This is not an immediate disaster for disposable batteries, but for rechargeable batteries you will dramatically shorten the life of the battery as well as its ability to recharge. The 6 volt battery should be disconnected by now, but the circuit is being kept alive by the larger 12 volt unit as the smaller battery continues to drain, moving far below its design capabilities. Meaning the total voltage being supplied is 17.6 volts (5 volts + 12.6 volts). Our smaller 6 volt battery as it drains might drop to 5 volts, but the 12 volt battery (which is actually in this example 12.6 volts) still has enough charge.
In our example, we are powering an 18 volt device, which may have a cut off at 16 volts. In fact, if you look closely at some manufacturers who claim their battery will last for thousands of cycles, they clearly state something along the lines of “when discharged to 80% State of Charge”. These built in cut-off points are there because batteries have a shorter life if they are run completely flat each time. Its one reason why the ignition lights in a car might turn on, but the starter motor wants nothing to do with you. When this voltage drops in a device below a certain point, the auto cut-off may engage, switching off the item or causing it to refuse to operate. As batteries discharge, their voltage drops. Dischargingĭuring discharge the weaker battery will run flat first. The real problems arise during discharging and recharging cycles (if the batteries are rechargeable). If you were to connect a device to the battery bank it is capable of powering (say a 0.5 amp bulb) then it would work. Not a disaster if you were only expecting 5 Ah, at least not a problem right away. In the example above, this would be the 5.2 Ah battery. The first practical outcome is that the amp hour capacity will be the lowest of the batteries connected together. A flooded lead acid battery may have different discharge and recharge patterns compared to a sealed lead acid battery. For more on this subject see Which deep cycle ah battery.įurthermore, these ratings and behaviors can be different depending on the structure of the battery. Some manufacturers will claim their battery is 5 Ah using the “20 hour rating”, while others will say their battery is 5 Ah using the “100 hour rating”. You also need to check with the manufacturer on how they arrived at their amp hour rating, because different manufacturers use different methods – not all 5 Ah batteries are 5 Ah in the way you might think. Amp hour ratings are also much harder to test without accurately discharging both units at the same rate under the same conditions and accurately measuring the results. The 6 volt battery might really be a 5.2 Ah, while the 12 volt battery might be 5.5 Ah. Matching amp hour ratings is much more difficult. This can however be fairly easy to read with a volt meter if one was to check.
A 6 volt battery might have a cell voltage of 2.2 volts and a 12 volt battery might have a cell voltage of 2.1 volts. Individual cell voltages differ, even with batteries of the same brand and manufacturer. The reality is that no 6 volt battery is exactly 6 volts and no 12 volt battery is exactly 12 volts. Therefore, all you have done is connected nine 2 volt cells together to get 18 volts … so what’s the problem? A 6 volt battery is often three 2 volt cells and a 12 volt battery is usually six 2 volt cells.
48V BATTERY METER WIRING DIAGRAM SERIES
In theory, a 6 volt 5 Ah battery and a 12 volt 5 Ah battery connected in series will give a supply of 18 volts (6 volts + 12 volts) and 5 Ah. This is where most tutorials end, but what happens if you wire batteries of different voltages and amp hour capacities together? Most people simply answer by telling you “Don’t do it!” … but why not? Connecting batteries of different voltages in series
As in the diagram above, two 6 volt 4.5 ah batteries wired in series are capable of providing 12 volts (6 volts + 6 volts) and 4.5 amp hours. The basic concept when connecting in series is that you add the voltages of the batteries together, but the amp hour capacity remains the same. Connecting in series increases voltage only For more information on wiring in parallel see Connecting batteries in parallel or our article on building battery banks. This article deals with issues surrounding wiring in series (i.e. Different wiring configurations give us different voltages or amp hour capacities. In the graphics we’ve used sealed lead acid batteries but the concepts of how units are connected is true of all battery types.
The illustrations below show how these set wiring variations can produce different voltage and amp hour outputs. There are two ways to wire batteries together, parallel and series.