Nice clean wiring. I'm impressed. Well done sir!
Just as our new charger was designed with charging parameters specific to our batteries, in an effort to maximize their lifespan and performance, I'm sure BMW's charging system has been designed in similar fashion. If someone elects to use a battery size or type that is outside of their factory settings, that specific information may need to be updated, in order to maximize the lifespan of that battery.
Jim, while our chargers are designed to maximize the life and performance of our batteries, I certainly don't want to give anyone the impression that they need to buy our charger to maintain our batteries, because that simply isn't the case. I certainly respect your opinion regarding whether a normal automobile charging system is up to the task of maintaining our batteries (or any other batteries designed for deep-cycle use), I just happen to disagree. I also personally disagree with the premise that a vehicle's alternator is only capable of delivering 13.8 volts, as indicated in the sales literature in your link. It does makes for a good sales pitch to sell charge controllers to people though. Ultimately, even the best charger controller is only as good as the wiring connecting it to everything else.
I don't know how long your daily commute is, but if you are running you refrigerator off your battery for 45 hours every week, it probably does make sense to top your battery off with a battery charger every few weeks (it doesn't need to be our charger either). Since you have two isolated batteries in your vehicle, you always have the option of swapping them, if you are concerned about how our battery is performing for auxiliary use.
Teotwaki Jim (too many Jims in this thread ) - I concur with Optima Jim that your alternator should be putting out more than enough voltage and current to fully charge a deep cycle battery of any construction (and any brand). I know my alternator puts out 14.4V steady. Josh measured his at 14.3-14.4v too. What I notice in the picture of your Optima Blue Top is that the guage of the + wire looks rather small. Of the three cables running to the positive terminal, how many are carrying input voltage? Measure the output of your alternator at the stud on the case, then measure the voltage at the + terminal on your Optima. I bet you will see a drop, which may be the reason for the incomplete charging of the battery. As Optima Jim mentioned, your charge time when the engine is running is going to influence the depth of charge, or lack thereof, also. Upsized the input cable (or add another small gauge cable) and that will reduce any voltage drop you may find. FWIW, the charts I find online for voltage drop/distance for various gauges of cable should be taken with a grain of salt (or two). The quality of the cable (alloy of wire) varies greatly, and may not be as conductive as the control wire used for the reference charts. Jump up a size or two to be sure.----------snip-------------
Understood. Couldn't really tell what was under that red cover, as only the small gauge red wire is visible to me in the picture. The voltage measurement should be made not on the load circuit, but at the terminal connection where the charge current is.The small wires to the circuit breakers in the picture that you are referring are output wires for accessories such as the fridge and so on. They are so short that even a high amp draw won't produce a big drop.The main terminals for the battery have mil grade clamps and 2-gauge welding-grade battery cables. They are under the large red and black terminal boots.
I didn't see your post before finishing mine. I am as curious as you about the charge sequence differences between flooded cell and AGM. Just using my analog VM in my Jeep I can see the voltage peak immediately after starting reflecting the higher voltage and current draw in response to the brief, high load discharge from starting the engine. What I think is the issue is the nature of the voltage regulators response to load. Three stage charging is something that is not unique to AGM battery characteristics. Flooded cell batteries also benefit from similar charge profiles. The three stage charger in my camper and the three stage charging that my solar controller employs is not SPECIFICALLY designed for flooded cell or AGM. My suspicion is that AGM batteries have less tolerance of incomplete recharging.Also, as previously mentioned, I've had drives out to Death Valley that should have given plenty of long-term charge time to the Optima. Since pure time does not work it seems that it is more about the charge sequence that AGM batteries prefer. I think that alternator charge systems are designed to maintain wet cell batteries and not AGM types. I have a ScanGuage on my system and I have seen it go to 14.2 volts but it does not do so for the long periods of time that the AGM needs.
:smiley_drive: Just had to chuckle at the above. Classic.Jim,
I spend enough of my time trying to explain to people that they don't need special chargers for our batteries, that releasing our own charger will probably make that task more challenging for me. I do know that it is one of our most-frequently requested products and especially so within certain groups, like Corvette owners. Some people would rather have the guesswork taken out of maintaining their battery and offering our own charger will accomplish that.
---------SNIP---------I don't know how long your daily commute is, so I don't know what ability your charging system has to maintain your batteries. However, by your own estimate, your Optima battery runs your refrigerator for 180 hours every month. To compare the purchase date of your Optima battery and your starting battery and suggest the two applications are comparble in any way is simply not realistic. If you are running an accessory with anyone's battery for 180 hours a month, I would recommend fully-charging the battery periodically with a battery charger, just to make sure it is being properly-maintained. Even if your vehicle's charging system has the ability to properly-maintain the battery, it may not have enough time to do so while you are driving it.