Start Battery Powering lots of DC systems

Topic: Start Battery Powering lots of DC systems (Read 743 times) previous topic - next topic

Start Battery Powering lots of DC systems

August 19, 2025, 08:49:04 am

I am hoping that the FT wizards on this forum can help me with a confusing topic regarding my start batteries and how they are connected to the "house" system. I have disconnected the AGM house batteries completely as part of a lithium upgrade. However I am still getting DC voltage, from the start batteries, at the lug highlighted in the attached image. I thought I should not see any start voltage past the boost switch, unless it was turned on, but I am seeing that voltage when it is off.

This is on a 2002 U320, using wiring diagram dwg B-2126 (attached). I guess I would assume that the boost solenoid would isolate the voltage from the "house" side of the coach.

Appreciate any help

Re: Start Battery Powering lots of DC systems

Reply #1 – August 19, 2025, 10:09:31 am

Do you have a Tricklestart or amprestart? or any other house charging to start batteries?

Re: Start Battery Powering lots of DC systems

Reply #2 – August 19, 2025, 10:40:14 am

Quote from: craneman – August 19, 2025, 10:09:31 am

Do you have a Tricklestart or amprestart? or any other house charging to start batteries?

Or solar panels/maintainer on the roof?

Re: Start Battery Powering lots of DC systems

Reply #3 – August 19, 2025, 11:51:57 am

Unless I am misreading your problem and can't bow up your print verry well you may have a bad/shorted out boost relay. If you unhook one of the cables on that relay and the voltage goes away then that could be your problem.

Mike

Re: Start Battery Powering lots of DC systems

Reply #4 – August 19, 2025, 12:46:39 pm

Quote from: craneman – August 19, 2025, 10:09:31 am

Do you have a Tricklestart or amprestart? or any other house charging to start batteries?

There is know other charger that I am aware of, haven't found anything from PO and as far as I know FT didn't iinstall anything else.

Re: Start Battery Powering lots of DC systems

Reply #5 – August 19, 2025, 12:47:10 pm

Quote from: Michelle – August 19, 2025, 10:40:14 am

Or solar panels/maintainer on the roof?

No Solar anyplace...yet

Re: Start Battery Powering lots of DC systems

Reply #6 – August 19, 2025, 12:49:44 pm

Quote from: Pamela & Mike – August 19, 2025, 11:51:57 am

Unless I am misreading your problem and can't bow up your print verry well you may have a bad/shorted out boost relay. If you unhook one of the cables on that relay and the voltage goes away then that could be your problem.

Mike

I will try that, when I test it it appears to be functioning, e.g. turning the boost switch on I here it click and I can see the batteries combine (well I did when I had the house batteries connected). It does seem to be allowing the start battery current to backflow through the boost switch, thats what I am hoping to confirm.

Thanks!!!!

Re: Start Battery Powering lots of DC systems

Reply #7 – August 19, 2025, 01:21:38 pm

If your coach has a diode based battery isolator, it is possible that the battery cables from the battery banks are not correctly attached at the isolator, OR the isolator diodes might have failed allowing current to flow between the two battery banks.

The first scenario is more likely than the second...but never underestimate the ability of the electric system to offer up interesting puzzles.

Re: Start Battery Powering lots of DC systems

Reply #8 – August 19, 2025, 01:38:29 pm

Quote from: RKs02U320 – August 19, 2025, 12:46:39 pm

There is know other charger that I am aware of, haven't found anything from PO and as far as I know FT didn't iinstall anything else.

If there were a Trik-l-Start or Amp-L-Start, it would most likely be mounted on the isolator and look like this (the isolator is mounted inside the engine compartment at the foot of the bed)

ETA - my memory was jogged that for some years, FOT was offering a voltage sensing relay, and many forum members have also installed a Blue Sea Automatic Charging Relay

Charging both House and Start Batteries

Photos of several devices can be found in links in that thread, although I didn't see any showing what make/model FOT might have been selling/installing.

Re: Start Battery Powering lots of DC systems

Reply #9 – August 19, 2025, 03:38:34 pm

I would start by disconnecting the B5 000 cable from the chassis batteries to the boost solenoid. Does the rest of the 12V power disappear? Maybe a boost solenoid that isn't disconnecting completely?

Re: Start Battery Powering lots of DC systems

Reply #10 – August 19, 2025, 05:10:42 pm

Quote from: Michelle – August 19, 2025, 01:38:29 pm

ETA - my memory was jogged that for some years, FOT was offering a voltage sensing relay...
...I didn't see any showing what make/model FOT might have been selling/installing.

I remember reading past posts wherein a "factory installed" BEP Voltage Sensing Relay was discussed.

Re: Start Battery Powering lots of DC systems

Reply #11 – August 19, 2025, 05:13:26 pm

Quote from: Chuck & Jeannie – August 19, 2025, 05:10:42 pm

I remember reading past posts wherein a "factory installed" BEP Voltage Sensing Relay was discussed.

And here's one of your posts showing a wider view of one installed - also in the area of the isolator

new Batteries

Re: Start Battery Powering lots of DC systems

Reply #12 – August 19, 2025, 05:31:53 pm

Quote from: Michelle – August 19, 2025, 01:38:29 pm

If there were a Trik-l-Start or Amp-L-Start, it would most likely be mounted on the isolator and look like this (the isolator is mounted inside the engine compartment at the foot of the bed)

[attach type=thumb]143036[/attach]

ETA - my memory was jogged that for some years, FOT was offering a voltage sensing relay, and many forum members have also installed a Blue Sea Automatic Charging Relay

Charging both House and Start Batteries

Photos of several devices can be found in links in that thread, although I didn't see any showing what make/model FOT might have been selling/installing.

Interesting topic, I don't seem to have one of these trickle starts attached to my battery isolater perhaps it's something that was fitted on newer model ft, I have the same isolator as the picture you posted but without this trickle start, what does this trickle start do please, mine is a 1990 villa,

Re: Start Battery Powering lots of DC systems

Reply #13 – August 19, 2025, 05:58:03 pm

Quote from: kevo0000 – August 19, 2025, 05:31:53 pm

Interesting topic, I don't seem to have one of these trickle starts attached to my battery isolater perhaps it's something that was fitted on newer model ft, I have the same isolator as the picture you posted but without this trickle start, what does this trickle start do please, mine is a 1990 villa,

They weren't OEM, but added by owners later (ditto the other options).

Basically, if the house batteries are at a higher voltage than the chassis batteries, they allow current to flow into the chassis batteries to charge them. It maintains the chassis batteries if the coach is plugged in while stored.

Trik-L-Start is out of business (the owner of LSL products passed away a couple of years ago), although another company, House2Start, has started producing a similar product: Charging chassis battery

Re: Start Battery Powering lots of DC systems

Reply #14 – August 19, 2025, 09:19:00 pm

It is needed because the start batteries are only charged by the engine and not by the coach power.

Re: Start Battery Powering lots of DC systems

Reply #15 – August 20, 2025, 05:15:37 am

Quote from: kevo0000 – August 19, 2025, 05:31:53 pm

Interesting topic, I don't seem to have one of these trickle starts attached to my battery isolater perhaps it's something that was fitted on newer model ft, I have the same isolator as the picture you posted but without this trickle start, what does this trickle start do please, mine is a 1990 villa,

Yes I understand that now wasn't sure if I had something missing that should be there, as I've been parked in the same place for quite a few years now, my solar is enough to keep my house batteries topped up and once a week I swap over to the vehicle batteries for a day and keep the starting batteries topped up, any topic thats to do with charging batteries and solar and power inverters etc I'm always well interested, from end of September to beginning of march I don't really get many amps going in to the batteries, sun is just not high enough, so I just make do with a small 700watt generator that I bought from temu and I use a nokko genius 10 amp charger plugged into that and just keep both sets of batteries charged through the winter months, I use trojan 6 volt batteries lead acid wired in series t105 batteries 225 amp capacity, I have 2 banks of those which gives me 450 amps total. I know alot of people seems to be going down the lithium battery route now, but I've heard so many stories of fires caused by lithium batteries that I'm a bit paranoid about it so I stick with lead acid

Re: Start Battery Powering lots of DC systems

Reply #16 – August 20, 2025, 09:26:18 am

Without any load a sensitive meter will read voltage on back side of a large power diode. Use a test light and see if it can actually draw current.

Re: Start Battery Powering lots of DC systems

Reply #17 – August 20, 2025, 05:25:45 pm

Quote from: Chuck & Jeannie – August 19, 2025, 05:10:42 pm

I remember reading past posts wherein a "factory installed" BEP Voltage Sensing Relay was discussed.

FT installed one for me a few years ago. Worked great. I just removed it as I switched coach batteries from AGM to Lithium.

Re: Start Battery Powering lots of DC systems

Reply #18 – August 20, 2025, 06:30:46 pm

Quote from: kevo0000 – August 20, 2025, 05:15:37 am

I know alot of people seems to be going down the lithium battery route now, but I've heard so many stories of fires caused by lithium batteries that I'm a bit paranoid about it so I stick with lead acid

The fires you refer to are caused by lithium-ion batteries, such as those used with e-bikes and many small electronic devices. The LiFePO4 batteries commonly used in RVs are not susceptible to fires. They are chemically stable and nearly incombustible. There is little chance of them combusting even if punctured or short circuited. You shouldn't let fear of a fire keep you from switching to lithium.

Re: Start Battery Powering lots of DC systems

Reply #19 – August 21, 2025, 07:34:18 pm

Quote from: dbennett9 – August 20, 2025, 06:30:46 pm

The fires you refer to are caused by lithium-ion batteries, such as those used with e-bikes and many small electronic devices. The LiFePO4 batteries commonly used in RVs are not susceptible to fires. They are chemically stable and nearly incombustible. There is little chance of them combusting even if punctured or short circuited. You shouldn't let fear of a fire keep you from switching to lithium.

Yeah thank alot for that info, funny you say about ebike, cause I got one they are so mutch fun but they warn you in the instructions never to leave the bike with the battery in direct sunlight and I would never leave the battery charging, all the electric car batteries must be lithium ion, there have been so many electric vehicle fires in the uk

Re: Start Battery Powering lots of DC systems

Reply #20 – August 23, 2025, 09:53:01 am

Quote from: kevo0000 – August 21, 2025, 07:34:18 pm

all the electric car batteries must be lithium ion, there have been so many electric vehicle fires in the uk

Yes, my understanding is that electric cars use lithium-ion batteries and are susceptible to fires. I believe the LiFePO4 batteries are too expensive for car manufacturers. I wouldn't have lithium batteries in my coach if they were lithium-ion batteries. I also have an e-bike, and I am very careful not to leave it charging unattended. I also try to charge it outside in the shade. I have looked into a fireproof storage box, but the cost and size have kept me from purchasing.

Re: Start Battery Powering lots of DC systems

Reply #21 – August 23, 2025, 05:07:45 pm

Rich Bowman told me that the engine batteries do not charge from the shore power, I got a Tric-L- Charge which did work but never brought the voltage up adequately, its wiring was a very light gauge, At the Branson Grandvention I had a different model installed that has heavier wiring, looks similar to Chuck & Jeannie's shown in a previous reply,
I cannot find the paperwork for it and there is no name on the unit but i believe it came from Foretravel. Cost a few hundred bucks and we have had no battery issues since,
Got rid of the glass pack starter batteries and have old fashioned lead cell batteries that do a great job even in the coldest Ohio weather.

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