Battery Separators for Campers and Vans

Battery Separator Review: SurePower 1314a vs Blue Seas SI-ACR

Perhaps the most important function of your camping vehicles electrical system is its ability to charge your batteries with the vehicle alternator. For me, this seems to be the charging source that is most used for keeping my camper batteries charged. The idea is to use a relay to connect the camper (house) battery to the starting battery so the alternator charges both while the engine is running. When the engine is off the relay separates the starting battery from the house, attempting to preserve 100% of the starting battery capacity for engine cranking. There are a few different relays available. I also use a solar panel to charge my batteries. The solar panel adds to the complexity of the proccess. There are at least a few different methods/gadgets to make it work together.

Old School Method
The old school way is to use a Continuous Duty Solenoid (relay). To set this up, first you connect the positive connections of both batteries to either side of the relay. Then you send power (from a source that is only hot when the vehicle is running) to the relay switch which electronically  to connects the two banks. This a good way to go, simple and it is predictable.

If you are using solar panels on the house batteries with this method there should be no problems. The panels and alternator will charge  both banks  when the engine is running (this is not a problem). When the engine is off, the panels only charge the house batteries. So solar panels do not affect the function of this system.

There is one problem with this method. Whenever you start the vehicle, both battery banks are being used to crank the engine. This wears on all parts of the connection system, steals valuable amp hours from the house battery and causes a voltage drop/surge on the house electrical system. There is also a chance that if  one of the battery banks is severely discharged (most likely the house battery) it will steal all the voltage and possibly leave the starting battery uncharged (although this is probably a  rare occurrence in reality). Perhaps if you are doing a lot of starting and stopping the alternator doesn’t have a chance to charge much and you end up basically equalizing both batteries to an uncharged state.

Of course in the age of electronics there are now “smart” relays or “Separators” available that are able to read voltages from one or both banks and can charge them individually if they are low.

SurePower 1314a

The  SurePower 1314 A is battery separator that was widly used and came installed in  Four Wheel campers before 2015. The  SurePower 1314A (unidirectional) is a 100A battery separator module with an integrated relay for 12V systems. If the main battery is above the connect threshold, the relay connects the two banks together. If the main battery is below the disconnect threshold the unit will open the relay. The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the charging system is operating. This will cause the relay to close and the charging system can charge both banks of batteries. The disconnect voltage is set to a nominal 12.7V, which is near the full charge resting voltage of the batteries. This will cause the relay to be opened shortly after the engine is stopped, att
empting to preserve 100% of the starting battery capacity for engine cranking. An optional start override is also available. When the engine is started, the start signal causes the controller to check if the auxiliary battery is within about 1V of the main battery; if so, the relay contact is closed; thus, providing the starter system with maximum battery voltage available.

This device works great when used in conjunctin with solar panels charging the house battery. This device is a unidirectional sensing relay. What that means is that it only senses voltage on one side of the device, ideally the starting battery side. Although the one sided feature initially seems like a downgrade, it actually greatly simplifies your solar charging system. When the vehicle is started, only the starting battery is used and there is a time delay until the banks are connected for alternator charging. This takes the strain of starting off of the house system. If you are using Solar Panels on your Four Wheel Camper I think this is the device to use, because of its uni-directional function.

Sure Power(now Bussmann) Makes a bidirectional sensing unit (1315) which I think is less prefered when used with a solar charging system. These units come in 100 and 150 amp capacities.

If there is a down side to this device I would say that there have been quite a few reports of failing units. Although there alot of them out there working fine so I guess your mileage will vary. Another slight negative is that it draws about 1 amp which is 50% more draw than its more modern competition, the Blue Sea ACR.

Blue Sea Systems SI-ACR

One of the newest devices to come on the market for battery separation is the Blue Sea Systems SI-ACR. Seems as if this is the device being install on 2015 and newer Four Wheel Campers. This device senses voltage on both sides so if you are using it with a Solar charging system, you have a complication. Since this device will keep the battery banks connected whenever it is sunny out, your house batteries be used to start the vehecle, not desirable for reason stated above…This is where the SI feature comes in.

The SI stands for start Isolation. To use this feature you send a 12v starting signal to the ACR and it instantly disconnecth the banks separating the house battery from the starter battery. The hard part is finding a hot starting signal. This is going to be tough to get on a FourWheel Camper. On a Sprinter Conversion it is pretty easy to get to the starter to attach a  wire to the posative terminal  and run it to the acr SI terminal.

Here is a picture  of the Starter with the SI wire attached from under my Van.