Rowls1958
Free Member
- Aug 9, 2023
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- 2
- Funster No
- 97,989
- MH
- Hymer Free S 600
I saw this post from Martin Bushnell at A and N Caravan Services. I understand he is a well respected engineer and basically he says that in a modern van with stop/start technology, if it has an AGM van battery you must use an AGM leisure battery ??
AGM batteries are designed for use with Stop/Start engines.
The very nature of their build, is that when charging at high currents, typically 120 to 180Amps and discharging in short bursts every time the engine is restarted the plates can't buckle due to the use of Glass Matt into which the dielectric is absorbed creating a physical barrier between the plates. Unlike a conventional battery that has a Wet or Gel substance as the dielectric which can't stop physical damage if heavily charged or discharged.
In a "conventional" battery and we can include the EFB (enhanced flooded battery) range of products, the battery uses thermal convection to assist in cooling the dielectric as it charges at a relatively low current, which in a Motorhome or Touring Caravan is usually between 15 to 30Amps. When an AGM battery is charged in this manner the heat can't be dispersed so can cause the pressure to build up to the point of splitting the case. When an AGM battery is used as a vehicle (starter) battery for an engine which uses Stop/Start technology its charge and discharge time is insufficient for the heat to build up.
AGM batteries require a higher charge voltage due to the makeup of the dielectric, typically 2.47 to 2.49 volts per cell so a six cell nominally 12volt battery will need an absorption voltage of between 14.82 and 14.94 volts to obtain a full charge. As batteries of different technologies, requiring different voltages, can't be charged from the same source a vehicle that is fitted with a Stop/Start engine and an AGM vehicle battery can only have an AGM battery for the habitation services. Not ideal and AGM batteries tend to fail prematurely. Most chargers that have an AGM setting will either only charge at the absorption rate of a short period, typically one hour or will have a temperature sensor that must be attached to the battery for proper use. This will almost always result in the habitation battery never reaching full capacity. In most installations the habitation battery is charged from the alternator when the engine is running by use of a split charge circuit. If the alternator is designed to charge Lead technology batteries it will be putting out 14.2 to 14.4 volts so the AGM battery which will be connected in parallel with the vehicle battery will be constantly undercharged.
In short, we don't recommend the use of AGM batteries for habitation use unless the vehicle has a Stop/Start engine and is fitted with an AGM starter battery and an AGM compliant mains charger.
AGM batteries are designed for use with Stop/Start engines.
The very nature of their build, is that when charging at high currents, typically 120 to 180Amps and discharging in short bursts every time the engine is restarted the plates can't buckle due to the use of Glass Matt into which the dielectric is absorbed creating a physical barrier between the plates. Unlike a conventional battery that has a Wet or Gel substance as the dielectric which can't stop physical damage if heavily charged or discharged.
In a "conventional" battery and we can include the EFB (enhanced flooded battery) range of products, the battery uses thermal convection to assist in cooling the dielectric as it charges at a relatively low current, which in a Motorhome or Touring Caravan is usually between 15 to 30Amps. When an AGM battery is charged in this manner the heat can't be dispersed so can cause the pressure to build up to the point of splitting the case. When an AGM battery is used as a vehicle (starter) battery for an engine which uses Stop/Start technology its charge and discharge time is insufficient for the heat to build up.
AGM batteries require a higher charge voltage due to the makeup of the dielectric, typically 2.47 to 2.49 volts per cell so a six cell nominally 12volt battery will need an absorption voltage of between 14.82 and 14.94 volts to obtain a full charge. As batteries of different technologies, requiring different voltages, can't be charged from the same source a vehicle that is fitted with a Stop/Start engine and an AGM vehicle battery can only have an AGM battery for the habitation services. Not ideal and AGM batteries tend to fail prematurely. Most chargers that have an AGM setting will either only charge at the absorption rate of a short period, typically one hour or will have a temperature sensor that must be attached to the battery for proper use. This will almost always result in the habitation battery never reaching full capacity. In most installations the habitation battery is charged from the alternator when the engine is running by use of a split charge circuit. If the alternator is designed to charge Lead technology batteries it will be putting out 14.2 to 14.4 volts so the AGM battery which will be connected in parallel with the vehicle battery will be constantly undercharged.
In short, we don't recommend the use of AGM batteries for habitation use unless the vehicle has a Stop/Start engine and is fitted with an AGM starter battery and an AGM compliant mains charger.