Does anyone have a simple design for a circuit that will charge a 7Ah 12v gell cell battery? It's for my portable repeater project. I have it 99% done and am at the stage where I'm putting a molex external power connector on it. I need a simple circuit that will charge the battery without overdoing it when connected to a 12 v source.
mancow
Gell Cell battery charger schematic needed
Moderator: Queue Moderator
Presumably you are proposing to use a single fixed-voltage setpoint charger, sometimes known as a float charger, not a smart charger. Putting aside issues about the capacity of such a charger to recharge a storage battery that has been deeply cycled, you can use any charger (or charger design) that would work for a flooded cell. Just be sure that the charger is truly voltage regulated (float charger) and not current regulated (trickle charger).
The critical thing about charging gel cells is to limit the bulk and acceptance stage charging to between 14.1 and 14.3VDC (corrected for temperature variation from 70F), versus a value of about 14.4-14.7VDC for flooded (same correction). This is the basis for the warning not to use a multi-stage (or "smart") charger set for flooded on gels. However, the float voltage for gels is higher than for floodeds; the usually spec'd value is 13.6-13.8VDC (versus 13.2-13.5 for floodeds).
A float charger set for 13.4 or 13.5, therefore, won't cook the gels.
You haven't asked how much power a 7AH battery is worth, or how any battery or bank that is going to be deeply discharged should be recharged, so I'll save those topics for another day.
The critical thing about charging gel cells is to limit the bulk and acceptance stage charging to between 14.1 and 14.3VDC (corrected for temperature variation from 70F), versus a value of about 14.4-14.7VDC for flooded (same correction). This is the basis for the warning not to use a multi-stage (or "smart") charger set for flooded on gels. However, the float voltage for gels is higher than for floodeds; the usually spec'd value is 13.6-13.8VDC (versus 13.2-13.5 for floodeds).
A float charger set for 13.4 or 13.5, therefore, won't cook the gels.
You haven't asked how much power a 7AH battery is worth, or how any battery or bank that is going to be deeply discharged should be recharged, so I'll save those topics for another day.
The unit consisits of two 5 watt portables coupled to a mini duplexer. The audio patch and PTT are routed through a hang timer made from a 555 circuit with its own voltage regulator in a small box. The power for the portables comes from an LM338K regulator fixed at 10 volts. It's connected through a power switch, fuse, and reverse polarity diode circuit and is then connected to the 7Ah gell cell.
I'm basically wanting to set it up so that power could be applied to the molex connector on the panel from a car cigarette lighter adaptor. I would like it to be able to run from the car voltage and also charge the battery or I could put a switch on it to select charge and operate.
I'm trying to get away from having to buy a special stand alone charger unit for it for the sake of ease of use. I have little problem figuring out everything else bur for some reason when it comes to seemingly simple part of the charger system I'm lost.
mancow
I'm basically wanting to set it up so that power could be applied to the molex connector on the panel from a car cigarette lighter adaptor. I would like it to be able to run from the car voltage and also charge the battery or I could put a switch on it to select charge and operate.
I'm trying to get away from having to buy a special stand alone charger unit for it for the sake of ease of use. I have little problem figuring out everything else bur for some reason when it comes to seemingly simple part of the charger system I'm lost.
mancow
I'm a bit confused. If you are powering the radios via the vehicle's electrical system, converting input DC to 10.0VDC for the radios, where does the 7AH battery (which I assume is 12V nominal) come in and why is it needed?
In any event, most vehicle alternator regulators are single voltage set point devices, and the setpoint is usually in the range of 13.5-13.8 VDC. Verify that your cigarette light output is within this range, and, if so, you can safely connect it to a 12V nominal gel cell without problems. This won't do much to recharge a substantially depleted gel cell, but it won't cook it, either.
In any event, most vehicle alternator regulators are single voltage set point devices, and the setpoint is usually in the range of 13.5-13.8 VDC. Verify that your cigarette light output is within this range, and, if so, you can safely connect it to a 12V nominal gel cell without problems. This won't do much to recharge a substantially depleted gel cell, but it won't cook it, either.
What I meant by the vehcile power is that I would like to be able to charge the unit from a car lighter. Also, it would be nice to be able to power the unit from the same car lighter. That way power from the internal battery is not being depleted until the unit is needed and is deployed somewhere.
The unit consists of two BK porables in a box with the circuitry I described. They run on 10v so that's what the regulator was for.
The unit consists of two BK porables in a box with the circuitry I described. They run on 10v so that's what the regulator was for.
Verify that your cigarette light doesn't put out more than 13.8VDC and you won't have a problem cooking a 7AH 12V gel cell. (Be sure it is a gel; most of the 7AH 12V batteries are alarm panel batteries, and many of these are sealed flooded cell.) You might take a look at the size of the wiring running to the cigarette lighter and its fusing, but I doubt you'd see more than 3-4A, and only for a minute or so, if the battery was seriously discharged.