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Battery Isolator Operation
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Author:  whemme [ Thu Nov 26, 2020 8:03 pm ]
Post subject:  Battery Isolator Operation

The battery isolator in your born Free is most likely a Sure Power P/N 1602. You will find it attached to the inside of the E350's and E450's frame rail around the area under the driver's seat. You will have to slide under your coach in order to see it attached with 8 screws. It is a 3 terminal device. The attached center photo is a schematic diagram of the isolator that shows terminals 1 and 2 are reverse diode isolated from terminal A. The bottom attached schematic does not show the separate voltage regulator connection to the chassis alternator, the voltage regulator is built into the Ford alternator.

The whole purpose of this isolator is to permit the chassis alternator to charge your house batteries while driving the coach. However, when the chassis engine is not running, the isolator opens the connection between the chassis battery and the house batteries so that no current from the house batteries flows forward to any chassis functions.

How this works is that the coach's alternator output is connected to center A terminal. Then the isolator's terminal 1 is connected back to your chassis battery and also your alternator's voltage regulator. The isolator's terminal 2 is connected to your house batteries. In normal operation when your chassis engine is started, the alternator output connected to terminal A gets feed back to the chassis battery and the alternator's voltage regulator via terminal 1. Since the chassis battery voltage is feeding the alternator's voltage regulator, the voltage regulator will typically set the alternator's charge voltage output to the +13.5 to 14.5 vdc range. This same charge voltage is feed to your house batteries via terminal 2.

Two possible different failures can happen to this isolator. Failure #1 would be if the isolator's terminal 1 output fails, no charging voltage gets to the chassis battery but worse the alternator's voltage regulator seeing no charge voltage cranks up the alternator voltage to the maximum +18.0 vdc available thus causing your house batteries to start boiling acid - this will destruct your house batteries quickly. But also with no charge voltage available on terminal 1, the chassis battery will no longer be receiving a charge and will eventually discharge.

Failure #2 would be if the isolator's terminal 2 output fails, no charging voltage will then get to the house batteries. They normally get charged while driving the coach but not if terminal 2 output fails.

You can buy a new Sure Power 1602 from several sources on the internet. The least expensive I found was $67.05 from the following source by clicking on the link below.

https://allbatterysalesandservice.com/s ... utput-1602

Attachments:
Sure Power PN 201602 Battery Isolator.jpg
Sure Power PN 201602 Battery Isolator.jpg [ 106.93 KiB | Viewed 435 times ]
Sure Power PN 1602 Battery Isolator Schematic.png
Sure Power PN 1602 Battery Isolator Schematic.png [ 28.19 KiB | Viewed 435 times ]
Screen Shot 2020-11-26 at 7.34.47 PM.png
Screen Shot 2020-11-26 at 7.34.47 PM.png [ 69.35 KiB | Viewed 435 times ]

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