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| Smart Battery Isolator/combiner [message #328312] |
Tue, 16 January 2018 15:53  |
Tomtom
Messages: 20
Registered: June 2017
Location: Huntington Beach, CA
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I've read a bit on this forum and other places about these, but thought I'd summarize what I've done and learned and see if anyone had any thoughts to add.
I've seen these things called smart/automatic isolators, combiners, relays, etc, but basically they are a relay with some brains built in. You connect the relay between your house and chassis batteries and it senses when you are charging and closes the relay to charge both battery systems. When you are not charging, it senses this and opens the relay. Well, that's what I expected anyway, and it does do this, but with a catch that I will get to.
I added a solar panel to the coach 6 months ago or so, and I thought a relay like this would be really neat since the solar panel would keep both the house and chassis batteries charged while in storage. It would also charge both with the engine running or when connected to shore power. Also, a fringe benefit was not having the voltage drop of the stock diode battery isolator when charging from the engine alternator.
This is the one I bought
http://www.littelfuse.com/products/battery-management/battery-isolators/smart-battery-isolators/48525.aspx
I bought the 85 amp flavor and decided to install it in place of the diode style isolator and keep the stock boost relays as is. I also installed a indicator on the dash and a momentary switch for this relay (independent of the stock boost switch). I can't think of any use for the momentary remote switch, but I had a spot for it and put it in anyways. I've had it installed for a few weeks and so far works great and as advertised. When the voltage of either side is above 13.2 volts, it senses charging and closes the relay. But, when the charging is finished, (i.e. the sun goes down and/or the engine is turned off) it still stays closed! This is because it's setpoint for not charging is 12.7 volts. Turns out when fully charged the voltages are a little higher than 12.7 volts, and since there is essentially no draw on the battery in storage (except ironically the draw of this relays coil), it stays closed. Eventually, a few hours later the voltage goes below 12.7 and the relay will open. So, in my storage scenario, this will be a daily occurrence. Solar will top off the batteries, sun goes down, smart isolator relay drains batteries a bit, relay opens, repeat tomorrow. I can't find a published current draw for the relay, but my guess is that it is about an amp. On a 75deg or so day, the relay is hot to the touch, so probably about 130 F. If it wasn't for the high temps, I might have not given any of this a second thought. Even as a potential fire hazard, I'm not too concerned. It wasn't until a thought about some critter looking for a warm spot to hang out and maybe munch on some wires while he's there that I got to thinking that maybe this isn't a good idea.
I did notice some other similar products. A friend of mine uses this one on his SOB
https://www.bluesea.com/products/7601/m-Series__Automatic_Charging_Relay_-_12_24V_DC_65A
It only draws 90 mA when closed so likely doesn't get hot. It's only rated at 65 amps though, but when you consider the 60 amp breaker to the house batteries, it would probably work. I didn't mention this above, but the alternator is connected directly to the chassis battery in this installation, and my solar only can make about 5 amps.
Here is another bluesea type. This one has a momentary coil for moving the relay either direction so it doesn't have a continuous electrical load in either state. Seems like the best solution to me. Costs a bunch though.
https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A
What do you guys think?
Thanks,
Tom C
77 Kingsley
Huntington Beach, CA
Tom
77 Kingsley. Mostly Stock, 455, Quad bag, tachometer, 16"wheels, Macerator.
Southern California, huntington beach
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