DC to DC charger or solar instead?

spressomon

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^ The Sterling and Victron seem to differ in this regard. The priority with the Sterling is always the starting/house battery/batteries (2-starting batteries on my HD2500). Once the starting battery's voltage reaches 13.2v (not sure how it knows if the alternator is sending higher voltage than 13.2v...but this is how Sterling explains it in their op manual) it allows the BB1260 (ditto for their BB1230, et al) to then send up to 70A of current to the auxiliary battery.
 

e9999

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It charges the auxiliary battery first then the starting battery. I think the starting battery charges at the same time just like normal, but the the dcdc charger charges each battery to higher volt. For instance, let’s say both batteries are optima and really want to be charged to 15V. The starter battery would recharge to the standard voltage that the alternator can do having nothing to do with the dcdc charger or auxiliary battery. Then once the auxiliary battery is topped up to 15V, the dcdc charger switches back to the starter battery and tops it off to 15V. The alternator is not capable of the 15v charge on its own, but it can recharge the starter battery to 14.6 or whatever it was originally designed for.
that's interesting. Convoluted, but a relatively easy way to get the starter battery charged to a higher voltage than the alternator can deliver. Although the odd thing about this is that the charged aux battery would then see its voltage decrease when it charges the starter battery and would need to be charged yet again. And then the starter battery and then etc etc...
 

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^ The Sterling and Victron seem to differ in this regard. The priority with the Sterling is always the starting/house battery/batteries (2-starting batteries on my HD2500). Once the starting battery's voltage reaches 13.2v (not sure how it knows if the alternator is sending higher voltage than 13.2v...but this is how Sterling explains it in their op manual) it allows the BB1260 (ditto for their BB1230, et al) to then send up to 70A of current to the auxiliary battery.
13.2V may not yet be a fully-charged FLA starter battery if it's going up rather than coming down from a peak, but they probably figure that it's high enough to ensure at least one start, and so that it's time to get going on the aux battery.
Although what the voltage can be would depend greatly on how powerful the alternator is, of course.
 

spressomon

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^ After our maiden voyage with approximately 4,000 miles the entire system worked as expected and properly. I doubt, but can't confirm as I haven't had time to verify current flow, if all current flows to the BB1260 (and thus the auxiliary battery) when house battery is 13.2v or higher...
 

e9999

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^
if the DC2DC is wired downstream from the starter battery, the starter battery would have to be fully charged and not accepting any more current for that to happen at that point... Unlikely, I would think. But, of course, when the starter battery is finally fully charged, then, yes, most of the current would go to the DC2DC if there is a load on it sucking power.
 
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So I’ve circled back around to my initial idea which is the victron blue solar 100/15 and a simple voltage sensitive relay to automatically connect and disconnect the second battery. I will almost certainly get a redarc bcdc1225d in the future, but will do that for my 200 series and probably use a portable battery box like kickass sells with the dcdc charger mounted right on the box. This way it is portable and much more convenient and versatile. I already have my dual batteries mounted in my 100 engine bay so that’s why i decided to go the cheaper and simpler route on this vehicle.

I think the last question I have on the victron setup is: do I just connect the starter battery to the “batt” connection and the house battery to the “load” connection? I believe by doing that, I have over charge protection for both batteries. Just a reminder, my solar panel will be permanently mounted on the hood in Houston, so overcharge could be a real issue.
 

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^ My gut feeling is that the load output is not intended for charging of a second battery, more like lights etc. But what you propose would take care fine of the charging of the starter battery at least, I imagine. And you may be able to use the load side creatively. I don't remember how the Victron operates but I doubt that you'd have separate control of voltage algorithm for the load side. I'm guessing it just connects or not the load to the charging battery, with an adjustable low voltage disconnect. There is probably also an overcurrent disconnect on the load side, presumably at 15A. So, if it's indeed just a connection between the 2 sides, then the battery on the load side would always see the same voltage as the starter battery, aside from wiring losses. Which may be fine for charging if they are the same type. And you would not have to worry about overvoltage. But if they are different batteries, that may not work well if they need different charging schemes. Another issue I'd check is what would happen if you put a very discharged load battery together with a very charged starter battery, as in is it possible that if the load battery would normally suck in more than 15A the load side would disconnect and it would never get charged? (Not an issue if they start at reasonably close levels I suppose.) Then again, I may be completely wrong about all of the above. Somebody will know.

I suggest you ask Victron directly if you are not sure. They responded to an email inquiry of mine within a day and were quite helpful. They are in Holland IIRC, and seem very professional.
 
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Sounds like a plan. I’ll email them tonight or tomorrow and see what they say and will report back here with the answer. Unless they say differently, I will have a red top optima for starting and yellow top for house so the demands should be the same. Thanks.
 

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Yup, let us know what you find out, this is interesting stuff...
 
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That looks about how I was planning and I think that looks great, thanks for posting the pics. I am hoping to have the hood mounted panel be 120W so I don’t have to carry around a larger folding panel. I may have to supplement at a later time with a larger folding panel, but I’m just hoping this setup works out.

Victron emailed back saying I cannot connect the auxiliary battery to the load connection and referred me to contact a local dealer for their Cyrix battery combiner. Looks like it’s basically an isolator, but maybe it “smarter” than just that. I emailed a local rep and forwarded him Victron’s response. I will continue to update here as I go.
 

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Not surprised, but did they state the technical reasons why you cannot connect a battery to the load side?
 

e9999

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COR, how did you mount the thing to your hood? Was that some special adhesive?
 
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Looks like Velcro underneath his panel. I’ll be using something called endurabond or eternabond or something like that. It’s for sealing up rv roof leaks and apparently extremely strong to withstand highway speed air flow.

Victron did not explain why any of that was unsafe, simply said to contact the local guys. Still waiting on their response. I think that there is no overcharge protection at least on the load side, so for a permanent install with zero draw most of the time that is obviously a big problem. I think the solution is to hook the mppt to the starter battery and then connect the batteries with the Cyrix battery link and leaving the load connection unused. I will hopefully know soon.
 
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Used a 3M product. Recommended from another forum.

3M Scotch 5952 VHB Tape
That’s a lot cheaper than what I was looking at. You’ve been happy with it? How long has it been mounted like that?

The local guy got back with me and my suspicion was correct, I just needed to add the battery combiner/isolator between start and aux batteries. The price he quoted me is double what amazon wants, but he likely prevented my car from burning down and if I have any trouble with the install it would be nice to have a real person to call so I’ll order from these guys. I’m waiting to hear back on a couple questions I just sent him to make sure I have a complete understanding. Basically the smart controller will be connected to the auxiliary battery, then that will run to the Cyrix combiner, which then runs to the start battery. The alternator connection is not changed at all so that will still charge the starting battery as normal. Once the auxiliary battery reaches float charge from the panel, the relay will open and charge the start battery to float. I’m waiting for confirmation that the smart controller will prevent overcharging both batteries and basically just safely shut down when both batteries are at float level. Also waiting to hear back if they either sell of recommend a specific battery start assist or any will do. Diagram attached. I welcome any comments or questions.

Note on the diagram: the only thing that would be different is the “multi/Quattro/charger” represents the smart solar charger and you will only use the “batt” connection. “Load” will not be used.

A3367448-B164-4BB1-B630-7B8CC8910EE9.png
 

e9999

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I don't think you have to worry about overcharging. Any good charge controller should give you full control over the charging scheme (voltages, times, types of battery etc). Maybe fully customizable. Just check the specs. Once you set the scheme properly, it should go back to float when fully charged. So no overcharging issues.
It's a bit odd that the starter battery would not be charged above float voltage by the solar system from what you describe, though. If it's not already fully charged by the alternator, it may take a long time for it to charge like that, and being limited to float voltage is not what's usually recommended for FLA charging, IIRC.
You may want to think about your priorities, basically. Starting and driving away, or cool :beer:? (I know what I'd pick... :D ) This ^ scheme seems to prioritize charging the aux battery over the starter one. Is that what you want? If not, you could connect the charger to the starter battery instead and then have some sort of combiner between the 2. Easy enough.
 
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Especially since I will have the start assist link to jump the start battery, yes I would like the solar power to be prioritized to the auxiliary battery. You’re exactly right on priorities. I also keep a portable jump pack that works really well, so a dead start battery is of just about the least concern possible. On top of app that, the alternator is still taking care of the start battery just like before.

As far as the charge controller preventing overcharge I’m 99% sure you’re right that I have nothing to worry about, I just have zero experience with one so I want to dot all my i’s and cross all my t’s with the pros.
 
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