Battery management + battery separator = ??

[DavidR]

I was talking about this to the owner of Equipt outfitters the other day at off-grid expo in denver, he was suggesting a DC to DC charger for vehicles with variable alternators like the ranger. I still don't quite understand how they work, and they're a bit more expensive than typical battery isolators, but supposedly it should do the trick.

edit: Also, you don't want to have the aux battery connected straight, or just off a relay that's otherwise straight to the ranger's main battery. a battery isolator's job is to prioritize the main battery getting charged first and then supply current to the aux as available. if they're both just wired together, and not identical batteries they can get all sorts of screwed up, I'm sure the variable alternator will make that scenario even worse.

I just recently heard about the DC-DC chargers for vehicles like this. I'm also not 100% sure how they work, but my guess is that instead of directly connecting to the truck battery, they provide an active voltage converter that always gives the aux battery a 13.8V charging voltage regardless of the voltage on the truck battery. That would allow the aux battery to fully charge regardless of what voltage the alternator generates in response to the load it sees. It would still need to know when the engine is off so that it can stop charging.

You're right about the cost. The person who told me about them said that good quality ones can cost $700-$800. To be honest, that's why I'm considering some other options even if they are a bit less optimal. I agree that by direct connecting with a relay, there may be some protections of a battery separator that would be sacrificed. Mostly, I think those would be in extreme cases, though, such as if the aux battery has shorted cells or something like that. If both the aux battery and truck battery are healthy, it should be okay to connect them in parallel as long as they are the same chemistry (lead-acid). I made some measurements today, and when the truck decides to charge the main battery, it provides a 13.6V charging voltage. That's a little less than the traditional 13.8V, but I think if the aux battery were charged with 13.6 instead of 13.8, it would be fine. If I do go this route, though, I'd need to make sure the aux battery is in good condition.

There's no doubt that the DC-DC convert is the best possible option, but I might need to wait on it due to the cost.

EDIT: Looks like they're not quite as expensive as I thought. This is the one that was recommended to me. He must have been quoting an installed price:

https://redarcelectronics.com/products/20a-in-vehicle-dc-battery-charger-ignition-control

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[RoadBoss]

I just recently heard about the DC-DC chargers for vehicles like this. I'm also not 100% sure how they work, but my guess is that instead of directly connecting to the truck battery, they provide an active voltage converter that always gives the aux battery a 13.8V charging voltage regardless of the voltage on the truck battery. That would allow the aux battery to fully charge regardless of what voltage the alternator generates in response to the load it sees. It would still need to know when the engine is off so that it can stop charging.

You're right about the cost. The person who told me about them said that good quality ones can cost $700-$800. To be honest, that's why I'm considering some other options even if they are a bit less optimal. I agree that by direct connecting with a relay, there may be some protections of a battery separator that would be sacrificed. Mostly, I think those would be in extreme cases, though, such as if the aux battery has shorted cells or something like that. If both the aux battery and truck battery are healthy, it should be okay to connect them in parallel as long as they are the same chemistry (lead-acid). I made some measurements today, and when the truck decides to charge the main battery, it provides a 13.6V charging voltage. That's a little less than the traditional 13.8V, but I think if the aux battery were charged with 13.6 instead of 13.8, it would be fine. If I do go this route, though, I'd need to make sure the aux battery is in good condition.

There's no doubt that the DC-DC convert is the best possible option, but I might need to wait on it due to the cost.

EDIT: Looks like they're not quite as expensive as I thought. This is the one that was recommended to me. He must have been quoting an installed price:

https://redarcelectronics.com/products/20a-in-vehicle-dc-battery-charger-ignition-control

good info. yeah I've heard tons of people suggest RedArc, also heard good things about Ctek, and National Luna has supposedly just come out with one, though not sure if its available yet.

Also with a quick google search I just found Renogy, which seems to be very affordable, though I don't know anything about them - Amazon reviews are mixed, but you never know if people installed them properly or even used the right product for their application.

anyway, curious to see what you go with. I don't have a camper, but intend to have a decent aux battery setup to run my fridge and some extra power stuff for camping.

 

[t4thfavor]

I have a 100A diode that I'm going to put in a container with a small SLA battery. It won't drain back when the truck battery dies, and the truck battery will still charge it and send current. The radio could still kill the truck battery if something caused it to stick on, but it would likely burn it to the ground before the battery died anyways.

 

[DavidR]

I have a 100A diode that I'm going to put in a container with a small SLA battery. It won't drain back when the truck battery dies, and the truck battery will still charge it and send current. The radio could still kill the truck battery if something caused it to stick on, but it would likely burn it to the ground before the battery died anyways.

That should work. You'll have a slightly bigger drop than with a current source, but the radio has a supply tolerance of 15% so if you use a 100A Schottky diode, you should be within spec as long as the alternator is charging a decent fraction of the time.

 

[Snorebaby]

An update on the battery separator issue. I thought that driving with the headlights on might create enough load that the Ranger would have to charge the battery fairly often, and hence trigger the battery separator, so I drove out to my destination with the lights on, both high and low beams since I have LED headlights. It worked, sort of - the camper battery was fully charged when I arrived. You can probably guess the sort-of part. I forgot to turn the lights on for the drive back today, and the camper's battery dropped below the threshold of the 120V inverter that powers the refrigerator. Without the lights on, the Ranger won't charge its battery enough to keep the camper battery charged through the battery separator. Fortunately, it was on the way back home, so it didn't matter that I arrived with the aux battery almost dead.

I don't really want to be dependent on never forgetting to turn the headlights on during the day, so I'll be trying to figure out how to rig up a relay that triggers off the ignition instead.

Would it work if you had your driving lights on? I don't have the LED headlights but do use the driving light setting. The only time they are not on when the truck is running is when you are in Park.

 

[DavidR]

Would it work if you had your driving lights on? I don't have the LED headlights but do use the driving light setting. The only time they are not on when the truck is running is when you are in Park.

Hi Doug,

Yeah, I did have the daytime lights set to "on". The problem is that the daytime lights use the headlights, which are now LED, so they apparently did not draw enough power to keep the alternator running long enough when I forgot to turn all the headlights on at full power.

I have not replaced the fog lights yet though, they are still halogen, so I searched around for a way to make the daytime driving lights use the fog lights instead of the headlights, but I couldn't find a good solution for that. From searching, I found that other people are also interested in doing that for different reasons, but there doesn't seem to be an easy way to do it.

The long term solution is the DC-DC inverter, but until I'm ready to spend the money for that, I'll just have to remember to manually turn on the headlights or fog lights. On the good side, now that I have forgotten once and ended up with a dead aux battery, I probably won't forget again! Once bitten twice shy

 

[Snorebaby]

Hi Doug,

Yeah, I did have the daytime lights set to "on". The problem is that the daytime lights use the headlights, which are now LED, so they apparently did not draw enough power to keep the alternator running long enough when I forgot to turn all the headlights on at full power.

I have not replaced the fog lights yet though, they are still halogen, so I searched around for a way to make the daytime driving lights use the fog lights instead of the headlights, but I couldn't find a good solution for that. From searching, I found that other people are also interested in doing that for different reasons, but there doesn't seem to be an easy way to do it.

The long term solution is the DC-DC inverter, but until I'm ready to spend the money for that, I'll just have to remember to manually turn on the headlights or fog lights. On the good side, now that I have forgotten once and ended up with a dead aux battery, I probably won't forget again! Once bitten twice shy

Thanks for the reply David. Trying to gather knowledge for possible future endeavors. I have a cargo trailer that has a solar panel to keep the small batteries charged (interior lights and alarm system) when unhooked. I am now wondering when I pull it, should I leave the solar panel plugged in when hooked to the Ranger? My wife's F-150 is a 2013 and doesn't have all the fancy stuff the Ranger does so it should charge the batteries when towed with it. I just recently added the lights/alarm to the trailer.

 

[DavidR]

Thanks for the reply David. Trying to gather knowledge for possible future endeavors. I have a cargo trailer that has a solar panel to keep the small batteries charged (interior lights and alarm system) when unhooked. I am now wondering when I pull it, should I leave the solar panel plugged in when hooked to the Ranger? My wife's F-150 is a 2013 and doesn't have all the fancy stuff the Ranger does so it should charge the batteries when towed with it. I just recently added the lights/alarm to the trailer.

It's a good question. It sounds like you already have a battery management unit that supports having both the solar panel and the tow vehicle connected, but it's an older system that works with the '13 F-150 and might not work with the Ranger, similar to what we have in our camper. If you want to do that with the Ranger, you'll probably need a DC-DC inverter that also has an input for the solar panel. Redarc does make one like that, but it's about $50 more than the one that doesn't have the solar panel input.

 

[Snorebaby]

It's a good question. It sounds like you already have a battery management unit that supports having both the solar panel and the tow vehicle connected, but it's an older system that works with the '13 F-150 and might not work with the Ranger, similar to what we have in our camper. If you want to do that with the Ranger, you'll probably need a DC-DC inverter that also has an input for the solar panel. Redarc does make one like that, but it's about $50 more than the one that doesn't have the solar panel input.

Don't have a battery management system...unless you count me unplugging the solar panel .

It is a 12v car alarm and the inside lights are 12v LED strip lights. It is using 3 12v 5amp batteries for power that is maintained by the solar panel when not hooked to the truck. The F-150 doesn't have the battery management system the Ranger has (from what I have been reading). So I assume the F-150 sends full alternator voltage to the trailer and the Ranger manages the output of the alternator based on needs. The trailer lights are also LED. So I was thinking I could unplug the solar panel when pulling with the F-150 and have to keep the panel plugged in when pulling with the Ranger to maintain charging voltage to the 3 batteries. Am I correct in this thinking?

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