Engine Charging - Tim's Way (without an extra alternator)

[Tim's RV]

Hi,
I was reading your article on charging batteries. I have thought about the problem with solenoids & isolators and I agree with your analysis. But I think there is a much easier and less expensive approach to the problem than adding a dedicated alternator and charging system for house batts.

I have wondered why nobody has come up with a DC to DC charger that would charge the house batteries from the engine battery system. When Heart Interface (now Xantrex) introduced the Echo Charger, I was excited and figured it was only a matter of time before they started producing one for charging house Batts off the engine charging system. But to my knowledge, they have not yet released such a device.
All they would need to do is slightly change the existing design to carry more current & regulate the voltage to what's optimum for house Batts. As far as discharging goes, echo charger already shuts off when input voltage drops below a pre-set point thus preventing discharge to the battery bank supplying the power. Someone should produce a "reverse echo", or better yet a "combo reversible echo". Wouldn't it be nice to have a DC to DC charger that would supply power from the charging bank to the discharged bank regardless of which is which? With todays technology it should be relatively simple to design and produce such a device. Let me know what you think.

Tim
www.TimsRV.net

[Sharkey]

Hi Tim;

An excellent observation! It's really not necessary to go though the job of mounting/wiring a second alternator if the one that's already there could be used in a more effective manner.

I've thought about isolators that can control the charge to two or more sets of batteries by controlling the alternator's field voltage and then splitting the output, but have run into the problem that there are so many possible combinations of vehicle charging systems, battery combinations, etc, so as to make designing a 'universal' controller almost impossible. A DC-to-DC would just look like another load to the vehicle's charging system, and it would simply increase current output to compensate. You'd have to set it up so that the vehicles's battery and accessories got priority over house battery charging.

My most recent isolator installation ran into such a problem. It was a 2000 Ford Power Stroke diesel. We purchased an isolator from Wrangler NW, one with a fourth terminal for ignition input. It kept blowing 10 amp fuses on the ignition input terminal. We were also having cold start problems. Turns out that year and model truck draws current for the glow plugs directly off of the alternator's B+ terminal. We ended up having to install a 100 amp contactor to supply the glow plug current via the ignition terminal.

Heart/Trace/Xantrex has always been a few ampere-hours short of a full charge, this is why they are suffering a brain-drain to Outback and now PV Powered. Why couldn't an Echo Charger be hooked up in reverse? You'd be limited to 15 amps is the drawback. ~There are ways~ of increasing current. How about an Echo Charger refit/upgrade kit? Purchase the off-the-shelf units, install a big heat sink full of MOSFETS, hook it up in reverse and let it fly?

I wonder if Vanner would consider researching such a device? The inverter part would be straightforward. With microprocessor controls, this could be a very sophisticated charger/isolator, with some form of display to show when the house batteries were completely charged, bulk charging, floating, etc.

Bi-directional? I suppose that it could be done. Are you thinking of allowing cranking battery charging from the house charging sources (generator, solar, AC-to-DC converter, etc?)

In any event, a solid-state isolator/charger would be a big improvement over what is available in the way of solenoids/diode isolators today.

Interesting things to think about.

[Tim's RV]

I have experienced similar problems with electronic isolators. As a matter of fact, I have run into so many problems with electronic isolators that I will no longer install them. On top of that I hate cutting into factory wire harnesses of brand new vehicles. Of course the solenoid type of isolators have their problems too. Besides the problems you mentioned in your article, reliability is a big issue with the solenoid type. For smaller battery banks, I have had pretty good luck with Standard's #SS584X. This is in their premium parts line-up and they use brass contacts. BTW if you know of a better continuous duty solenoid switch, at a reasonable price let me know.

As far as the DC to DC charger idea, I think it could be the solution to numerous problems.

You'd have to set it up so that the vehicle's battery and accessories got priority over house battery charging.

I don't think this would be a problem. The Echo charger already switches off when input voltage is below a pre-set point. All they would have to do is change this pre-set or make it adjustable so the installer could set it based on the needs of the particular system.

there are so many possible combinations of vehicle charging systems, battery combinations, etc, so as to make designing a 'universal' controller almost impossible.

I don't think there is a need to make a unit capable of controlling charge for every conceivable battery combination. But even if they made them completely 'universal', I would think that about 5-10 dip switches could cover 99% of the common configurations. But dip switches are only one of many possibilities. There could be many configurations pre-programmed into the unit and the user could use a touch pad to select what combination most closely resembles his systems needs. Currently Xantrex uses similar controls for their Link 10 & their inverter remotes. The user can select size of bank in AH, then select type of batteries (lead acid, or gel cell). I believe there are even settings for climate temperatures, ect.

Are you thinking of allowing cranking battery charging from the house charging sources (generator, solar, AC-to-DC converter, etc?)

Sure, I mean why not? After all this is the current function of the existing echo chargers. Many of my customers park for months at a time and end up with dead engine batts. I suspect there are other types of systems that would benefit from a bi-directional charger as well. Some marine applications come to mind & I'm sure there are others. I guess using 2 of the existing echo chargers (one wired in reverse) would be an option, but as you stated earlier, the charge rate would be limited to 15A and the presets for float voltage and on/off preset point may not be ideal for house batteries.

[Sharkey]

The solenoid we used in the Power Stroke installation was 100 amp, continuous duty. I seem to remember that it was cheap, less than $25.00:



There's seven pages of relays, including several others like this one here.