Charging 2 12v batteries separately

[LightShow]

hey all,

I've recently followed through on that new repeater design for the radio network at cadets (old forum post) however the plans have changed slightly from the original post since I have now realised that the repeater has two dc inputs one for backup (I assume for a 12v battery backup) and a dc in which must have been used for a plug pack long ago.. however since this whole repeater setup has been moved from section to section I have lost all the manuals and the original dc plug.

I have successfully set up the repeater with one 120Ah battery (for daytime use) and one 80ah battery (for nighttime use) this also has a solar charge controller by redarc hooked up which allows me to check battery levels and charge via solar if need be.

my questions are

- is there a way or a device that I could use to charge both batteries from 240v at the same time without putting them into parallel or series.

- what would be the best way of isolating both batteries from the load without isolating any 240v charging circuitry

- what over discharge device would be the best for something like this? and would I need 2 or could it somehow be used with one?

- is there anything from a professional perspective that I am missing? I am totally open to constructive criticism


additional info

- all cables used in the setup are rated for 30A loads
- the load will be pulling 18A max (while Transmitting and receiving)
- the reason for the lower Ah battery during the night is because there is barely any radio comms and such a bigger battery isn't needed
-the repeater/load is a Kenwood TKR-751 repeater
- the whole assembly has been modified to fit into an army CP box for waterproofing as well as ruggedness.
- both inputs are being used on the repeater by a battery meaning that the "DC IN" is the 120Ah and the "backup" is the 80Ah


Regards, Lightshow

 

[LightShow]

bump?

 

[(*steve*)]

You could use 2 chargers if the batteries are completely isolated (and must remain so)

 

[LightShow]

You could use 2 chargers if the batteries are completely isolated (and must remain so)

the only way the batteries are connected is through the solar charge controller which doesnt connect the batteries to each other anyway.

I was wondering if there was a charger which supported this? charging two batteries at the same time when they are completely isolated?

 

[kellys_eye]

- is there a way or a device that I could use to charge both batteries from 240v at the same time without putting them into parallel or serie

Series blocking diodes - suitably rated for current of course - from the charger to each battery will 'isolate' them but you may have to adjust your charger output voltage to compensate for the 0.7V drop they introduce.

 

[LightShow]

Series blocking diodes - suitably rated for current of course - from the charger to each battery will 'isolate' them but you may have to adjust your charger output voltage to compensate for the 0.7V drop they introduce.

could you give me some more information on this method?

 

[Wireaddict]

If you choose the blocking/steering diode route you can use Schottky diodes which have lower forward voltage drop. A 1N5817, for example, has a forward drop of about 0.2V. 1 amp Imax & 40 PIV.

 

[LightShow]

If you choose the blocking/steering diode route you can use Schottky diodes which have lower forward voltage drop. A 1N5817, for example, has a forward drop of about 0.2V. 1 amp Imax & 40 PIV.

this sounds great! does this mean that it is theoretically "splitting" the charging current between both batteries?

 

[Wireaddict]

I'm not even sure it could be done without seeing all your requirements &/or a schematic but the concept of the blocking &/or steering diodes allows the batteries to supply power to their loads while the diodes route charging current to them independently of the loads. If that can be accomplished then Schottky diodes would deliver a little more charging voltage because they have less forward voltage drop. (That's why they're sometimes used in "crystal" radios & AM detectors but that's another topic.)

 

[Dave 2000]

Unsure if I am of much help here but here goes.

I do a lot of off road and expedition trips in my vehicle. There are two batteries in parallel during the charging process, if charging is stopped or one battery is being drawn from the batteries seperate.

This is accomplished via a dual sense voltage sensitive relay capable of carrying 500 amps, whilst I know what I am talking about when it comes to typical vehicle electrics (not electronics) I may be way off base, if so then I apologise for this useless post. 8>(

Regards

Dave

 

[Wireaddict]

This begs a few questions: Do you have any info on these voltage sensitive relays? Do you need one relay per battery? Can both negative battery leads be connected together or must they be totally isolated from each other also? (I suspect the common/neg. battery leads are connected to the repeater chassis by the jacks.) What would happen if both batteries (+ & - leads) were permanently connected to the repeater without taking the weaker battery offline? (I suspect there may be isolating diodes connected to + side of the 2 battery jacks inside the repeater so that the stronger battery always operates it.) If the voltage sensitive relays have at least one low current/pilot-duty aux. contact &, better yet, if there's one relay per battery we could probably design something that would connect each battery to the charger as it discharged but this may be overkill. It's possible all you need is to connect steering diodes between the positive charger lead & the positive lead from each each battery & all the neg. cables together.

 

[gunnadoo]

hi LS.,i am a little bit confused here, you have mains power to charge these batteries. why have 2 batteries when u could use a psu for the main dc input and the battery as the ups

the batteries are connected is through the solar charge controller which doesnt connect the batteries to each other anyway.

if you are charging 2 batteries with 1 solar cc the batteries must be connected somehow. either parallel , series or the + 0r - terminals connected to each other. i am off grid and use plasmatronic charge controllers pl 20/40/60/80 AMPs . you can program them to charge 2 batteries ,but the + terminals must be connected , they can protect battery via LVD and nearly anything else you want it to do.also 18A is a lot of current. how much time would you be drawing this amount of current from battery at nite ,without any charge