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Old 03-17-2021, 01:04 PM   #1
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Dc-Dc only charging system

Thoughts on having just a dc-dc charger, an inverter/charger, and a lithium battery bank to run my Skoolie on full time. No solar. What would be the best way to do so?

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Old 03-17-2021, 02:14 PM   #2
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Well first you really need to outline your needs- what are you hoping to power with this setup?

Not knowing anything about your use case, I will say that no solar is going to hurt your prospects, a lot. Even a fairly big lithium bank will feel tiny when you don't have some sort of passive production to offset your costs.

Could you go into the rationale as to why you want to go with no solar? Batteries are the most expensive part of any system by far, and even a couple hundred dollars worth of solar up top will produce results similar to the much more expensive proposition of additional batteries.
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Old 03-17-2021, 04:45 PM   #3
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If you goal is to properly charge your house batteries while on the road (from alternator):
https://sterling-power.com/collectio...ers-up-to-400a
This is the one I have, happy with it.
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Old 03-18-2021, 01:42 AM   #4
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How many nights do you spend in powered sites, so you can charge mains power, compared to being off grid?

DCDC is only used while driving.

Do you drive a lot compared to time just sitting while off grid?

For the latter, if you have no solar, you need to run a gennie.

a 1000+W genset will power a 30-50A charger, so once you get your Ah per 24hr consumption numbers, you can figure out your gennie hours per day runtime required
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Old 03-18-2021, 08:45 AM   #5
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Quote:
Originally Posted by ABBus View Post
If you goal is to properly charge your house batteries while on the road (from alternator):
https://sterling-power.com/collectio...ers-up-to-400a
This is the one I have, happy with it.



the more I think about it i need one of these .. I have all AGM batteries and it seems they get a much better charge when ive charged them overnight with my Victron IP67 charger than when ive driven all day.. even days driving where im not using much electrical inside the bus.. I notice the victron charges with a higher voltage than my alternator typically outputs..
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Old 03-18-2021, 09:55 AM   #6
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I use a Sterling Power when I'm on the road and either shore power or an inverter genny to operate a Progressive dynamics converter to charge the house batteries. I wouldn't consider using a DC to DC alone.
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Old 03-18-2021, 11:00 AM   #7
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I use a Sterling Power when I'm on the road and either shore power or an inverter genny to operate a Progressive dynamics converter to charge the house batteries. I wouldn't consider using a DC to DC alone.
Jack
So this device isnít designed to charge my AGM batteries ?
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Old 03-18-2021, 11:09 AM   #8
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So this device isnít designed to charge my AGM batteries ?
The sterling should work well to charge AGM. I think Jack is saying he wouldn't rely on DC-DC charging alone. One would also want an AC-DC charger for charging when parked.

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Old 03-18-2021, 11:35 AM   #9
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The sterling should work well to charge AGM. I think Jack is saying he wouldn't rely on DC-DC charging alone. One would also want an AC-DC charger for charging when parked.

Ted

got it.. i have that piece.. im just concerned about how much of a charge I get when im driving.. as it seems when i do plug in, my Victron charger always charges at a decent rate meaning my batteries are taking a good amount of juice still ..
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Old 03-18-2021, 12:43 PM   #10
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SP can be had that charges up to 50 amps as long as your alt produces that much current. Jack
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Old 03-18-2021, 12:59 PM   #11
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Quote:
Originally Posted by cadillackid View Post
the more I think about it i need one of these .. I have all AGM batteries and it seems they get a much better charge when ive charged them overnight with my Victron IP67 charger than when ive driven all day.. even days driving where im not using much electrical inside the bus.. I notice the victron charges with a higher voltage than my alternator typically outputs..
FWIW, I use a Black and Decker AC to DC 15-amp charger. It charges my lead-acid starter battery doing time as a deep-cell up to just above 13.0VDC. That will drop overnight to about 12.4VDC.


Then I started using the charger as a power source with the battery as a capacitor, when using my newly installed sound system. It pulls 2-3 amps at low volume, up to 15 amps when playing reggae at high volumes (as shown on the charger's digital display). When I'm done using the charger for this (power supply), my battery is at 13.2VDC, and it only drops overnight to 12.7 or 12.8, where it should be when fully charged.


I wonder if your alternator has a bad diode. That was a problem with mine, but I had to take it apart to find it. It seemed to charge just fine, but the A/C system fans would not work, as they pulled power directly from the alternator (+) pole, before the battery isolator (diode type, not relay type). That led me to find the problem with the alternator that I didn't even knew existed until I dug deeper.....


Anyways, I'm looking forward to 4 AGM deep cycle batteries in the (hopefully) near future.


To clarify: the deep cycle batteries I see at WalMart do not say AGM on them, so I should not charge them with my alternator? That would be a reason to get the DC to DC charger, if it could save money in the short or long run. Those AGMs get pricey, and if the cost of 4 AGMs is more than the DC to DC charger and cheapo L.A. deep-cycles, why go that way?
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Old 03-18-2021, 03:41 PM   #12
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im using the Batteries Plus Blue tops which are supposed to be a true deep cycle AGM battery.. at home I charge them with a 25 amp Victron IP67 charger..



on the road they are just connected to my Bosch 1 wire alternator.. I dont have any reason to believe it has a bad diode.. I have good close to 14 volts even under pretty good load... I just have noticed the IP67 will be putting pretty decent amperage into my batteries even if i havent used them much. ie they were charged night before and i drove around alot during the day with minimal accessory usage.. or no parked usage to speak of.. my only reasoning as to why I think im not getting a great alternator charge on the batteries
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Old 03-18-2021, 03:56 PM   #13
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SP can be had that charges up to 50 amps as long as your alt produces that much current. Jack
Way more 50 amps. When the batteries are low enough, I see close to 200 amp.
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Old 03-18-2021, 04:15 PM   #14
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I have good close to 14 volts even under pretty good load...
So did I, until I replaced my blown battery isolator and then fixed my A/C system all in the same couple of months. Only then did I find the problem even existed. Circuits have always seemed simple to me. Charging stuff, and circuits that show voltage but no substantial amperage, has been more of a learning curve for me. Those circuits have tripped me up diagnosing problems with a digital multimeter. Voltage is fine, but a test light is very dim, almost no light at all. Only then I found the problems. That seems to be what was going on in my alternator/charging system. But then I know little about batteries, the different types, or the details in charging them.
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Old 03-18-2021, 04:31 PM   #15
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battery and voltage

I wonder what would be indicated voltage if a gage was wired at the batteries instead of anywhere else. Does not have to be permanent. I have seen more than once that resistance does not measure the same unloaded vs loaded in a circuit. I find cracked fuses that way... no load testing show continuity, but loaded up resistance goes way up at the crack in the fuse. poor connections at battery cables happen there too. to much lead oxide. I see mucho corrosion inside the terminal ends on battery cables that are crimped pretty often. lead terminals that are "melted" on to the ends of the cables, crimped connectors that are then soldered. Problem there is sometimes the cables break at the solder joint because of stress risers and vibration.

I am fan of bigger is better for wire gage sizes for charging, batteries, alternators, just to keep from losing that tenth of a volt here and there along the way. really seems to add up. Every single connection is another loss in the system. Anti corrosion paste meant for electrical connections for the high load stuff... like the grid heaters that pull 80 amps, starter motors, solenoid connections, inverter connections, always a pain in the ass to deal with and adds time to everything.

Ground loops, I have stayed away from using the bus body and the frame for ground paths. Every thing has a ground back to the batteries, including the alternator. I added grounds to all the clearance lights. The lights used the body for a ground path. I drilled and tapped the housings to add grounds. radiators, bus body, engine, cylinder head to engine block are tied together and grounded, there are these rubber strips that drag the ground so as to dump surface build up to ground when running down the road....

I have no idea if I have made a difference, but the way I see it, cant hurt either. except maybe in one case. High voltage power lines... a line on the bus could be insulated by the tires. By adding those body grounds that drag I may have added a problem there......

william
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Old 03-18-2021, 06:18 PM   #16
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The alternator is set up for starting batteries which charge at a lower voltage the deep cycle AGM. So either bringing them up all the way with a shore powered charger, or solar, or a dc to dc charger.


If you have enough charge to do what you want then maybe just let them be as charged direct from the alternator. With a top off every few days or so from shore power. Just a thought.
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Old 03-18-2021, 09:14 PM   #17
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thats how I do it now when I am parking the bus at home or in my storage unit I plug the batteries intoi the shore outlet..



of course when i travel away there is usually no ability to plug in at hotels or shopping centers.. sometimes my customer has a place to plug in when im on site.. but I usually dont ask unless they offer.. in chicago I knew I would need it with temperatures brutally cold and windy by the lake.. they just had me park in their heated garage instead.. problem solved..
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Old 03-24-2021, 04:25 PM   #18
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First thing is to control your power greeds. Most devices now don't use much juice. LED lighting. Laptops. Give up you coffee maker and microwave and I bet your problems will go away. For dc2dc I build a generator from a lawnmower engine and an alternator. I run the motor off propane. Whole thing cost me like $100. I haven't gotten into the solar thing yet. I will but I really don't expect much from it. Being in Canada and using the bus in the fall I think the angle of incidence and the cloud cover will be working against me. Beware of advice that solar is a big deal. Lots of rv enthusiasts hang out in the south west. Also beware of advice that you can pump 200A into your batteries. Not cool. Stay below 1/2 C.
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Old 03-25-2021, 12:12 AM   #19
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Going on one year using a Kisae Abso DC-DC Charger now charging LFP batteries (it also has AGM settings). So far so good running it at 30 amps (50 amp max). The built in solar charge controller has been working well also. I have a older weak alternator and a small 200 ah battery but 30 amps seems to work well. I havenít actually measured alternator temperature but am considering placing a cheap temperature sensor on it. In hot Summer conditions Iím considering turning it down to 20 amps. Maybe the higher solar output will make up the difference?.
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Old 03-25-2021, 07:39 AM   #20
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Sounds good. 30A is a good charge rate and it shouldn't be a big load for any alternator. If you can follow an 80/20 charge regime you should be in the clear for years to come.
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