Post by tonyb on Oct 31, 2016 9:59:02 GMT
Contributions from Graham, Tonyqj & Telemachus
Such meters usually have 5 or 6 display modes:
1. Amps
2. Volts
3. Amp hours into the battery (but note this - NOT Amp hours actually converted into chemical energy and stored within the battery)
4. Amp hours out of the battery
5. percentage of charge
6. and finally maybe time left before charging (or time left until flat)
In the case of the first two (Amps & Volts) they are accurate so would agree with an ammeter and voltmeter or a multi-meter. Just because these two are accurate however does not mean the others are. Although pure Amp hours in and Amp hours out will be accurate they are somewhat problematical, and as for the percentage of charge and time left they are often a work of fiction.
The percentage of the Amp hours into a battery that is converted to stored chemical energy alters hour to hour and day to day as the temperature, charging voltage, and battery condition but it will NEVER be 100%. It will also vary from battery type/design to battery type. Just to substantiate this feel some batteries that have been on charge for a while, they will be warm or hot. Where did this heat come from? The answer is the charging electricity so from that you can deduce that some charge went to make heat, not convert chemicals. Batteries that are on charge tend to vent hydrogen and oxygen so once again the question is where did the energy come form to break down the electrolyte? The answer is still the chargr. Just to complicate things further the actual capacity of the battery reduces over time means that the meter can not know how much electricity is actually stored in the battery - even if it is 100% charged. Within days or at the most a few weeks it WILL be less that the number on the label.
The upshot of the above paragraph is that any display that results from Amp hour counting will over record the amount of charge put into the battery and once that is wrong the percentage of charge and time left must also be wrong.
The makers try to compensate for this by putting "fiddle factors" into the algorithms the gauges use to work out the percentage charge and time left.
If you have understood some of the topics that are around concerning battery charging you will know that when the charging current drops to a very low level - often quoted as 1% of bank capacity - the battery can be CONSIDERED as fully charged. It probably won't be but it will be near enough for practical use. The meterβs electronics knows this and at that point resets itself to 100% charged. All that sounds fine and dandy but the meters are not usually set at 1% by the factory. Probably more like 2% to 4% so they resynchronise early. This causes them to overstate the degree of charge and that in turn persuades many boaters to destroy their batteries by constant and ongoing undercharging. The problems get worse if users do not continue charging until the current drops to such a low percentage. This is why solar charging has such advantages, it provides many hours at a low charge rate to get the final few percentage of charge back in.
Some advocate continuing charging at 14 to 14.5 volts until the charging current fails to fall for at least 30 minutes.
If you really understand the limitations in such meters, reset them to synchronise at a very low percentage (known as tail current) AND very regularly charge for long enough to cause them to resynchronise then they will be fairly accurate on all scales. If you do not all you can rely upon is the amps and volts. Even so as the battery capacity will have dropped over time the percentage of charge and the time left might still be incorrect.
A rather major point of confusion relates to charging with "intelligent" multi-stage battery chargers. They are not very good at getting the point at which the drop into float correct. (see the battery charging advice topic). All too often they drop to float far too early and at that point the reduced charging voltage will make it look as if the tail current has stabilised. The majority of engine alternators do not drop to float so will no try to confuse you in this way. If using tail current from a battery charger turn if off for a short time and back on again to make sure it is charging at around 14 to 14.5 volts. Better still disable adaptive charging and use it like an engine alternator so you turn it off when the tail current stops falling.
Once you have resynchronised the meter you can note the Amp hours out and percentage of charge and calculate the current capacity of the bank. e.g. 50Ah out that takes it to 75% of charge tells you the battery bank capacity is 200Ah because 50Ah is 1/4 of the bank capacity.
Such meters usually have 5 or 6 display modes:
1. Amps
2. Volts
3. Amp hours into the battery (but note this - NOT Amp hours actually converted into chemical energy and stored within the battery)
4. Amp hours out of the battery
5. percentage of charge
6. and finally maybe time left before charging (or time left until flat)
In the case of the first two (Amps & Volts) they are accurate so would agree with an ammeter and voltmeter or a multi-meter. Just because these two are accurate however does not mean the others are. Although pure Amp hours in and Amp hours out will be accurate they are somewhat problematical, and as for the percentage of charge and time left they are often a work of fiction.
The percentage of the Amp hours into a battery that is converted to stored chemical energy alters hour to hour and day to day as the temperature, charging voltage, and battery condition but it will NEVER be 100%. It will also vary from battery type/design to battery type. Just to substantiate this feel some batteries that have been on charge for a while, they will be warm or hot. Where did this heat come from? The answer is the charging electricity so from that you can deduce that some charge went to make heat, not convert chemicals. Batteries that are on charge tend to vent hydrogen and oxygen so once again the question is where did the energy come form to break down the electrolyte? The answer is still the chargr. Just to complicate things further the actual capacity of the battery reduces over time means that the meter can not know how much electricity is actually stored in the battery - even if it is 100% charged. Within days or at the most a few weeks it WILL be less that the number on the label.
The upshot of the above paragraph is that any display that results from Amp hour counting will over record the amount of charge put into the battery and once that is wrong the percentage of charge and time left must also be wrong.
The makers try to compensate for this by putting "fiddle factors" into the algorithms the gauges use to work out the percentage charge and time left.
If you have understood some of the topics that are around concerning battery charging you will know that when the charging current drops to a very low level - often quoted as 1% of bank capacity - the battery can be CONSIDERED as fully charged. It probably won't be but it will be near enough for practical use. The meterβs electronics knows this and at that point resets itself to 100% charged. All that sounds fine and dandy but the meters are not usually set at 1% by the factory. Probably more like 2% to 4% so they resynchronise early. This causes them to overstate the degree of charge and that in turn persuades many boaters to destroy their batteries by constant and ongoing undercharging. The problems get worse if users do not continue charging until the current drops to such a low percentage. This is why solar charging has such advantages, it provides many hours at a low charge rate to get the final few percentage of charge back in.
Some advocate continuing charging at 14 to 14.5 volts until the charging current fails to fall for at least 30 minutes.
If you really understand the limitations in such meters, reset them to synchronise at a very low percentage (known as tail current) AND very regularly charge for long enough to cause them to resynchronise then they will be fairly accurate on all scales. If you do not all you can rely upon is the amps and volts. Even so as the battery capacity will have dropped over time the percentage of charge and the time left might still be incorrect.
A rather major point of confusion relates to charging with "intelligent" multi-stage battery chargers. They are not very good at getting the point at which the drop into float correct. (see the battery charging advice topic). All too often they drop to float far too early and at that point the reduced charging voltage will make it look as if the tail current has stabilised. The majority of engine alternators do not drop to float so will no try to confuse you in this way. If using tail current from a battery charger turn if off for a short time and back on again to make sure it is charging at around 14 to 14.5 volts. Better still disable adaptive charging and use it like an engine alternator so you turn it off when the tail current stops falling.
Once you have resynchronised the meter you can note the Amp hours out and percentage of charge and calculate the current capacity of the bank. e.g. 50Ah out that takes it to 75% of charge tells you the battery bank capacity is 200Ah because 50Ah is 1/4 of the bank capacity.