Just trying to get an idea of how long a distributor equipped car will run total loss on a small 12v battery before needing to be charged. I do not intend to install a mag or coils, just looking to select a proper sized battery to last more than a day of touring. It is simple and cheap enough to simply recharge at the end the day. No starter either, just running the ignition. Also I never stay out past dark so lights wont factor in here either. Thanks guys
Depends on how "small" you're thinking..dimensionally speaking. I'd use one of those marine type starting/deep cycle batteries. They hold up well.
David, I have been running my 24 truck on a 6v battery for several years. I have been on day-long tours of 100 miles where we left about an hour before sun up, made several stops and starts (using the starter) and arrived home around dark, and was still running nicely and able to start with the starter. I used the lights until the sun came up, and again before we got home, brake light all day and several starts with the starter. Sometimes I have parked it without putting the charger on and then took it on another tour. I can usually drive it on several tours before it needs a recharge.
I was thinking of lawn tractor battery for its small size, low cost as discharging and recharging would likely kill it in one season. It will be held in a small toolbox on the car. I dont really want to get into expensive and very large and heavy batteries. I also dont want to get into speciality batteries. I think most small batteries are under 300 cca, how many miles dont you think a distributor will run on that?
I'd carry a backup battery and drive till the first one fails to get an idea of how long it will last. Different distributor ignition systems will vary in amp hour consumption so making an accurate prediction is not really feasible.
Actually is is very feasable to just measure it. Put an ammeter in series with the battery used for the ignition and go for a drive. Measure the discharge current in amperes and then get the amp hour rating on the battery you intend to use. If the ignition is drawing say 2 amps while you are running then a 20 amp hour battery is going to be dead in 10 hours of running but you should probably recharge it in half that time so as not to deeply discharge the battery since that has a lot to do with battery total life expectancy. Since you have no charging system at all and I assume you have a brake light too then I would go for a regular size car battery (Group 1 size) and ask what the amp hour capacity is. CCA is of no value here at all since your T is not a hard motor to crank over and most of the discharge will be the ignition since it is constant. You might want to make sure you have the right size ballast resistor to be used with your coil since that could have an effect on the DC drain. If you have the wrong value or no resistor when there in fact should be one it could make a big difference in battery life and charge times. Use an accurate analog ammeter for your measurement.
John, I considered using the amp draw vs battery capacity but thought that would be misleading as it would not be possible to know at what level of discharge the battery would still have power enough to keep the motor running. OK the procedure is feasible but the results will not accurately predict when the engine will no longer run.
Certainly John can answer this better but, I was thinking along the same lines as yourself. If the battery will be dead in 10 hours, as in John's hypothetical story, you can probably bet that at 9 hours there wouldn't be enough charge to run the car anyway. So, in other words, you don't want to know so much when the battery will be dead, as you do how much useful time it will put out. OR, is THAT what the amp-hour rating is really telling us?
David, I have run for better than a week on a full size car battery. Get one that fits the battery box and have fun. Scott
I think Johns point about not using a battery until it is completely dead is very important. If you want any kind of life out of the battery, don't get one thats to small, and recharge it after every use.
Erich - A very good point that John made, and that you have emphisized.
There are those that drive on battery exclusively, and just top off the battery occasionally with a battery charger as David Mazza has suggested. I think that a permanent set-up like David Mazza is talking about, is a good candidate for a deep-cycle battery, as this kind of use is what a deep-cycle battery is designed for. A normal "starting battery" is designed to be kept fully charged at all times. FWIW,....harold
The previous owner of my 14 deleted the mag, added a starter and a dizzy. He did install a battery carrier in the "usual" place in which I have a full size 6 volt battery. I have run several multi-day tours without daily charging with no problem. After the tour I would test the battery and was still holding a good charge. I have been thinking of utilizing an inexpensive HF solar panel to trickle charge the battery while driving. They are 12 volt and put out 1.5 watts. I bought a DC to DC controller with a pot that I can reduce the output to a little over 6 volts. John: I would be interested in your opinion as to whether this would be of any benefit---this is the same car you have helped me with. I am also going to do an ammeter test as you described.
This is great info, also a good idea for using a deep cycle bat. I always get multiple days from one with my trolling motor. I will try to find out amp draw for a dist, I dont really think it would be very much. This system may not be for everyone but it seems to reliable and inexpensive for some model t people. Would the distributor system draw more or less than a good condition coils and timer?
While the Ford coil is buzzing, it should draw about 1.3 amps. A typical distributor from a 6 volt VW draws about 2 amps. If you want to run for 10 hours with good reliability, I would recommend about twice the total needed capacity. In my example two times 2 amps times 10 hour would be 40 ampere hours. I think your first guess of a lawn mower tractor battery would work.
The term CCA means Cold Cranking Amperes, for a typical modern vehicle it needs to be 400 to 700 amperes.