Automation Direct 12vdc plc and a 4 channel 4-20ma input card all 12vdc

I am trying to setup an RTU with solar power and am trying to keep the power consumption low. This will have 3 pieces of equipment that I am trying to match voltages on.

1. The radio can be either 12vdc or 24vdc,
2. The data logger is 12vdc only,
3. And last is the plc which has to be an automation direct slave with a 4-channel 4-20ma input card.

I cannot seem to get a 12vdc powered analog card for the plc and was hoping somebody could help me with this.

I have thought about setting up everything 24vdc and using a 24vdc to 12vdc converter for the radio but thought that this would draw more power. Is this true and does this sound like a good solution?

My 2 cents

Have Two 12 V batteries charged by the solar panel and use both for your 24V and one for your 12V radio.

I agree just use two 12 volt batteries in series, use the negative side for both negatives and pick up off the common point between the two batteries for 12v and pick up off the other side for 24v...
Tom

Thank's for the reply, nice simple solution (seems obvious now)

Should the charging circuit be two 12vdc chargers or one 24vdc charger? Or maybe it doesn't matter.

either or doesnt really matter but to keep things simple i would just use a single 24vdc charger cheers tom

A 24 volt charger is of course the simple solution but if the radio is ran off just one battery then it will more than likely need more of a charge than the other and one charger will then not charge properly. I recomend two chargers.

I am currently using some RTU's from www.IClinks.com that run on 12v. Iam not sure if the requirement for a Automation Direct PLC isa requirement

There is a wide range of DC to Dc Voltage convertors out there with efficency of 90+% to get from 24v dc to 12v dc.
Even poor old Radioshack should have a IC regulator chip to get you to 12v, efficency would be a lot poorer tho

Try Jameco Electronics, they have a good selection of DC to DC converters ranging from 10 watt to 150 watt for $25.00 to $50.00.

I use them for various projects with no problems

Here's one that I used before last year with good results -

DC to DC converter