I need diodes for dual a123/life battery rx setup

[Merlin spit]

after much reading ive decided to use two a123s with a switch each for redundancy .now i know the opinon  is you can use these a123s with out regulators.but im looking at using the diode to drop voltage a little and protect against the unlikely of a short in one battery.

 

now i need to know where and what ones to get? i presume something that's 8A capable would be fine.

[GONZO]

One of THESE from Maplins ?????

[Former Member]

[This posting has been removed]

[Paul Adams]

If you put diodes in the feed from each battery, you will not need a switch as the diodes will only supply the voltage from the highest voltage battery to the receiver / circuit / motor. Remember however that you will need to add a separate charging lead to each battery which does not pass through the diode, as the diode will be reverse biased to the charging current.  

[Merlin spit]

thanks guys ,just for clarification  the diodes should be soldered into the posstive or negative wires?

 

i presume putting the diode the receiver side of the switch  will alow me to charge via the charge socket on the switch

[GONZO]

Part 1/ Diodes in +Ve leads. As you are useing a two switch arrangment feed the Rx at each end of the servo connector block to distribute the load (with Y leads if required).

Part2 / Yes.

[Vecchio Austriaco]

every diode will reduce the voltage for 0.7 volts. (silicium - which are most common these dauys) so if you need 2 volts reduction put 3iodes in series (2.1 volts drop)

cheers VA - only 2 hours 5 mins to 2011 here!

[Former Member]

[This posting has been removed]

[Bob Moore]

I wouldn't worry about reverse current unless you are going to leave it for a very very long period.  Months and months.The reverse current of the Maplin diode linked is 5 uA.  5 micro amps.  ie 5 millionths of an amp.  Or 1/200 of a milliamp. I would think the natural discharge rate of the batteries would be far more than than that?

[Ultymate]

Everyone I know whose using A123s does so without any sort of voltage regulation, this seems  to be one of the main attractions along with the fact that they can be charged at extremely high charge rates 

[crispin church]

i have used A123 2cell without any cut down for over 2 years without any problems on 35meg and 2.4 gig

just one thing make sure you balance charge them often

[Phil 9]

what about a regulating switch

hobby king           power box

Edited By Phil B on 08/11/2011 19:49:49

[fly boy3]

Excuse my lack of knowledge but what does " dual power redundancy" actually mean. Cheers

[Phil 9]

FB3 it just means two receiver batteries (dual power) that are a back up for each other. ie if one fails the other will still supply power. (one pack is redundant at any one time)

[fly boy3]

Thanks Phil, I think this type of set up is normal for the LMA boys ?. Cheers

Edited By fly boy3 on 08/11/2011 20:48:04

[Steve Hargreaves - Moderator]

Posted by Phil B on 08/11/2011 19:49:10:

what about a regulating switch

hobby king power box

Edited By Phil B on 08/11/2011 19:49:49

Those units look exactly the same to me.....can it really be that there are two factories turning out identical looking units?

 

Or are those Powerbox stickers just mightily expensive........

[Martin Harris - Moderator]

It wouldn't be the first example of badge engineering - or of cloning. Literally a case of pay your money and take your choice unless an insider spills the beans...

[Bob Cotsford]

the Powerbox one has the facility to change the cutover voltage to suit LiFe, the HK one doesn't. The PB one also claims to use separate regulators and comparators for each battery where 'others use a single regulator'.

[Steve Hargreaves - Moderator]

You could well be right Bob.....obviously I don't know what goes into either of them.....the HK description hints at two regulators.....yet even if the HK version only has one regulator against the two in the Powerbox unit so we double the price of the HK unit to 28USD to pay for another regulator that's still a heck of a difference!!!

 

But I do think its intriguing that the two units look exactly the same.....same type of LEDs & pushbuttons etc.....Of course HK could have simply copied the design of the PowerBox one......

[Bob Cotsford]

or had it made in the same factory!

[Stephen O'Neill]

I have just purchased some 6A diodes to reduce the voltage from my 123 Rx batteries. I was expecting to get a 0.7V reduction across the diode but only getting a 0.2V. Please excuse my lack of knowledge on this subject but I would welcome some guidance on where I am going wrong? The markings on my silicon diodes are: 6A100 A38

[michael cawood]

are you measuring the open circuit voltage. i think you need to be pulling power i.e. connected to something to get the full drop of 0.7v.

[Stephen O'Neill]

Hi Miichael, you were absolutely right. I completely forgot about measuring the voltage with everything connected up, thanks

[Peter Beeney]

Stephen, - I’m afraid I don’t recognise that number, do you know exactly the specification of your diodes? Also have you any means of checking your voltmeter? Any unexpected results, and it’s always a good idea to check the measuring instruments first, on the very odd occasion that can save a lot of flying time!

After doing a very quick check, I came up with the following results on a couple of diodes, the forward volt drop measured directly across the diode with varying loads.

A standard 6A silicon, P600A. Open circuit, 0.0093V. 5mA load, 0.6671V. 1A, 0. 8159V.

A Schottky 16A MBRF 1645. Open circuit, 0.0001V 5mA load, 0.2578V 1A, 0.3815V.

Any other similar pair will always give slightly different readings. This is one of the reasons they don’t like sharing the load when connected in parallel; and the forward drop is variable with the current flow. I do know that a 1A diode, when carrying a current of 1A, can drop up to at least 1 volt across the connections.

In very general terms, as you imply, the forward drop for a silicon is 0.6 - 0.7 volt, whilst that of a Schottky is around the 0.2 volt mark. So is it perhaps possible you have Schottky diodes?

Everything else being equal, I think it’s unlikely that you will get any standard silicon diodes with a forward volt drop as low as 0.2 volts…

PB

[Stephen O'Neill]

Hi Peter and thanks for your input.As always, you have come out with some very good information. The only spec info I have is 6A 1000V however the shop I bought them from is a local electronics supplier with a good reputation. I subsequently took the measurements with the receiver and servos connected up and it had the desired effect with a reading of 6.58V and 5.86V before and after the diode respectively. I have not had my tester calibrated but I expect it is near enough the mark as it is a new Graupner clamp meter. I will double check with a new field tester I have and let you know.

Again, many thanks gents!

Steve