B2B charger (i.e CTEK) vs. ACR straight off the alternator

[Hopeless Diamond]

I'm looking to enhance the charging system for my house batteries in my pop-up camper, looking for some guidance from those much more knowledgeable than me (which almost everyone).

Camper - Hallmark K2 with 2 x 6 volt "golf cart" batteries, ~220ah. I have 200w of solar that does keep up, except for when there's clouds (seem to be few of them around all the time here in the PNW) and/or trees (see previous statement). The connection to the truck is via the 7 pin trailer connection, that is then extended back to the camper connection in the front of the bed, all on #10 wire. Not the most efficient circuit path.

The truck is a F350 diesel, single alternator, 157a output. Being a diesel it has the 2 batteries.

I'm planning on adding a larger charge circuit in order to help out getting the house batteries back up, typically while driving, but if needed, on a high idle stationary. I'm thinking of using at least #1, but may up to 1/0. Total circuit length is probably ~24' (to and from).

The CTEK and Smartpass can give me up to 80a of charging, although it doesn't really say what it draws to provide that (may not need to run the larger wires back). Seems to give a true 5 step charge and would provide isolation from the starting batteries. I guess on some long highway runs (that's one thing about the PNW, you can't get anywhere from here, you have to go somewhere else first, but then why leave in the first place.) it would be able to progress through the charging steps if needed.

The Blue Sea ML-ACR would provide the isolation, and would provide the house batteries as much as the alternator could give and they wanted to take. Would also have the added benefit of being able to combine to help starting if the staring batteries failed (original ones lasted 3-1/2 years, so you never know...). I don't think the charging output of the alternator on these things is very good for the longevity of the batteries, I watch the voltage, usually between 14.3 - 14.5, then some days it'll be 14.7 (built in desulfation?)

I'm trying not cranial intercourse this too much, but figure if I'm going to do it, do it right.

What do you guys think?

 

[DiploStrat]

Read (all of) This

Understand the problem: https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

Wire it up: https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf

Shortest answers:

-- If your alternator provides the correct voltages for your batteries (and yours does) then you don't need a B2B, use a relay based isolator.

-- If you have solar/shore power, and you want to share with your starter battery, use an intelligent relay, else, use a key controlled relay.

-- With lead acid batteries, big wires are essential to reduce voltage drop. Voltage drop has its greatest impact on charging speed as it is most significant at high amperages; as charging amperage drops, voltage rises. Use this to size your wires: http://www.calculator.net/voltage-d...nce=15&distanceunit=feet&amperes=100&x=38&y=6

-- Lead acid batteries are perverse in that as the surface charge builds, the voltage rises, and the charge rate drops. Thus it always takes much longer than you expect.

-- Because of these factors, it is hard to get a charging rate much over 150A and that drops rapidly. So, ironically, the CTEK D250S/SmartPass, which has a maximum charge rate of 80A, isn't actually that much worse than a relay based system. But why spend more money for less charge UNLESS you can save the cost of a separate solar controller.

Good luck!

 

[dwh]

The higher voltage is healthy for golf cart batteries, just keep an eye on the water levels.

If you don't need the MPPT solar charge controller of the 250s or the low-voltage disconnect of the Smartpass, then I don't see a big advantage of the Ctek setup over an ACR in your situation. Plus, as you noted, you probably need serious drive time to really see the benefit of the multi-stage charge profile.

And if you must have self-jump, then the ACR is probably better for that.

On this one, I'll vote for the ACR.

 

[dwh]

And no, higher voltage isn't desulfation, which is done with a high freq pulsing to induce vibrations in the plates.

 

[brianjwilson]

I won't pretend to be more knowledgable on the subject than the two who responded already. So I'll just post my experience with the ACR, and my thought about the ctek which I haven't used yet. Take it for what it's worth.

Some of the good and bad of the ACR. Obviously it is nice to be able to jump the main batteries if needed, assuming wiring is adequate. If not manually disconnected, solar will provide a charge to the truck batteries as well, which might be a pro or con. With my Tacoma and FWC I used the same batteries for starting and house batteries so they will all charged the same. If stationary for a couple days, the ACR connected all batteries when the solar was charging. After sundown, as the battery voltage drops the ACR disconnected. Pretty simple and effective.

Since my batteries were almost always topped off with solar, there was minimal voltage drop between starting and house batteries while running (minimal amperage = minimal voltage drop with 2 gauge wiring). So if your batteries are fully charged from shore power or solar and you hit the road, it isn't unreasonable to think that the house battery voltage will be equal (or close) to your starter batteries. If I remember right, my Toyota only charged at 14.1v or so, so I wasn't concerned. Having the manual control switch was handy of course, and if concerned I could simply disconnect the batteries. In fact I would often disconnect it during the summer when running around town, so the solar wouldn't overcharge the hot starter battery in the engine compartment after shutting down. Even if you're using temp compensation on your solar controller, your house batteries and starter batteries live in a much different environment. I think that is one of the main downfalls of using an ACR with separate solar controller.

Although I was very happy with the ACR, on my van I'm planning to use the ctek d250s and smart pass. I THINK. Basic plans include a single 225+ amp alternator, the ctek and smart pass charging an AGM 8d (225-255ah) and a couple hundred watts of solar. I believe the ctek charger needs to be within a few feet of the house battery according the to instructions, which would make sense to provide the correct voltage. In theory the wiring could be smaller as the voltage drop will be converted, but you'd want larger wiring for the bulk phase when the smart pass is being utilized anyway. I like that the solar controller is built in, and ideally it should just sit and monitor and control everything without any intervention. I like switches and controls but I also just want it to sit in the background and do its thing. Since it is one brain controlling solar and input from the alternator, I shouldn't need to worry about anything overcharging in theory.

How's that for cranial intercourse? Lol
I'm not 100% impressed with the ctek documents. Like I said part of me likes to have manual control, knowing how long things are charging at what rate and being able to adjust it. The ctek takes that away, which is a good and bad thing I suppose. I don't recall seeing anything about being able to adjust for battery type, it just says it works for everything (now I'll have to look again). I find it real easy to overthink things. :/

 

[brianjwilson]

I looked back at the ctek docs and apparently it does charge the starter battery via solar after the service batteries are topped off. Whether you consider that good or bad I don't know, just correcting my info I posted earlier. My thought is that it wouldn't send current to the starter battery until a full absorption charge has taken place, so it's probably less likely to over charge the hot starter batteries via solar.

 

[DiploStrat]

I looked back at the ctek docs and apparently it does charge the starter battery via solar after the service batteries are topped off. Whether you consider that good or bad I don't know, just correcting my info I posted earlier. My thought is that it wouldn't send current to the starter battery until a full absorption charge has taken place, so it's probably less likely to over charge the hot starter batteries via solar.

The great advantage of the CTEK is the integrated solar controller.

The starter battery is not going to overcharge. Lead acid battery charging is a lot less complicated than it seems. Grossly (and the experts will quibble a bit):

-- A lead acid battery will only take a charge when two conditions are met: 1. The charge voltage must be higher than the battery voltage. 2. There must be current available.

-- The charger can really only measure the voltage of the battery and the amp flow.

-- A charger can adjust its voltage and amperage.

So basically, a charger looks at the the connected battery(s) and provides voltage and current according to its profile and the response of the battery. As the voltage of the battery rises, the difference between the voltage of the battery and the voltage of the charger drops and the battery simply won't accept more current, even if the charger were not smart enough to measure this.

Remember also that lead acid batteries connected together seek to reach the same voltage at a rate determined by the resistance of the connection between the two batteries. So, connect a camper battery to your starter battery with 20 feet of AWG 10 wire and the alternator will never really "see" the camper battery. Current will flow, just not very fast. Make the connection with 10 feet of AWG 1/0 wire and the alternator will simply "see" one big battery.

Sooooooo, if your solar charger is connected to your camper battery and your camper battery is connected, in turn, to your starter battery, you can imagine that the camper battery will charge the starter battery UNTIL its voltage rises to the same level. The solar charger, in turn, is only looking at the voltage and amp flow. Once these reach the programmed levels, it shuts off or goes to absorb or float. Thus your ACR is not a problem as your solar controller is (hopefully) smart enough not to overcharge your camper battery, and that is all you need.

Sorry if this is long. None of this is hard to understand, but you do have to go step by step.

P.S. Your 2011 Ford is much more likely than your Toyota to have the higher voltages that your want with modern lead acid batteries. This would argue for an ACR unless the savings of the all in one aspect of the CTEK make it more attractive.

 

[Hopeless Diamond]

Thanks all, as I expected, smart thoughtful information. Lots of good info can be had here.

End of the day, it seems both approaches provide similar end results, and they achieve it with minor differences. I am thinking the ACR is a better solution for my situation. The camper does have a decent solar controller (Blue Sky Solar Boost 2000E) so this is just for a pure truck to camper charge connection. While the ACR could/would stay engaged and allow the solar to charge the starting batteries, I'm thinking any temperature differential downsides would be negligible. Assuming everything is in decent condition, the starting batteries would be in a fully (or almost) charged state when at camp. Most of the solar would be going to house loads and and or replenishing after a night of use. The starting batteries would be at or below the house battery temps and would probably just be taking a float charge if anything at all. Keeping the starting batteries topped of while sitting in one spot for a few days isn't a bad idea (assuming sunlight is getting through)

I've always like the idea of the CTEK, but it's probably a better solution if starting with a green field and being able to design around and utilize the entire system. For me, I have a decent solar controller in place, camper also has the Progressive Dynamics power center that has a 3 stage charger built in. Typically this only gets put into use to get a full charge into the batteries before a trip, (I don't leave it connected all the time, I just let the solar keep a float on the batteries when sitting).

Now to figure out an elegant way to get all this installed...

 

[DiploStrat]

Parthian shot: The Progressive Dynamics converter gets a terrible rap for one thing - it is alleged to go from bulk to float without a real absorb stage. Fine for folks whose campers spend most of their time plugged in, but less desirable for an overland camper. Not really an issue if you have any sunlight and your solar controller does have a proper absorb stage. A long, slow, high voltage absorb being the secret to a "fully" charged lead acid battery.

 

[Hopeless Diamond]

Yeah, somewhere down the road I may see if I can disable the built in charger and put in a good one. At this stage it's good enough for how it's used, and a case of run what ya brung. I'm working on my "if it ain't broke, fix it till it is", just haven't gotten to that yet

 

[dwh]

Yea, the PD is a two stage (bulk, float), with two different float voltages - low and (after some time) very low.

The marketing driods call that three stage.

Some have a "boost" button that just kicks the thing into bulk stage to push the battery up to the bulk stage voltage before dropping back to float. Then the marketing droids get a chubby and start singing about their awesome four stage charger.

But hey, without the IQ/4 brain, the Iota is a two stage as well.

The PD is a decent well built unit. Personally, with solar to provide an absorb stage, I wouldn't bother tinkering with the PD unless it failed.

As my dear old dad used to say, "drive it 'till the wheels fall off".