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Old 09-04-2016, 10:34 AM   #1
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DC-DC Chargers. Recommend a good one?

It's time to start building the electrics on my bus.

I'd like to be able to put some charge into the house batteries from the bus's alternator as I motor along. One of the few things I don't have on hand is a DC-DC charger.

What charger works for you? Could you recommend a good one?

Thanks
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Old 09-04-2016, 11:11 AM   #2
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im no electric expert but i'll give you my 2 cents.

to charge house batteries from your alternator, you should just need to run a hot wire from the truck battery to the house battery. on that wire, you'd install a battery isolator, to separate the 2 systems when your key is off. some isolators are electronic, some use a solenoid to seperate the systems.

i've heard, but don't know about possible issues with the size of your altenator. too small an alternator could burn up trying to charge too many batteries.

in my mind, when someone says a dc-dc charger, i think of one that changes voltage, like one that converts 12v to 24v
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Old 09-04-2016, 11:34 AM   #3
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Yeah, turf is right. You should really only need a battery isolator and a beefy length of welding wire connecting your house and chassis batteries if you're doing 12V house batteries. If you're doing 24v or 48v house batteries (which is an excellent, albeit complicated, idea) you then need a DC-DC converter. Those are pricier and harder to find. Sterling-power makes some of the best. Try them. Sterling Power Products
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Old 09-04-2016, 12:17 PM   #4
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I don't believe that you are correct. An automobile alternator is PERFECT for SLA (starting, lights, accessory which are sometimes called Cranking Batteries) batteries, but will not give a sufficient nor proper charge for deep cycle house batteries.

Folks might be doing it, but I don't think they are getting all the life they could be from their Deep Cycle Batteries because an alternator does not put out enough volts properly.

To help explain it, please read this: https://www.caravanworld.com.au/feat...gers-explained

BTW, I should have mentioned:

I have a 2000 GMC Savana van based schoolie. 6.5 Turbo Diesel with a stock 100 amp alternator.

I have 3 deep cycle 12VDC house batteries.

I'd like to install a DC-DC charger in my system. Could somebody recommend one?
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Old 09-04-2016, 01:01 PM   #5
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cool beans, i like the theory of a transformer charging off of the alternator.

i've been resigned to at best, leave home with the battery bank at 100% and and then only be able to recharge up to 80% while on the road, from a generator.

when i google dcdc chargers, i see converters. show some links.
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Old 09-04-2016, 02:01 PM   #6
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Quote:
Originally Posted by turf View Post

when i google dcdc chargers, i see converters. show some links.
I googled dc-dc battery charger 12vdc:

DC Input Battery Chargers for Lead Acid and SLA Batteries, for charging batteries from vehicles and other low voltage sources, 6 Volt, 12 Volt, 24 Volt, 36 Volt, 48 Volt, 12V

Somebody here must be using one of these or something like it.

It's Labour Day. I'll bump this thread when folks get back Tuesday.
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Old 09-04-2016, 04:23 PM   #7
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I have a 140 amp smart isolator (keyline 140amp dual battery isolator on amazon) from my start batteries to 2 auxiliary batteries. Cuts in at 13.3v and cuts out at 12.8 volts. My Aux system is small with a 12v bank of 225ah at 50%. The isolator coupled with 300 watts of solar work well together.
When I upgrade my battery bank I'll do away with the isolator to not overwork my allternator, and add more solar.

I consider my set up temporary and a great test run to figure out our needs power wise.
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Old 09-04-2016, 07:35 PM   #8
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What I would recommend is a charge controller. Sometimes called a solar
charge controller. These come in numerous sizes and types, the best being
MPPT controllers. The one I'm using has inputs from numerous sources like
solar panels, alternators, wind chargers etc. Basically this unit takes various
inputs and combines them and controls them to properly charge the type of
batteries you have on board. Should work good for your purpose and leave
room for expansion in the future.
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Old 09-06-2016, 02:34 PM   #9
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Originally Posted by Dragonpop View Post
What I would recommend is a charge controller. Sometimes called a solar charge controller. These come in numerous sizes and types, the best being
MPPT controllers. The one I'm using has inputs from numerous sources like
solar panels, alternators, wind chargers etc.
Brand name? Although I don't think I'll get involved in solar ... I learned a long time ago never to say never.

I did find this one. https://www.amazon.com/Flexcharge-NC.../dp/B000C168ZS

Comments indicate that "It can be used with Wind, solar, other DC alternators. It is a hackable / expandable controller.

This unit does not include a blocking diode (this prevents the power from the battery flowing back to your input source)."
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Old 09-06-2016, 06:32 PM   #10
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how does an alternator not charge house batteries well but does charge starting batteries? 14 volts is 14 volts regardless of what battery its going to.. my AGM batteries are 12.6 just like my starting batteries...

I have to think that driving the bus hours at a time is giving my batteries a good charge.. I would say that short trips wont charge an AGM deep cycle battery as much as a standard wet cell.. as the deep cyclers tend to require more time of "trickle charge" than the regular wet cell..

I venture to say a lot of us when we run our buses are running for long periods of time as opposed to a 20 minute trip here and there with dead house batteries between..

-Christopher
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Old 09-06-2016, 07:24 PM   #11
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I have been looking into that as well and the only thing I have come up with is the lead acid batteries are pigs that don't get fat.
The alternator doesn't quit turning out voltage and the lead batteries doesn't quit accepting it whether full or not? So in my mind combining another battery bank inline after the lead acid bank leaves the house bank in parallel with the starting bank without some geek piece (sorry) that can controll the alternator to shutoff the power to the start batteries as needed and charge the house batteries while on the road without starving the start/run batteries?
In my world of piping I would call these control valves for the start batteries to allow flow in when needed and turn it off when not and regulate the flow to the house when not needed for the starting/running batteries.
There might be switches and things out there that can do it but I say keep it simple? Of course a hard wired generator only works if the genny is running and shore power only works if you actually plug into it?
Wire your genny cord and shore cord into the same contacts and your switch's are non- existent cause you have to get out to plug into shore power regardless of any fancy switches?
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Old 09-06-2016, 07:49 PM   #12
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Originally Posted by cadillackid View Post
how does an alternator not charge house batteries well but does charge starting batteries?
-Christopher
Hey Chris.

The answer to your question lies in the differences between deep cycle and SLI (starting) batteries. They are very different in both purpose AND construction and require different methods of charging. If you want to get all the life out of your deep cycle AND get the most energy from them, they need to be charged properly.

Go back to post #4. Read the article I shared. Then, google your question and see for yourself. There is tons of material out there explaining the hows and whys.

Sorry, those are the geeky facts.

I can see I'm beginning to annoy folks. Sorry. Last post on this topic.
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Old 09-06-2016, 09:24 PM   #13
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I'll throw in a vote for a typical solar/wind/alternator charge controller. Since alternators put out ~14.7 volts you should be ok with a PWM controller. I haven't seen a charge controller that requires a blocking diode, by the way. They're smarter than that. My cheap Tracer MPPT charge controller is computer controlled and will take anything from 100 VDC to 14 VDC, convert it to the necessary charging voltage and will not allow energy to backflow. Easy peasy proper deep-cycle charging.

I also agree with not letting the alternator do the work on its own. Alternators are 'dumb' devices that can shorten the life of those all-too-expensive deep cycle batteries.
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Old 09-06-2016, 11:12 PM   #14
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I received a call back from my contact at Powerstream this afternoon. He tells me that based on my experience with their PST-PB1108 DC-DC converter/charger device, they're considering offering ruggedization as a value-add service on that product. Electrically it's really quite good; it just needs a little mechanical support if it'll be installed in a high-vibration environment. If anybody is interested in such a thing they should contact Powerstream.

Another product he recommended is PST-BC1212-15, which is a true multi-stage charger rather than a current-limited power supply as PST-PB1108 is.

Today I also called Midnite Solar to inquire about the charge controller idea. I've always had some doubt about it because PV applications are almost (or completely?) universally a step-down operation. They take a solar array with output of something like 17-600 volts and step it down to 14-ish for charging a battery bank. In contrast, this application could need to step up or down. Unfortunately Midnite had a very busy day today; a receptionist took a message from me but I didn't receive a call back yet. Maybe tomorrow.
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Old 09-07-2016, 08:26 AM   #15
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Starting to get a bit hacky, but I've had good luck coupling one of these 600w 10-60V to 12-80V step up converters connected to a treadmill motor (which is turned by a gas engine for use as a generator) then to my MPPT solar charger. The treadmill generator puts out ~60vdc when spinning. I especially wanted the 600w converter for the current limiting (which the step up converter also does), but the fact that it can step up voltage to 80vdc is useful to reduce loss through the transmission wires. As mentioned previously, the Tracer 4210rn MPPT charge controller can take up to 100vdc.

Using one of these units you could step up the alternators ~14.7vdc to ~16-20vdc or so and feed that into a PWM charge controller or, if your batteries are far from the alternator, you could increase the voltage to ~80vdc and feed it into an MPPT charge controller.
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Old 09-07-2016, 08:37 AM   #16
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Heehee.. I couldn't resist.. I just bought another one of those nifty little units to install between my bus's alternator and the MPPT charge controller. I don't drive the bus frequently and the solar has always provided enough charge.. I'm just curious now! I'll install a switch before the 600w power supply so it can be enabled or disabled.
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Old 09-09-2016, 03:59 PM   #17
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Just got off the phone with a support guy at Midnite. He explained that a PWM-style charge controller essentially connects input directly to output for a variable duration of time (thus "pulse width modulation"). The input has to be higher voltage than the output because there isn't any voltage boosting going on in there. The input also must be tolerant of having the load switched on and off. The PWM charge controller is designed to be supplied from something that inherently current-limits, so if instead it is connected to a power supply/alternator/battery that doesn't current-limit or at least doesn't as low as a solar cell would, then there's a risk of damaging the charge controller by running excessively high current pulses through it.

The MPPT is more complicated. It still doesn't have any voltage boosting going on; the input has to be higher voltage than the output. (We didn't talk about what the drop-out voltage is.) He explained that as the MPPT sweeps the amount of current it draws it expects the input voltage to drop as current rises. With a strong power supply (or battery, alternator) at the input that expected voltage drop won't happen in the way it would have with a PV input. A power supply might hit its current limit and just shut down. A battery or especially an alternator would try to supply the current without letting the voltage droop. He says it can be made to work, kind of, with the addition of series diodes and/or ballast resistors to make the input source behave a little more like a PV array would.

It made me laugh that he too suggested picking up an inexpensive inverter and mains-input battery charger..

So that's the story I got from Midnite: their charge controllers are not recommended for this use. Is there another charge controller vendor who does recommend their parts for this battery- (or alternator-) to-battery charging application?
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Old 09-09-2016, 10:40 PM   #18
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The PWM charge controller is designed to be supplied from something that inherently current-limits, so if instead it is connected to a power supply/alternator/battery that doesn't current-limit or at least doesn't as low as a solar cell would, then there's a risk of damaging the charge controller by running excessively high current pulses through it.
Yep! I needed a current limiter to connect my DC generator to my Tracer MPPT charge controller. Without one I could tell that I was burning out the generator. Things started to get real hot and sparky I set the limiter to put out around 30a@14.7vdc and it was doing well. I just need to set up a better system for tightening the v-belt that connects the engine to the generator...

I can't say I even gave it a second thought when putting DC generator power into the charge controller. It has instructions for wiring in a wind turbine, after all.
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Old 11-28-2019, 02:25 AM   #19
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I know I'm dredging up a 3 year old thread, but I came across it in researching the same question that OP is asking (roughly), and have some relevant knowledge to share in the hopes that others with similar questions will happen upon this thread as I have.


The two brands of DC to DC charge I have seen recommended for charging house batteries off the alternator are Sterling and Renogy. Renogy makes a 12v to 12v charger at either 20a or 40a, Sterling offers a number of different options in 12v/24v/36v and ranging from 20a to 100a.


It is my understanding that the purpose of these dc-dc chargers is to protect your house batteries and allow them to charge (1) efficiently (2) optimally (3) safely. Lithium batteries in particular and I think 'house batteries' in general need to be charged in particular ways based on depth of discharge, temperature, etc. Modern lithium batteries do best with a 3 stage charge (Bulk, Absorption, Float). Not charging them negatively effects the life of the battery.
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Old 11-28-2019, 09:35 AM   #20
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Originally Posted by dzl_ View Post
I know I'm dredging up a 3 year old thread, but I came across it in researching the same question that OP is asking (roughly), and have some relevant knowledge to share in the hopes that others with similar questions will happen upon this thread as I have.


The two brands of DC to DC charge I have seen recommended for charging house batteries off the alternator are Sterling and Renogy. Renogy makes a 12v to 12v charger at either 20a or 40a, Sterling offers a number of different options in 12v/24v/36v and ranging from 20a to 100a.
It is my understanding that the purpose of these dc-dc chargers is to protect your house batteries and allow them to charge (1) efficiently (2) optimally (3) safely. Lithium batteries in particular and I think 'house batteries' in general need to be charged in particular ways based on depth of discharge, temperature, etc. Modern lithium batteries do best with a 3 stage charge (Bulk, Absorption, Float). Not charging them negatively effects the life of the battery.
Iím also looking at the options for alternator charging including the Sterling and Renogy DC to DC Chargers. Thanks for bringing up this thread. Iíll correct what you mentioned about Lithium charging. Do NOT three stage Lithium batteries. Three stage is best for Lead Acid batteries.
Ive figured out a revolutionary and custom way to charge Lithium or Lead Acid batteries in a bus. Itís custom and requires rethinking the whole system. But it would transform the alternator charging from 30%-50% efficient to 70%-80% efficient and would integrate it with solar in a seamless system. So this is for top notch systems. Would be a investment. And it would be programmable. I hijacked the technology from cutting edge micro hydro/solar technology which is very efficient and integrated. You would even be able to see what itís doing using Bluetooth on your smart phone. Or on a computer 10,000 miles a way using WiFi.
This a system that expensive and probably only worth doing on a full size bus or Coach. And it requires a large solar array to clamp the alternator voltage.
Step 1: toss out the 12 volt alternator and bolt in a 48 volt alternator but do not connect it to the 12 volt starting battery. Or even better use a Harris alternator with powerful magnets and adjustable magnets.
Step 2: connect the 48 volt alternator to a programmable Mppt charge controller in parallel with a large solar array on the roof to the 48 volt house battery. The solar array acts like a zener diode and clamps the voltage of the alternator. The charge controller tracks the maximum power point. A very efficient and programmable setup.
Step 3: connect a big programmable DC to DC charger from the house battery to the starting battery. Now the starting batteries will also be connected to the solar and alternator through the house battery . Never need to worry about them being discharged.
Step 4: install a DC to DC converter from the house battery to the 12 volt DC loads. Or several step down DC to DC converters if the loads are big.
One could do a trick dual alternator setup if there is a massive 12 volt A/C load. But with a big DC to DC converter this extra alternator should not be necessary. But I would switch to a mini split inverter heat pump A/C that runs from the inverter/charger.
The Mppt charge controller can be programmed to charge Lithium or Lead Acid. The DC to DC Charger can be programmed to charge Lithium or Lead Acid. It offers flexibility.
Basically this is replacing the old low voltage analog DC systems in the coach with all cutting-edge technology high voltage DC digital systems. The entire system can be integrated together fairly easily. Well almost the entire system. Itís not the space shuttle.
This is the type of system Iím considering building on my Overlander Isuzu or my shortie skoolie.
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