1996 Windstar Not Charge

I have a 1996 Ford Windstar, Monday the radio stopped working and then 5 minutes later the engine light started blinking, then I had to keep my foot on the gas pedal just to keep it running, then that didn't help. I replaced the alternator Monday night and the battery Tuesday morning. My daughter drove it to school (a half an hour away), it did just fine, but on her way home (after driving it for 15 minutes) it started doing the same thing. I had the alternator and the battery tested and they are ok. But it won't keep charged. I can't figure this out.

Thanks
davebower1

Since your alternator and battery are fine I would look for fuses in the charging circuit that might be blown or something draining the battery while it is parked. An easy way to test for drain is to remove a battery cable while the van is off and use an ammeter to measure the current draw. There will be milliamps for memorys etc but anything more than a few a few hundred milliamps should be of interest. You can then pull fuses one by one to see what circuit is drawing excessive current.

Dave
A quick test of charging system is this. Disconnect the battery cable while the van is running. If the van dies then proceed further. The van should run try and increase the rpm to about 1500 or 2000 and try again. Check fuses, loose wires, loose battery cable, bad ground. A test with a voltmeter across the positive and negative terminals while running should be about 14.7 volts. Also do you have any problems starting? The ignition switch could be going bad. Make checks and report back. I actually got a bad alternator it was charging intermittenley. Brought it to Sears as that is where I bought the battery and they put it on the tester and discovered the problem. The Alternator was 6 months old. I got a new one for free from CarQuest and new battery from Sears for free. Where did you get your battery and alternator from?