Advice on Solving Voltage Drop to Starter

Topic: Advice on Solving Voltage Drop to Starter (Read 1262 times) previous topic - next topic

Advice on Solving Voltage Drop to Starter

February 15, 2022, 12:18:15 am

I noticed intermittent sluggish starting recently that the boost would overcome. I read many of the previous posts and isolated the problem. My NEG (-) path is fine with every point measuring below .5V drop, and less than a .5V drop from the NEG (-) battery terminal to the starter motor ground post. The POS (+) battery post to the POS (+) chassis single terminal bus junction also measures less than .5V. From that stacked POS(+) terminal bus to the starter POS(+) lug, however, drops 2.5V. There appears to be several ways to solve my problem. I should add that the cable ends at the starter are pristine.

1. Remove, clean, tighten and grease all the wires on the POS(+) chassis terminal bus. Recheck and call it a day.
2. Do #1 and replace the existing cable to the starter with a 4/0 cable, or double up on the 3/0 cable from the POS(+) terminal bus to the starter.
3. Do #1 and add a new 4/0 cable directly from the battery to the starter laying it over the existing 3/0 cable from the POS(+) terminal bus. Leave the cleaned POS(+) terminal bus wires as factory.
4. Replace the single POS(+) bus with a 3 or 4 terminal bus and reuse all the existing cables.
5. Some combination thereof or something different.

Heat precautions have and will be taken. I don't want to make unnecessary work and expense, but I will happily pay not to revisit this ever again! Over the years I melted wires and replaced the starter. Took heat precautions. Attacked the ground bus successfully, but I overlooked the presence of a POS(+) bus. Dumb. All of these solutions will reduce the voltage drop, but I'm wondering if there is a "best" and easiest solution. I can't try all of these avenues, but this forum has experience with all of them. Please let me know your results or regrets, how to best avoid a jam or any preference you have in retrospect. I'll be attacking this last leg in a couple of days. Thank you for all your collective wisdom and experience. What a resource to talk to folks in the know.

Re: Advice on Solving Voltage Drop to Starter

Reply #1 – February 15, 2022, 07:15:37 am

I am not sure how you are getting a .5V drop? Are you going between positive and ground at different locations and seeing a difference? If there is no load there should not even be a .5V drop unless not good connections. What am I not understanding?

Re: Advice on Solving Voltage Drop to Starter

Reply #2 – February 15, 2022, 09:20:00 am

Add a new ground cable.

Re: Advice on Solving Voltage Drop to Starter

Reply #3 – February 15, 2022, 11:20:46 am

Sorry for the confusion. I am measuring voltage drop under a 500amp load. I measure DC volts from NEG battery post to NEG starter post and every point in between. Separately I also measure DC volts from POS battery post to POS starter post and every point in between. I am measuring the voltage loss within the circuit...cable loss, connection loss, etc.

I already added additional grounds and the .5V drop is within spec for a Delco Remy starter. Probably due to all the connections and 3/0 cable loss. What is bad is that 2.5V drop from the common POS terminal to the POS starter post. That is what I'm trying to improve. Getting only 10V to the starter is bad news. Just trying to figure out the easiest and most effective way to go given the choices. Thanks.

Re: Advice on Solving Voltage Drop to Starter

Reply #4 – February 15, 2022, 11:25:54 am

How about using a large jumper cable in addition to your OEM battery to starter cable and then checking voltage? This way, you could see if there is an increase in voltage.

How about the starter itself? Starter drag or internal problem?

Pierce

Re: Advice on Solving Voltage Drop to Starter

Reply #5 – February 15, 2022, 11:39:48 am

Good idea. Thank you, Pierce. I will do that before digging into rat's nest POS bus. The starter is relatively new and works fine. Assuming the jump confirms my findings would you favor just adding a 4/0 cable from the battery directly to the starter, clean up the common POS terminal bus and leaving it in place? I'm just hesitant in adding and taking away stuff from the original design. No way I can out engineer the engineers. All I want is to get on the road and stay on the road.

Re: Advice on Solving Voltage Drop to Starter

Reply #6 – February 15, 2022, 01:18:57 pm

Quote from: Hach – February 15, 2022, 11:20:46 am

What is bad is that 2.5V drop from the common POS terminal to the POS starter post. That is what I'm trying to improve. Getting only 10V to the starter is bad news. Just trying to figure out the easiest and most effective way to go given the choices. Thanks.

2.5 volts at 500A is 1,125 watts so all you need to to is run you hand over the cable and connections and wherever your hand gets stuck, there you are!

Re: Advice on Solving Voltage Drop to Starter

Reply #7 – February 15, 2022, 01:31:12 pm

Quote from: Hach – February 15, 2022, 11:39:48 am

Good idea. Thank you, Pierce. I will do that before digging into rat's nest POS bus. The starter is relatively new and works fine. Assuming the jump confirms my findings would you favor just adding a 4/0 cable from the battery directly to the starter, clean up the common POS terminal bus and leaving it in place? I'm just hesitant in adding and taking away stuff from the original design. No way I can out engineer the engineers. All I want is to get on the road and stay on the road.

Yes, add an additional cable. But the original designers left a lot to be desired in quite a few areas! If using welding cable, make sure it's supported if there is a longer unsupported area as welding cable is great with lots of fine copper wires but since it has to move around with the guy welding, it has to be flexible. Tie-wraps (good quality) do an excellent job. I also added an approx 2 foot extra ground cable to the closest frame spot to the batteries.

Pierce

Pierce

Re: Advice on Solving Voltage Drop to Starter

Reply #8 – February 15, 2022, 02:04:38 pm

Quote from: Hach – February 15, 2022, 11:20:46 am

Sorry for the confusion. I am measuring voltage drop under a 500amp load. Separately I also measure DC volts from POS battery post to POS starter post. What is bad is that 2.5V drop from the common POS terminal to the POS starter post.

So by doing this you have isolated your fault. Go to the hot buss and measure both voltage across the input post and the output post. I suspect your resistance and drop is there. Don't be surprised that when you remove the nut the post fails do to internal corrosion. If its not there great start checking voltage across end to end of each cable. Could have one failing. Check each connection "lug to post" in and out for voltage. Having a 500 amp load cell makes it so much easier to duplicate fault
Scott

Re: Advice on Solving Voltage Drop to Starter

Reply #9 – February 15, 2022, 04:44:21 pm

Thank you, Scott. Good guidance. I will drill down on that POS bus and measure the cable out to starter carefully. The battery cable to the bus checked out fine. If it's the terminal bus, then I'll tear it apart and replace it. If it's the cable out to the starter, then I'll replace that or just double it up. Once I see how that works out, then I'll decide whether or not to run an independent 4/0 cable from the battery POS post directly to the starter POS post. Good plan, I think. Thanks again. I wasn't sure if I should attack the bus directly or bypass it with a new battery to starter cable. Your approach lets me decide based on findings rather than guessing. Yes, the carbon pile load tester is a blessing.

Re: Advice on Solving Voltage Drop to Starter

Reply #10 – February 15, 2022, 04:56:07 pm

A 4/0 cable to the starter is probably more than is needed. I had similar slow starter issues. The two common posts (plus and minus) on my coach could be neither tightened or loosened. With some effort to do so they both failed.

And they have too many lugs per post using current standards. Replace them with a three post bus bar, clean every lug til it is shiny, reassemble using a terminal grease, not dielectric grease. Performance will improve dramatically.

BEP Marinco Pro Installer 650 Amp, 3-Stud Heavy Duty Bus Bar

There are probably a lower amp capacity ones that would work, maybe cheaper. Batteries go to the center post and then to the starter. All other connections on the side posts.

NO-OX-ID "A Special" Conductive Terminal Grease

See Start Battery Wiring Modification

Re: Advice on Solving Voltage Drop to Starter

Reply #11 – February 15, 2022, 05:06:52 pm

Quote from: Hach – February 15, 2022, 04:44:21 pm

Yes, the carbon pile load tester is a blessing.

Agree, one of these can test batteries, test cables as you have done, and put various loads on the alternator to test the output.

I keep a saved search on eBay, there is an "open box" AutoMeter SB-5 800-Amp tester listed with free shipping that would be a good buy for someone.

I have one that I bought on eBay a few years ago non-working with smashed meters and I refurbished it with new meters from AutoMeter.

Re: Advice on Solving Voltage Drop to Starter

Reply #12 – February 15, 2022, 05:08:02 pm

Quote from: Hach – February 15, 2022, 04:44:21 pm

Thank you, Scott. Good guidance. I will drill down on that POS bus and measure the cable out to starter carefully. The battery cable to the bus checked out fine. If it's the terminal bus, then I'll tear it apart and replace it. If it's the cable out to the starter, then I'll replace that or just double it up. Once I see how that works out, then I'll decide whether or not to run an independent 4/0 cable from the battery POS post directly to the starter POS post. Good plan, I think. Thanks again. I wasn't sure if I should attack the bus directly or bypass it with a new battery to starter cable. Your approach lets me decide based on findings rather than guessing. Yes, the carbon pile load tester is a blessing.

Roger is spot on in regard to those bus posts. They live in the wheel well and collect crap. So IMO i like to be able to disconnect the Negative post easily in case of a emergency or accident. He actually installed on/off switches which is very convenient, but just keeping a dedicated wrench near is fast enough for me.👍👍

Re: Advice on Solving Voltage Drop to Starter

Reply #13 – February 15, 2022, 05:23:21 pm

Quote from: prfleming – February 15, 2022, 05:06:52 pm

Agree, one of these can test batteries, test cables as you have done, and put various loads on the alternator to test the output.

I keep a saved search on eBay, there is an "open box" AutoMeter SB-5 800-Amp tester listed with free shipping that would be a good buy for someone.

I have one that I bought on eBay a few years ago non-working with smashed meters and I refurbished it with new meters from AutoMeter.

Yes I 100% agree. Analog volt meter, Carbon pile load cell, and the Fluke. Bunch of test lights with alligator clips on the ends to put across connections for fast location indication.

Re: Advice on Solving Voltage Drop to Starter

Reply #14 – February 15, 2022, 05:50:59 pm

Quote from: Hach – February 15, 2022, 04:44:21 pm

Thank you, Scott. Good guidance. I will drill down on that POS bus and measure the cable out to starter carefully. Yes, the carbon pile load tester is a blessing.

I know this sounds insulting, but what I used to do for a living, misunderstanding got people hurt.

If that's an adjustable carbon pile you can dial it back to whatever, 10A would be nice, and check the individual junctions at the bus(ses) for developed voltage.

Re: Advice on Solving Voltage Drop to Starter

Reply #15 – February 15, 2022, 08:58:52 pm

I noticed you replaced the starter in the past. Lots of time, the problem has a lot to do to the repair/replacement. Before you do anything, I would check the connections at the end of the big cable and the terminal it connects to. They both should be nice and shinny with no trace of corrosion. Shoot the connection with a IR gun after cranking.

Pierce

Re: Advice on Solving Voltage Drop to Starter

Reply #16 – February 15, 2022, 11:19:33 pm

Thank you all for your help.

Re: Advice on Solving Voltage Drop to Starter

Reply #17 – February 16, 2022, 12:36:13 am

Quote from: Old Toolmaker – February 15, 2022, 05:50:59 pm

I know this sounds insulting, but what I used to do for a living, misunderstanding got people hurt.

If that's an adjustable carbon pile you can dial it back to whatever, 10A would be nice, and check the individual junctions at the bus(ses) for developed voltage.

Mine drops off at about 50 amp load. 50 amp load on starter cable is quite manageable I generally use for batteries and alternator output/voltage, rpm. At full load I never operate very long and suspect duty cycle wouldn't be more than 3% still great T/S tool IMO

Re: Advice on Solving Voltage Drop to Starter

Reply #18 – February 17, 2022, 12:14:05 pm

When I cleaned up those big single point buses they didn't take kindly to removal of the wires and cleaning. Had to replace both the positive and negative after they broke while removing the nuts.

Re: Advice on Solving Voltage Drop to Starter

Reply #19 – February 18, 2022, 12:45:42 am

Thank you all. I'm armed and ready with my Marinco 3 terminal 600Amp bus (Bay Marine Supply) based on the Forum's recommendations. Getting after it in the morning.

Re: Advice on Solving Voltage Drop to Starter

Reply #20 – March 04, 2022, 01:41:27 am

Problem solved. As advised, I removed both POS and NEG single factory common posts which were surprisingly in good shape. I substituted 2 Marinco 3 terminal 600amp buses through bolted to the chassis. Shined up the patinaed copper lugs and coated everything with No-Ox-Id. Just because it was easy, I replaced both the POS and NEG 3/0 cables from the battery bank with 4/0 Marine tinned copper cable to the new buses. Voltage drop now under .5V at all points and it starts readily. I was really shocked at how many cables the factory stacked up on those single common terminals! Thank you all for laying out the solution and advising me on how to proceed. I am very grateful.

Re: Advice on Solving Voltage Drop to Starter

Reply #21 – March 04, 2022, 11:00:35 am

I think it is a common problem. Replacing the common posts and cleaning up all, the connections on mine made a big difference in starter speed and engine starting. Good Job. Keep the No-Ox-Id handy and use it on all of your big connections. It helps keep connections (battery too) clean and keeps stainless studs and nuts from spalling.

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