Diode voltage booster settings/achieved voltage (1 Viewer)

[kcjaz]

I just installed an AGM battery and also put in an HKB MK4 (dip switch adjustable). Theoretically each of the 5 dip switches provided +0.2V. With all 5 dip switches on I'm getting about +0.8v boost and 14 to 14.1 volts with hot engine. My X2 AGM wants 14.1v to 14.8v so I'm in the range but just barley. However, I've also read that it may not be good to boost by more than +0.6V (at least the HKB site provides a cryptic statement to this affect).

For those with AGMs and diode voltage boosters, what voltages are you running and how must boost above OEM?

 

[TeCKis300]

This topic is trickier than it appears.

There is not a static voltage to aim for. Charging voltage depends on SOC and temperature. Balancing enough voltage to ensure full charge versus too much voltage where it boils the batts

.6V and over sounds too high IMO. .4V may be all you need.

 

[kcjaz]

This topic is trickier than it appears.

There is not a static voltage to aim for. Charging voltage depends on SOC and temperature. Balancing enough voltage to ensure full charge versus too much voltage where it boils the batts

.6V and over sounds too high IMO. .4V may be all you need.

I realize the voltage isn’t static. I think that’s why the battery data says 14.1 to 14.8.

To me there are two separate considerations. One is what the battery needs to be happy given temp and SOC and whatever else and the other is what the alternator can do while it’s happy.

I’m assuming that if I’m in the battery’s stated range, it’s happy. What I don’t know is if I’m pushing the alternator too hard or if the 14v (+0.8v) may hurt something else.

 

[TeCKis300]

Alternator should be fine. You don't want anywhere near 14.1V on a hot engine. As that'll also mean the batt is warm and will want a lower voltage less it boils the batt.

As the alternator is setup for a lead acid, the diode should be used to compensate for the delta to AGM.

I couldn't find.a bulk charge graphic but this should give you an idea.

 

[gaijin]

I just installed an AGM battery and also put in an HKB MK4 (dip switch adjustable). Theoretically each of the 5 dip switches provided +0.2V. With all 5 dip switches on I'm getting about +0.8v boost and 14 to 14.1 volts with hot engine. My X2 AGM wants 14.1v to 14.8v so I'm in the range but just barley. However, I've also read that it may not be good to boost by more than +0.6V (at least the HKB site provides a cryptic statement to this affect).

For those with AGMs and diode voltage boosters, what voltages are you running and how must boost above OEM?

I would refer you to my post here: AGM Voltage Booster Install

After using this booster for over a year, and monitoring voltage under various conditions (SOC, ambient temp, etc.), I have found that using the booster set on the LOW setting (nominally +0.4-0.5v) provides the best balance of charge without reaching the highest possible charging voltages which may be too much under certain conditions.

Based on your post, I would set your booster to provide +0.4v and then monitor for awhile. OBD Fusion App is great for this.

HTH

 

[kcjaz]

Thanks @gaijin and @TeCKis300, I'm beginning to understand this better. I found the Northstar manual on line which I believe to be the same battery as my X2 SLI27FAGMDP. It has this curve:

the battery also says this on the top:

I think the battery has 6 cells but I'm not 100% sure of that (can't find a spec for this). From the graph at 25C 13.5V/2.275 = 5.9 which is close to 6. I think this graph is also telling me that for a hot engine (>50C) I want the min float charge which would be ~2.175 x 6 = 13v. I think "float" charge is applicable to alternator charging while driving once the battery gets fully charge after starting.

I am now understanding the the +14v numbers are for "cold" in the garage with a charger. I'll back my diode off and monitor.

For reference, here is the Northstar manual.

https://masterbattery.com/wp-content/uploads/2015/05/NorthStar-Automotive-and-Marine-Application-Manual.pdf

 

[kcjaz]

So I just measured voltages with only 1 dip switch (cold engine) and got 14.1 on my meter connected to bat terminals and OBDFusion said 13.9v. Without any boost, it was 13.9 or so at the bat terminals. I'm a bit surprised there is that much difference. Maybe I don't have the right PID point, I'll check that. I'll just monitor and see what it does. I know from watching ODB2 voltage before I installed the diode, it runs 12.9 to 13v hot. What I am wondering now is why do I need the diode if I only need 13V hot (according to the curve) as I seem to be getting near that without it (especially if the OBDII reading is reading low.

 

[grinchy]

I hope you don't plan on underhood temps at 50C. The voltage on the graph for 30C is 13.5v.

Of course I don't recall what the normal underhood temps at the battery location are.

 

[kcjaz]

I hope you don't plan on underhood temps at 50C. The voltage on the graph for 30C is 13.5v.

Of course I don't recall what the normal underhood temps at the battery location are.

50c is 122 F. Doesn’t seem crazy on a 100F ambient day, in bright sun, in a black rig, crawling on a trail or stuck on a freeway. Maybe (hopefully) there is always enough air flow to keep the battery nearer the ambient.

 

[grinchy]

50c is 122 F. Doesn’t seem crazy on a 100F ambient day, in bright sun, in a black rig, crawling on a trail or stuck on a freeway. Maybe (hopefully) there is always enough air flow to keep the battery nearer the ambient.

Sure.but that’s the 99 percent case right? Anyhow, for the three years I was running agm I used a diode and also topped off the battery quarterly or so using a agm charger.

 

[kcjaz]

Set the MK4 with just the first dip switch on and the other 4 off. Drove it the 2 hr drive home from the lake. At 80 mph, I was getting 13.6v on the OBD2. Voltage at bat terminals is 0.1 to 0.2v more at idle so seems like I’m near the upper limit of 13.8v. Ambient was only 79 today. Don’t know what the engine bay battery temp was but when I checked the voltage after the drive home I could put my hands on the battery and it just felt warm so maybe 100F?

At hotter temps the alternator temperature compensation should kick in and drop the voltage right? Seems like it’s set about right (though maybe a tad high) and I didn’t need the adjustable version.