Visit our Popular Forums

SilverHouseDreams · 10-25-2017, 10:56 AM

There is (small amount of) money to be made selling an in-line adapter for the 7-pin that includes diodes on the charge pin and a heatsink housing.

alano · 10-25-2017, 11:26 AM

If we can get a handful of folks who would be interested in an in-line diode solution, PM me. My son could put together a solution (under my guidance) at minimum wage. He's currently applying to colleges now as an EE.

larry9000 · 10-26-2017, 06:58 AM

Quote:

Originally Posted by uncle_bob

Hi

Well, first off, 12.2V is not a very encouraging battery voltage. On either the trailer or the TV with lead acid it should be up around 12.7 with the engine off and nothing going on.

The drop in the connector and wiring is proportional to the current flowing. With no current, there will be no drop. If you have (say) a one ohm resistance in the wire, you will get a 1 volt drop for every amp of current that flows. Obviously a real wire isn't going to be one ohm.

In the case that your TV does not switch off the 7 pin with the ignition off (some have a delay that is measured in hours), you will get a back feed to the TV battery. How much current depends on the wiring resistance.

If your Lithiums are sitting there putting out 14.5V and your alternator only gets up to 13.9, the Lithiums will try to run the TV through the 7 pin cable. To the degree they succeed at doing this, you will run down the Lithiums.

Lots of combinations and permutations ....

Bob

Measured the battery again this morning. 12.66 with nothing on. Drops to 12.26 when the ignition is turned on. Turned ignition off, and it rose, but only 12.5. Yes, that may be the leading indicator of the failing TV battery.

The 7 pin socket seems to disconnect quickly when ignition is turned off. But I think you identified the key issue- Lithiums in parallel with alternator when engine is running. I would think that they would eventually discharge to the 13.9v level, but there is one other issue- the 200w of solar panels on top. They will try to charge at 14.4 to 14.6v in sunlight.

Maybe I should reconsider the diode, or just unplug the appropriate fuse heading to the TT.

larry9000 · 10-26-2017, 07:48 AM

Quote:

Originally Posted by larry9000

Measured the battery again this morning. 12.66 with nothing on. Drops to 12.26 when the ignition is turned on. Turned ignition off, and it rose, but only 12.5. Yes, that may be the leading indicator of the failing TV battery.

Measured the voltage again a few minutes later. Back to 12.66v. Interesting behavior.

Back to the subject at hand: I am now thinking of putting a large inline fuse into the power connection coming from the 7 pin, but on the TT side. In normal operation I'll keep fuse out, essentially stopping any charging or even a connection. I'll keep the fuse handy if I get into a pinch where I'll need to charge the TT lithium from the TV. In theory, I won't need to do this.

larry9000 · 10-26-2017, 11:27 AM

Now, I'm back to thinking, as long as you have power to the TT that is disconnected when unkeyed, that everything is fine.

I had the Battleborn running the Bambi this morning, without any charging occurring. It was operating at 13.6 volts. Then I looked at the Battleborn spec sheet and it said, "Charging with an existing lead acid charger or inverter charger that bulk charges at 13.6 volts is acceptable, however it will take longer than a specialized li-ion charging system. Our batteries perform best at 14.4 volts bulk and absorption charge."

The way I read this is that the resting voltage is at 13.6, which is what I measured. Anything over that charges the battery, according to Battleborn. So my 13.9 alternator will not cause current to flow from TT to TV, since my alternator will be above that voltage.

SilverHouseDreams · 10-26-2017, 11:40 AM

Quote:

Originally Posted by larry9000

Now, I'm back to thinking, as long as you have power to the TT that is disconnected when unkeyed, that everything is fine.

I had the Battleborn running the Bambi this morning, without any charging occurring. It was operating at 13.6 volts. Then I looked at the Battleborn spec sheet and it said, "Charging with an existing lead acid charger or inverter charger that bulk charges at 13.6 volts is acceptable, however it will take longer than a specialized li-ion charging system. Our batteries perform best at 14.4 volts bulk and absorption charge."

The way I read this is that the resting voltage is at 13.6, which is what I measured. Anything over that charges the battery, according to Battleborn. So my 13.9 alternator will not cause current to flow from TT to TV, since my alternator will be above that voltage.

In the case that your TV does disconnect the charge line when the ignition is off, your are probably correct that their is minimal issue. If it levels out at 13.6V then you shouldn't be bleeding capacity from the TT to the TV, if the TT is at 100% SOC then nothing should happen...if it is below 100% SOC it will charge slowly.

If you unplug from shore power and the BattleBorn is at 14.4V, it will bleed some energy into the TV due to the voltage differential...but it would likely be minimal, I didn't have time to fully test this as I only noticed when preparing to take my TT to storage to avoid the city from towing it.

**wulfraat** · 10-26-2017, 01:04 PM

...... and help me understand again why you are not using a DC to DC converter to correctly address the issue of different voltages across the platforms (TV vs House batts)?

:-)

larry9000 · 11-10-2017, 07:17 AM

There's nothing like real world experience to see what works and what doesn't. After installing the BB lithium batteries I hitched to my TV (Toyota 4runner), and monitored what happened via the BMV 700 battery monitor.

With the TV turned off, no current flowed. This is because the Toyota has a relay that disconnects power through the 7-pin connector when the TV is off. Then I turned ignition ON, but without starting the engine. I had 7-8 Amps flowing from the TT to the TV. Yes, the lithium battery was trying to charge the TV battery. Then I started the motor. Suddenly I had 4 Amps flowing to the TT. All is good, right?

Wrong. As I drove, the charging current declined over the next 15 minutes, 4...3....2...1 Amps, and then finally went into reverse, with about an amp flowing to the TV from the TT. When I idled at an intersection, the discharge current was 2-3 Amps, but then would reduce to 1Amp or so when the engine revved again during driving. For some reason, the alternator doesn't put out the peak voltage/current as it did when the engine first started.

So, I ended up disconnecting the 10 gauge wire that comes from the TV to the +12V bus bar. This solved the discharging issue, and is the way I'm currently using the system on our 3 week road trip. I have solar panels that top off the batteries while driving, so it's not a problem.

But, yes, keeping the TV and TT batteries wired together when the two batteries have different voltage levels is problematic.

Troutboy · 11-10-2017, 07:24 AM

Good info, but still wonder why folks don’t use the Orion DC/DC converter that Wulfraat keeps discussing. It works beautifully and solves this issue. Isolating the TV and TT systems is a must for a proper install.

I guess disabling the connection is one way to isolate the systems....

DannyClark · 11-10-2017, 12:03 PM

Ok. As much as I like tinkering, I’ve got a long list of other priorities. Could one of you Gods if Airstream let me know which Victron 12/12 I need to get this done “correctly” please? I’ve got a 2017 F250 and 2017 26U with dual AC (50amp). Dual BB’s and no Solar (yet). I don’t mind spending the money (I’ll still be ahead vs. the Victron Batteries and necessary Battery Management) but I want it done right, and finally done lol. Thanks for any help.

**wulfraat** · 11-10-2017, 12:26 PM

Victron model number ORI121236100.

.... this is a 12-12- 30A converter. This is what AM Solar recommend.

You may call AM Solar to verify, and discuss how to wire it in correctly with common ground...

... or maybe Rich can chime in to confirm that this is the unit he ordered for his install (my install is only going to happen in the spring so I don't have my list of equipment pulled together yet)

Troutboy · 11-10-2017, 12:27 PM

I’m on the road but will pull up my info when I get home this weekend.

DannyClark · 11-10-2017, 01:20 PM

Excellent. Thanks Fellas. I’ve had a *#tch of a time installing my new BMV 712 yesterday and don’t want to hijack this thread, but I may start another when I have time to do it right. I’m still not sure ive got it right and I’ve read every thread on this subject (Victron BMV) available on the forum lol. I feel like I’m the only guy that can’t figure it out at this point lol. It’s relevant to this discussion I’m sure.

Troutboy · 11-10-2017, 02:53 PM

Danny, send me a PM and an email address and I’ll send you stuff on my setup to help. I have the BMV and Orion as well.

uncle_bob · 11-11-2017, 06:42 AM

Hi

The voltage regulator on your alternator is set up to charge the battery in your TV. It varies the voltage based on a charge curve and (possibly) temperature. It's going to drop back under 14V after running a bit.

Bob

SCOTTinNJ · 11-11-2017, 07:31 AM

Quote:

Originally Posted by larry9000

There's nothing like real world experience to see what works and what doesn't. After installing the BB lithium batteries I hitched to my TV (Toyota 4runner), and monitored what happened via the BMV 700 battery monitor.

With the TV turned off, no current flowed. This is because the Toyota has a relay that disconnects power through the 7-pin connector when the TV is off. Then I turned ignition ON, but without starting the engine. I had 7-8 Amps flowing from the TT to the TV. Yes, the lithium battery was trying to charge the TV battery. Then I started the motor. Suddenly I had 4 Amps flowing to the TT. All is good, right?

Wrong. As I drove, the charging current declined over the next 15 minutes, 4...3....2...1 Amps, and then finally went into reverse, with about an amp flowing to the TV from the TT. When I idled at an intersection, the discharge current was 2-3 Amps, but then would reduce to 1Amp or so when the engine revved again during driving. For some reason, the alternator doesn't put out the peak voltage/current as it did when the engine first started.

So, I ended up disconnecting the 10 gauge wire that comes from the TV to the +12V bus bar. This solved the discharging issue, and is the way I'm currently using the system on our 3 week road trip. I have solar panels that top off the batteries while driving, so it's not a problem.

But, yes, keeping the TV and TT batteries wired together when the two batteries have different voltage levels is problematic.

Thanks for testing. I'm now glad I never connected my TV charge wire.

Can you tell me what voltage your BB batteries sit at generally? Say at night with no large loads and fully charged? Thanks.

DannyClark · 11-11-2017, 10:55 AM

Thanks Trout (Being a new fly fisherman, im jealous of that avatar:-). When I’m back on a standard browser I’ll do so. On the mobile version I can’t find a PM link.

james.mileur · 11-11-2017, 11:07 AM

Quote:

Originally Posted by DannyClark

Thanks Trout (Being a new fly fisherman, im jealous of that avatar:-). When I’m back on a standard browser I’ll do so. On the mobile version I can’t find a PM link.

Just touch the poster's name at the top of the post and in the next screen, select message.

larry9000 · 11-12-2017, 08:13 AM

Quote:

Originally Posted by SCOTTinNJ

Thanks for testing. I'm now glad I never connected my TV charge wire.

Can you tell me what voltage your BB batteries sit at generally? Say at night with no large loads and fully charged? Thanks.

Sure. I'll let you know in a week. We've been traveling through Utah and Arizona, with electrical hookups at each stop so far. At the end of the coming week we will be boondocking for 3 days in Organ Pipe National Monument. Then I'll be able to see the behavior of the overall system. Will report back.

Troutboy · 11-13-2017, 11:31 AM

Quote:

Originally Posted by DannyClark

Thanks Trout (Being a new fly fisherman, im jealous of that avatar:-). When I’m back on a standard browser I’ll do so. On the mobile version I can’t find a PM link.

Sent you some pics and info, let m elbow if it helps or if you need more assistance.