 'Device'!

i.e 50A, 85A, 100A. Is it a case it will take a great deal of current for a brief time then settlee to something more manigable?

JnK

p.s. G8DHE, is that your callsign OM?

de M0VFR.

[g8dhe]

But that's thing that needs protecting against. I would measure the current being drawn and the voltage across the L/B, then use those factors to limit at the chosen value for the battery concerned (remember the battery could vary from about 70AH to 115AH depending what's fitted) or perhaps even use PWM to create an average current in which case I would still limit at 15A myself.

Yup the callsign is unique so I tend to use it most of the time for my ID, plus it identifies me to other amateurs

[mikeonb4c]

Lead acid batteries only give out 2V per cell Mike, but a battery has 6 cells in series. A Lithium battery may be smaller and lighter AH for AH, but you would need less Ampere hours, as you can safely use ALL of the power from a Lithium battery. Fully discharging a lead acid battery is very detrimental. I think it will be while before they could supply the starting current, but for the steady drain for a leisure battery they should be ideal.

Grrr ths forum is annoying. Why don't I spot when someone has replied to a post I made - Aethelric must think i'm being uncommunicative (apologies dude!).

Yup, got the lead/acid 2v per cell thing. I suppose what I'm asking is if NiMh give out 1.5v per cell (do they always?) then I suppose 8 in series is needed and Richards your fathers brother. Job done. Just need to get cost down and watch out for the tea leaves.

[Aethelric]

Lead acid batteries only give out 2V per cell Mike, but a battery has 6 cells in series. A Lithium battery may be smaller and lighter AH for AH, but you would need less Ampere hours, as you can safely use ALL of the power from a Lithium battery. Fully discharging a lead acid battery is very detrimental. I think it will be while before they could supply the starting current, but for the steady drain for a leisure battery they should be ideal.

Grrr ths forum is annoying. Why don't I spot when someone has replied to a post I made - Aethelric must think i'm being uncommunicative (apologies dude!).

Yup, got the lead/acid 2v per cell thing. I suppose what I'm asking is if NiMh give out 1.5v per cell (do they always?) then I suppose 8 in series is needed and Richards your fathers brother. Job done. Just need to get cost down and watch out for the tea leaves.

he he!
I was browsing the web looking for info on Lithium batteries, and I found out that its detrimental to keep them fully charged! Sods Law overrides everything.

Dave

[Manny]

but I still need to know how much current the leisure battery will draw when discharged

JnK it is probably difficult to quantify as it all depends on how discharged the battery is, on the resistance of the wire etc. But it is big, my 25 amp fuse just went with a flash when the relay switched on. If it is that discharged it is probably going to be damaged. What I found out though was that connecting a 24W light bulb between the SB and the LB with engine running lit up the bulb quite brightly for a few minutes and then as the LB voltage rose the bulb began to dim. At that point I replaced the fuse and all was well, except the battery did not last very long after letting it go flat a few more times. (forgot to swith off cool box). I was going to build a circuit to detect the LB voltage and if it was too low to limit the charging current till the voltage rose, but that would not protect the battery from still being over discharged. So instead I incorporated a circuit to disconnect the LB from the load when it reaches just below 12v. No more blown fuses and hopefuly a longer lasting LB

Manny

[John and Kim]

OK, (don't get too excited!) Nearly there..................


To recap this 'Device' will be inserted in the +Ve lead of the main battery and connect to the +Ve terminal of the leisure battery, it will need a good ground and will be SMALL! because it will use 'Semiconductors!'

It will allow the leisure battery to be charged from the main whilst maintaining complete isolation, any current greater than 12A(???more/less???) will cause the 'Device' to PWM the o/p and also drop the Volts a little due to the action of the circuit, I'm hoping this will help to limit the inrush of 'I' to a deeply discharged battery.

I've set it up to only switch on and conduct 'I' at 13V5(???) any less and it'll be 'Off'. So will only charge 'Leisure' when 'Main' is full.

Reverse 'I' is impossible but can make it so at the flick of a switch (if you really needed to charge the Main batt from the Leisure batt?)
I can also use the same circuit slightly modified to monitor the o/p of the leisure battery and isolate the load when 'V' drops below 11V5 (suggestions please) and will also turn off when a preset current (???) is reached.

So if I can get the thing to work you may want to buy 2!

This is 'Work In Progress' and can't guarantee anything here but it may work well for lead acid charging / isolation / monitoring.

I'll post as soon as I've got a finished model and will be wanting some willing 'Victim' to test it!

Charging batteries isn't too difficult it's looking after them that's the problem and I'm hoping my 'Device' may go some way to sort out this 'Problem'

JnK.

[mikeonb4c]

OK, (don't get too excited!) Nearly there..................


To recap this 'Device' will be inserted in the +Ve lead of the main battery and connect to the +Ve terminal of the leisure battery, it will need a good ground and will be SMALL! because it will use 'Semiconductors!'

It will allow the leisure battery to be charged from the main whilst maintaining complete isolation, any current greater than 12A(???more/less???) will cause the 'Device' to PWM the o/p and also drop the Volts a little due to the action of the circuit, I'm hoping this will help to limit the inrush of 'I' to a deeply discharged battery.

I've set it up to only switch on and conduct 'I' at 13V5(???) any less and it'll be 'Off'. So will only charge 'Leisure' when 'Main' is full.

Reverse 'I' is impossible but can make it so at the flick of a switch (if you really needed to charge the Main batt from the Leisure batt?)
I can also use the same circuit slightly modified to monitor the o/p of the leisure battery and isolate the load when 'V' drops below 11V5 (suggestions please) and will also turn off when a preset current (???) is reached.

So if I can get the thing to work you may want to buy 2!

This is 'Work In Progress' and can't guarantee anything here but it may work well for lead acid charging / isolation / monitoring.

I'll post as soon as I've got a finished model and will be wanting some willing 'Victim' to test it!

Charging batteries isn't too difficult it's looking after them that's the problem and I'm hoping my 'Device' may go some way to sort out this 'Problem'

JnK.

Sounds really interesting JnK and well done. I have an inadequate VSR on mine that I currently have to protect with 30amp fuses. I keep meaning to upgrade it but as I'm watching the £ and as my setup is coping OK, I just live with it and avoid deep discharge ( ). If your idea passes muster on test, are you thinking of offering them for sale and at what cost if so?

Once again, well done. Great to see so many innovators on this site. Better than listening to hedge fund managers by a clear mile

[John and Kim]

Yes I've seen my shares go from $5.20 to 80c in less than two weeks, well that's telecomms and they were at $70 at the height of 3G!

Anyway back to the 'Project'. I have it simulated and running well and already have a 'Real' one working with UnderVolts but have not implemented the PWM 'Feature' yet. I'm trying to keep it simple and hence costs down and can't make the PWM action variable and don't really think that's necessary as I just need to turn the 'Device' on and off when a large current event happens and this will then drop the voltage (slight problem here as it will generate heat, not a lot but enough to be concerned about) and this will hopefully lessen the amount of current the leisure battery will be drawing; so will drop a Volt at 60A.

I need to do some 'Real' experiments and am not far off and yes they will be for sale. I'll be giving a few away (providing it passes a few tests) and they won't be silly money anyway but can't say till it's finished!

Yes one of those seemingly simple but rather difficult to do things to do.

JnK.