Hi all,
I am having
12 v,5 amp DC adapter
12v, 7ah lead acid battery
12v SPDT relay
I need circuit diagram for :
when mains fails,circuit should be powered with battery....
12v dc adapter simltaneously charging the battery when mains is ON..
Is it possible with simple SPDT relay ?
Adapter ---> Battery ---> application Circuit
??
Is it OK to put 12v dc adapter to charge the 12v battery permanently?is there risk of battery damage or so?
(deleted)
A bit late to this party, but lead acid gel batteries are pretty tolerant. Although you won't get a full charge, it's OK to float them across a 12V dc supply, to give a sort of ups. I've done that on my wifi router, been like it for a couple of years. Gel batteries are in most burglar alarm systems, outside in the alarm/bell boxes, in extremes of temperature, and last for 12 years or more. Do not use a charger, just use the normal 12Vdc supply to the device, and ensure your battery is charged to the same voltage, in case the device you are powering. is particularly voltage sensitive. Link to Yuasa http://news.yuasa.co.uk/wp-content/uploads/2015/05/NP-Shortform.pdf (other manufacturers are available)
I’ve used this module in a lot of fail-over projects.
I also monitor the input to my projects - to identify when either/both supplies are failing, for an orderly shutdown until power recovers.
raymw:
Lead acid gel batteries are pretty tolerant. Although you won't get a full charge, it's OK to float them across a 12V dc supply, to give a sort of ups.
Sorry, I disagree! 2V per cell is a pretty much discharged cell. You need 2V2 per cell, so 13.2V for a 6 cell lead acid battery. There is a narrow band of voltage either side of 2V2 per cell which is safe to operate in. Too low and the battery will not be fully charged, too high and it will gas and dry out the gel, which will ruin it.
You can just connect the charger, the battery and the load in parallel, you don't need any kind of switching.
Please put a fuse in series with the battery, a lead acid battery can easily supply enough current to start a fire if it is shorted out.
But, the op was not referring to using a battery charger. If the load is small, as in my wifi router, then it'll run quite happily for a few hours on the more or less depleted battery, when the mains supply fails. But, the router will have voltage regulators, and may, for all I know work fine down to 5 or 6 volts. It may not be happy with anything more than 12V. This is not the ideal answer, but it is probably good enough, at no extra cost.
raymw:
But, the op was not referring to using a battery charger. If the load is small, as in my wifi router, then it'll run quite happily for a few hours on the more or less depleted battery, when the mains supply fails. But, the router will have voltage regulators, and may, for all I know work fine down to 5 or 6 volts. It may not be happy with anything more than 12V. This is not the ideal answer, but it is probably good enough, at no extra cost.
The OP stated stated
12 v,5 amp DC adapter
12v, 7ah lead acid battery
Clearly the 12V DC adaptor was to be used as a battery charger. In any case, that slightly misses the point, the point being that if you float a 6 cell lead acid battery at 12V it will always be partially discharged. That in itself is not good for the battery.
The other point is that the comments here are not just for the OP, or you, or me, they are for anyone else who happens to find this discussion and might learn from it.
If you discharge a 6 cell lead acid battery to 5 or 6 volts as you suggest then you will damage it, possibly completely ruin it. Doing so it bad practice and to be avoided if at all possible. If you are happy with that, if it serves your purpose, that's fine, but it's not good practice.
You refer to your load being 'small'. Small is a relative measurement, it doesn't mean anything. If you have a 1000Ah battery then a 10A load is 'small'. If you have a 1Ah battery then a 10A load is far too big.
Just out of interest, we had a one and a half hour power cut on Saturday afternoon. The wifi router carried on without a glitch, the world did not end. So, hopefully, folk reading this thread will learn from it.
Whilst it is correct to float charge around 13.2volts , it is also true a lot of battery backed alarms feed the battery with the output from a 12v regulator and they survive even though it’s incorrect ( my Honeywell Acenta alarm is so made)
I’d agree charger>battery > device.